Science method

UV-Visible Spectroscopy - Science method

UV-Visible Spectroscopy refers to absorption spectroscopy in the ultraviolet-visible spectral region of the light spectrum.
Questions related to UV-Visible Spectroscopy
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This will involve only UV-Visible spectrophotometry but without HPLC
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Dear Abdul-Hammed,
This is actually a fairly simple, and for carotenoids reliable, quantification; although for tomatoe lycopene is really prevalent usually, and this decreases a bit the accuracy.
The general principle is that , as the compounds have different absorbance spectra, they have different absorbtivities for 2 judisciously chosen wavelengths. You build from this 2 equations (for optical densities at the 2 wavelengths) with 2 unknown values. This is general and will apply whenever you want to quantify 2 absorbing compounds, given that they give spectra of comparable intensities (if for example for one of them the OD is one, and for the other 0.01, it will not work well, errors in measurement become too much for reliable quantification of the minor compound) but different shapes (not too close either) in your concentration ranges. For carotenoiids the judisciously chosen wavelengths correspond to absorption peaks at 503 nm(one of the maxiima of lycopene) and 450 nom (for b-carotene). :
(Conc Lyc x Abs Lyc 503 nm) + (Conc Car x Abs Car 503 nm) = OD 503
(Conc Lyc x Abs Lyc 5450 nm) + (Conc Car x Abs Car 450 nm) = OD 450
The absorbtivities you may determine yourself using standards, or, as the standards for carotenoids are often of low purity, use reference values.
The actual references for that are quite old, but there was just recently a quite good article for these procedures in Postharvest Biology and Technology 66 (2012) 16–22.
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I have performed an experiment on detection of mercury using gold nanoparticles. The color of the concentrated gold changes from red to blue. I have taken UV-Vis spectroscopy for each aliquot. I think the UV-Vis spectrum is not showing the good result. I am attaching my spectrum. Please tell me if the result is correct.
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I assume that the two set of spectrum correspond to presence and absence of mercury. I would say that it depends on the concentration of mercury that you are dealing with. If you are working in ppm level may be this is fine.
I remember reading a paper for sensing mercury using goldnanoparticles colorimetrically may be if you get that paper you will get clear.
How to calculate optical bandgap of a multilayer thin film material from absorption or transmission spectra?
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The ZnO films were fabricated on FTO coated glass substrates with known thickness. Please suggest a method to calculate the optical band gap, from its absorption or transmission spectra.
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If your films are of enough good quality (no diffuse scattering), I think you should fit the transmittance and reflectance data using algorithms based on the coherent transfer matrix formalism. This formalism is used by commercial software and takes into account the effect of reflection, transmission of light at each interface, together with its propagation in each medium. Calculations take into account the complex nature of light (amplitude and phase), interference effects, etc, and can be done for multilayer structures. From that, you should extract the complex refractive index of the thin film of known thickness (if made of an homogeneous material). For a multilayer based on two different materials, you should know the layer thicknesses, and if possible the complex refractive index of one of the two materials and then you may obtain that of the second material by fitting. From the obtained complex refractive index you should finally obtain the absorption spectrum of the unknown material and information about its "optical bandgap".
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I mean how we can realize if this ligand has coordinated via S atom or N atom?
Difference in charge transfer ability?
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Actually the best way to determine if the NCS is N- or S-bound is using IR spectroscopy. The are two bands to be aware of the CN stretch and the C-S stretch. For a terminal N bound NCS these should be at 2050-2090 cm-1 for CN and 800-825 cm-1 for the C-S stretch. If the NCS is S bound it should be at 2100-2120 cm-1 for CN and 710-730 cm-1 for the C-S stretch. For bridging NCS the CN stretch is a real give away being usually greater than 2140 cm-1, the C-S stretch is in the middle about 780-790 cm-1. There's an excellent paper on this in the Journal of Chemical Education (doi: 10.1021/ed100284z).
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I have studied an article which relates the number of graphene oxide layers (suspended in water) with its UV-vis spectra (the article's pdf file is attached). but I need to determine the number of Reduced Graphene Oxide layers in a water suspension (graphene oxide tends to settel after reduction and it worsens the problem)! Can anyone suggest a suitable method? Thank you in advance!
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Dear Sina,
if reduction leads to agglomeration/settling UV/VIS spectroscopy will not be able to determine precisely quantitatively the content of reduced graphene oxide. Qualitatively you may determine the content of graphene oxide in suspension.
Elemental analysis of separated solids (C and O) would be a more appropriate method.
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How to decide which type of baseline correction (straight line, polynomial or manual etc.) is required for peak fitting? I have number of spectra of unknown samples for analysis but the problem is if I select some baseline then it may remove some peaks which may be characteristics of the compound .
I am using Peakfit and Origin for analysis.
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Yup i have access to spectrometer , its in my lab only. I already did reference correction and then recorded spectra of my all sample and i know that instrument has already subtracted baseline but still have a doubt whether i need to do it further to make spectra more symmetrical .
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With gas chromatography the concentrations of some impurities are already determined. In addition how can the UV absorbance at 240 nm during UV-Vis Spectroscopy or other methods be used to determine the concentrations of the remaining unidentified components in pharmaceutical grade ethanol?
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Use a calibration curve or set a máximum absorbance limit like the Pharmacopoeia does.
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With the Powersoil extraction kit we get high DNA concentration readings and high contaminant ratios by UV-Vis spectrophotometry. However we can not visualize the DNA in agarose gels (1% or 0.7%).
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Hello, please see attachment, here the well known universal DNA extraction method. You can use it for many approaches. If necessary I can send procedures for extraction.
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band gap calculation of nanomaterials by UV -Vis, Photoluminiscence and Cyclicvoltammetry
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You need to identify if the two transitions are obeys the direct or indirect absorption, that was not obeyed, then you may have one of the transitions be due to defects and the other due to the bund transition
Prof. M S Omar
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I have a assay where absorbance has to be measured and in which the A% value is given and I want to find out the % of the material present.
The method is according to the pharmacopeia .
please guide.
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Use this: A= A(1%,1cm) * b * c
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I have prepared polymer that forms gel in presence of metal ion and also shows a significant change in color. Initially I tried to calculate the binding constant of the metal with the polymer using uv-vis and expected to get a trivial job's plot. However the polymer absorption is going on increasing on addition of metal ion but never reached saturation point. I would like to know whether we can calculate binding constant from it or not. Also I would like to know if any other methods can be used or not.
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As you have observed the sharp changes in color, I assume that the gel reacted efficiently with the metal ions. However, normally metal ions interaction with the polymer is not that effective as, for instance, in the case of interpolyelectrolyte reaction with proteins, DNA, dendrimers, or other polymers. Thus, the metal absorption in the case you have studied should be a combination of real binding to some active sites of the polymer, and the passive diffusion into the gel phase (it is known that even if the polymer does not specifically interact with the metal ion, you will always find some inside the gel after equilibration). The latter term can be described by the equilibrium distribution (of the metal between the two phases) constant, taking into account the volumes of the phases (gel and solution) and the metal concentrations inside the phases. Thus, as you take more and more metal, it will penetrate inside the gel even in all the interaction sites are already occupied - just because there is some water in the gel, and this is enthropically favorable.
Thus, the real constant of the metal binding to polymer can be estimated if you extend the equation to account for both constants: binding (and the active sites concentration within the sample) and distribution (do not forget about the volume of the gel that is likely shrinking upon the interaction). The fitting of the experimental data to the equation will give you both constants; you can check the distribution constant - it should be close to unity or slightly less)
Alternatively, you could probably run the desorption experiment for the samples loaded with a varied amount of metal, however, I do not think it will add much to your knowledge. Just if you have some spare time, ha-ha.
Apart from the above-mentioned reason, the cooperative increase in the absorbed metal amount could be due to formation of some special metal clusters within the gel. This could be if the metal bound to the polymer could act as a nucleus for the efficient cluster formation because of some electronic or chemical change. However, I would start with the more simple and common consideration of the passive diffusion first; anyway, the special cluster formation cannot be seriously discussed without additional info of the actual chemistries you are using.
Ah, and there is one more possibility, If upon interaction of the gel with metal ions some dewatering does occur, this means that after very first portion of metal absorption the concentration of polymer chains in the gel would increase, this could also bring some effect of the binding constant increase as the gel is loaded with more of metal. However, if this was the only reason, you would anyway reach saturation at some point.
Is it possible that UV-Vis spectra show a sharp Absorption line only at one point?
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Nanocomposites of Co2O3
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Thanks for clarification.. It was due to system error and it was not that much specific in only 1nm but very small sharp band in few nm..
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I want to know the concentration of my gold nanorods but I only have its UV-Vis spectrum and do not have any of its TEM image. The AuNRs were synthesized using the seed-mediated method using CTAB.
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It's possible in principle. If you can measure the extinction spectrum, then, assuming your nanorods are fairly uniform, calculate the extinction cross section of a single rod (either an analytical solution exists from mie theory, or probably has been computed using FDTD or other numerical methods), then your extinction spectrum should be the extinction cross section TIMES the number of rods in the solution.
In reality, this is not very accurate. First, because you are likely to have a distribution of nanorod sizes and shapes, not of a single population. Secondly, the computation is highly sensitive to the dielectric function of the material, and from similar inquires onto gold nanospheres, there's an inherent measured error between the theoretical and experimental extinction spectra. For nanospheres, people have done this calibration emperically, so that just by measuring the absorbance, one is able to get the concentration.
PS, if you know the concentration of the reactants used to make the particles, and you assume the reaction went to completion, and you can measure the particle size (TEM/AFM/SEM), then you can estimate the concentration of the rods. Again, this suffers from approximations of particle size distributions like the aforementioned method.
In short, there's no sure-fire way that I'm aware of to do this, unfortunately.
In finding band gap, which method is accurate: tauc plot or shapiros method?
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Band gap calculation
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Please check on these links; www.msri.org/people/staff/levy/.../kumar-bandgap.p..., dspace.mit.edu/bitstream/handle/.../36962405.pdf?... and tel.archives-ouvertes.fr/docs/00/79/98/15/.../these_Kamil_FEDUS.pdf‎ You will definitely get some links Regards,
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Actually I didn't need the exact quantity. Even an approximate is fine. Is there any free database or site? Or I have to do experiment?
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you can linearly estimate if you know the RI of the components and their relative proportion in the solution
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Please suggest a simple method of determination of chloride in berberine tannate. The method given in JP (Japanese Pharmacopoeia) is very complicated and is very confusing.
Please suggest any better and simple methods of quantification. UV spectrometric method would be preferable.
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Hello there,
Use a Fluoride ion selective electrode for the analysis. alternatively use ion chromatography which is less tedious.
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Interested in user experience to make a good choice. The critical parameters:
- EMCCD, the chip is ~512x512 or more pixels;
- High QE (>90%) @650nm;
- Vertical binning: from 1x2 to 1x(full vertical), the more options, the better;
- 16bit digital resolution.
Frame rate, interface options are not critical.
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We use Andor iXon X3 in vertical binning mode 512pix x 20zones with fastest acquisition of 1.6ms, the Andor iXon Ultra should be faster (up to 1ms in the same setup). For details see http://www.andor.com/pdfs/literature/Andor_iXon3_EMCCD_Brochure.pdf (pages 34-35)
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UV spectroscopy.
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You can add some hdrogel to absorb heavy metals. Then determine by standard methos.
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I am investigating the excited state of a pyridine N-oxide by laser flash photolysis (308 nm). I am looking for different probes to react with the excited state that can react by either one or two electron and preferably yield products which are detectable by absorbance measurements. The molecule must be soluble in either water or acetonitrile and should not absorb appreciably at 308 nm (at sub-mM concentrations). I have had success with ABTS in water (one electron oxidation of ABTS2- by the excited state followed by a back reaction yielding ABTS2- and ground state N-oxide), but the chemistry is much more complicated in acetonitrile. I have also attempted to use TMPD (in water) and tetramethylbenzidine (TMB) (in acetonitrile with varying concentrations of water). Both of the latter compounds have their own photochemistry and the varying degrees of protonation and solubility are problematic. Does anyone have any suggestions on suitable probes?
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Please use this link and get the answer;
The electronic states of pyridine-N-oxide studied by VUV photo absorption and ab initio configuration interaction computations
Michael H. Palmer1, Søren Vrønning Hoffmann2, Nykola C. Jones2, Elliott R. Smith3, and Dennis L. Lichtenberger3
1School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, Scotland, United Kingdom
2ISA, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
3Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721, USA
Regards
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We are doing a UV-Vis analysis on an aromatic polyimide sample using a UV-VIS Varians Model. We have got the result as shows in the attached file. The micrograph shows noise below a wavelength of 300 nm. We do not know whether the noise is coming from the equipment or samples.
Method
The probe has been dipped into the sample solution. Initially the solvent has been run as a background, followed by the series of sample solution.
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The spectrum you show is the result of dividing the spectrum of light transmitted through the sample with a reference spectrum. The noise in your spectrum is very typical of a reference spectrum that is nearly 0 at UV wavelengths--essentially you are dividing by noise at short end of the spectrum, which is why you get those wild gyrations. There could be four reasons for this problem:
1. The light source is very weak in the UV. Check that the UV lamp (usually a deuterium lamp) is on and not broken. The lamp could also be close to the end of its life, which would make it emit much less light than when it was new.
2. The detector you are using is not sufficiently sensitive in the UV. This is more likely to be a problem at long wavelengths, but I mention it here anyway to be complete. Some spectrophotometers have multiple detectors, and you need to make sure you have selected the right one in the software.
3. The spectrophotometer is not selecting the right filter when scanning through UV wavelengths. The internal filters are there to suppress higher order diffractions from the monochromator grating, and need to change as the wavelength changes. In most cases this should be done automatically, so if this is the problem your instrument may need to be serviced.
3. The reference sample has very low transmission in the UV. In my experience, this is the most likely reason, at least if you are supplying a blank sample in the reference beam. Make sure your cuvette (or substrate if you are looking at a film or a solid) and any solvent you are using actually transmit light below 300 nm.
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My UV absorption shorter cut off wavelength is 301 nm? How can I PL study for my material?
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If your material absorbs shorter than 301 nm you must use the excitation wavelengths shorter 301 nm. It may be observed the photoluminescence spectra caused by different defects. They can be situated in more longwavelength spectral region. I suggest you use excitation source with the shortest wavelength which is available at your disposal. It is possible you may observe photoluminescence caused by defects.
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The dielectric function of Ag-Au Au-Cu alloys of various compositions.
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What about this paper?
Moskovits et al, J. Chem. Phys. 116, 10435 (2002)
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I don't have enough information about it and if someone knows please guide me through it.
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Difficult! Absorption around 200 nm. Use HPLC!
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Does anyone know a free online UV-Visible spectra database where someone can compare and verify their experimental spectra with? I am dealing with organic compounds (e.g. phenolics).
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Sorry, my fault.
Here some alternatives.
NIST Chemistry WebBook
PubChem Substance Database
Colby Organic Database
Sigma-Aldrich
(To View Spectra:Find a substance using either the Data Specific Search or the Structure Search. Click on the substance number, then the Safety & Documentation tab; PDF spectra are linked on the left column, under the Certificate of Origin search.)
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I need to find a UV maxima library for phenolic compounds in arabidopsis and or poplar.
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How to determine an exact excitation wavelength in PL measurement based on the UV-Visible absorption spectrum studies? How to interpret defects based on PL peaks in single crystals?
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You'll need a long-pass filter, which filters out the whole wavelength range shorter than the known prominent peaks of PL emission. You install this filter between the sample and the detector. If your sample does not emit, you'll have zero signal in the stopband of the filter. If there is any luminescence, you'll see peaks exactly corresponding to your excitation bands. I did it on translucent thin films in the transmission mode (http://www.sciencedirect.com/science/article/pii/S0921510712003765). For the reflection mode arrangment, it would be not that straightforward but still feasible. The interpretation is another question. All I can say is that I don't expect much difference for the polycrystalline and monocrystalline samples.
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Does anyone know the UV-vis absorption spectrum of C70 in CS2 and the UV-vis of CS2?
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And here is a link to a paper reporting the UV-Vis spectrum of C70 in different solvents: http://www.nipne.ro/rjp/2009_54_5-6/0529_0539.pdf
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In a UV-vis apectrophotometer, what does it mean if the absorption spectrum is coming in the negative region of the y-axis (absorbance) even after taking a baseline with reference?
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Dear all, 
I would also thank you very much for all your advice and comments, they was really helpful for me  as well.
Am also got negative result in one of my experiments, its happened when I diluted the suspension 20 times before the test with uv-vis. but with the diluted factor was just  ten times the absorption  was fine (between 0-1).
Please let me know if you can explain more about this phenomena.
Regards 
Salam 
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I did my research using UV Visible spectroscopy and was wondering if there is a better method of analyzing nitrate, nitrite and phosphate in fluids like water or alcohol
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Nitrate may also be determined by several methods including ion chromatography, liquid membrane electrodes, and colorimetrically using a UV - VIS spectrophotometer.
Nitrite seldom appears in concentrations greater than 1 mg/L, even in waste-treatment-plant effluents. Its concentration in unpolluted surface and ground waters is normally below 0.1 mg/L. Nitrite is also commonly measured using ion chromatography, liquid membrane electrodes, or colorimetrically.
As with organic nitrogen, in order to determine organic phosphorus the organic compounds must first be oxidized. This may be accomplished by any of three methods involving perchloric acid, nitric-sulfuric acid, or persulfate.
Many researchers use both UV-Vis spectrophotometry and electrode techniques for the determination of nitrate, nitrite and phosphate in water/alcohol samples.
Other methods are convenient for laboratory measurement, but on site, suspended solids, turbidity, contamination and interference mean that results may not be reliable. Moreover, they need reagents which have many disadvantages: high operating costs, poor stability and water pollution.
UV Visible Spectroscopy is the only method which gives high stability and high reliability for on-line measurements, the effective low maintenance and low operating costs of our on-line analyzers.
The advantage of the electrode method is that it is fast and can be carried out in the field.
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The energy levels are labelled as 1A, 1B, 2A and 2B from ground energy level to higher excited states for F+ center. Could someone suggest some basic papers on its nomenclature and a necessary theory?
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Dear FM,
thank you so much for illuminating this topic with your relevant and much awaited reply,
kindest regards
N S Rawat
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We have synthesized a push-pull 4,4'-bipyridine containing azobenzene dye and we have prepared its stoppered inclusion complexes (rotaxanes) with α and β cyclodextrin. (The inclusion complexes formation has been varified using various spectroscopic techniques).
Surprisingly, in the UV/Vis spectra of the rotaxanes, the molar extinction coefficient of the azo π-π* band increases (it gets even 50000 1/(M.cm) that is almost double as compared to the cyclodextrin-free dye. I cannot find any information which could explain this behavior, therefore I would be glad to read your opinion.
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May be you have some kind of pi-pi interaction or aggregation formation that can occur inside the CD.
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.
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The nano particle generation by laser in aqueous media is mainly due to. Laser ablation. Therefore, the laser properties may alter the nano particle size distribution. Those are laser wavelength, laser pulse energy, pulse repetition rate, laser power density and the media where laser ablation and particle condensation take place.
What can I know from UV-Vis in BaTiO3 measurement?
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Very few reports on this kind of characterization and non-uniformity in their results. What kind of information can I obtain from this measurement? BaTiO3 is a dielectric.
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In the nanometer range there should be a dependence of the maximum on size of the particles and accordingly of the ratio of the extinction on two wavelength.
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In our fluorescence spectrophotometer, I excited pure ethanol at 283 nm and I found a peak at 314 nm.
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possibly Raman scattering if it's a sharp peak unlike broad emission bands. Change the excitation wavelength to check if the so-called Raman peak position changes nearly proportionately. Usually the shift between excitation wavelength and Raman peak position lies within a fixed range for every solvent. It's usually weak and does not matter if the fluorophore you are going to measure in the solvent is highly fluorescing. You can try making the instrument slits smaller or you can also do an easy background subtraction.
Good luck !
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I'm looking for the graphene dispersion concentration.
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then you have to prepare solutions of know concentrations and plot their absorbance values vs. conc. to follow the straight line equation y=mx where y is the absorbance and x the corresponding concentrations. Keep in mind that if the concentrations obey the Lambert-Beer law, the plot will be a straight line. From the plot obtain the slope m. Then simply replace the absorbance (y) of the unknown conc. into the equation where you know the m. You get your concentration. This can be done very easily using excel, origin or igor.
At too high conc. there will be deviation from linearity i.e. the law is inapplicable. There are several reasons for this which you can look up in your own interest in some good book or over the net.
Hope this helps. Good luck.
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The absorption spectrum of my compound has two peaks, 320nm and 327nm (in DMF. ~1e-6 M, abs = 3) and the region between 260 -200nm has scrambled (noisy) pattern. While measuring the absorption spectrum, anyone of the 320nm or 327nm peak was always scrambled. If i increase the concentration then both peaks get scrambled. In methanol, the spectrum was neat (no scramblings) contain peaks at 216nm, 247nm, 315nm, 327nm(this peak was more intense and little bit scrambled) the compound is pure (by NMR). the compound is soluble in DMF but sparingly soluble in methanol. In methanol, when regarded for another batch of the same compound, the spectrum has no 327nm peak. i want to know why these scrambling appear and what could be the fact underlying behind the 320 and the 327nm peak. my compound is symmetric. can anyone explain these observations?
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I agree with the answers of Jiri, Geoffrey,Rupashree, Subramani . But please note:
- NMR purity is not good enough.
At first , you need an elemental analysis of your drug . The "found" values must be + / - 0,1-0,2 % related to the calculated values. Before you give your drug for elemental analysis, you must dry it in vacuum (presence of water or solvent acquired during the synthesis) until the elemental values remain constant.
When you dissolve your drug in a pure spectroscopical solvent for UV-Vis, your solvent must be dry and fresh distillated.
UV/Vis solvents have a CUT OFF value (see above)
UV cut-off
(nm,
T1cm <10%)
1,2-dichlorobenzene 295
1,4-dioxane 240
2,2,2-trifluoroethanol 190
acetone 329
acetonitrile 190
benzene 278
butan-1-ol 229
cyclohexane 195
cyclohexanone 340
dichloromethane 232
dimethyl sulphoxide 262
dimethylacetamide 267
dimethylformamide 267
ethanol 205
formamide 210
methanol 205
methyl isobutyl ketone 335
n-butyl acetate 255
propan-1-ol 205
propan-2-ol 205
propionitrile 220
pyridine 310
tetrahydrofuran 215
toluene 285
water 180
The NMR and UV-Vis solution of your drug must be FILTERED (VERY IMPORTANT /Presence of a stable dispersion or suspension before filtration) prior to measurement and your quartz cell must be closed.
Are you using single beam, dual beam or diode arrays spectrophotometer (Very important too)?
Another hints in due course after answer. Good luck
JRG
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I need to take a spectrum of ceftazidime which is a cephalosporin antibiotic. I want to determine the wavelength having peak absorption
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Prepare a solution of concentration 10 ug / ml ... and sweep the UV spectral region between 200-350 nm
Does anyone work on energy levels and dynamics of Pb doped CaF2 under UV and VUV excitation?
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I would to know what people found already about that.
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Divalent Pb does not introduce defects into CaF2 lattice, so, to my opinion, UV and VUV will interact with those intrinsic to CaF2 itself. Concerning Pb2+ levels, I have no data on its position in fluorides. it depends on the crystal field. In PbSrB4O7, fundamental absorption edge is found at 237 nm (corresponding bandgap 5.75 eV) with the distinct sideband protruding up to 300 nm. Fundamental absorption must be formed mainly by the transitions originating from 1S0 → 3P1 transition of free Pb2+ ion that is split into two components at least in nine-fold asymmetric crystal field within PBO crystal. Additional band observed at 350 nm is found in our sample, too; it can be assigned to interband transition originating from weaker transition 1S0 → 3P0 of a free Pb2+ ion. For Eu2+, crystal field in SBO is weaker than in CaF2 but I have no such data for Pb2+ ion.
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My compound shows the maximum absorbance at around 260 nm. But the maximum intensity in excitation spectrum appears at 300 nm. The excitation spectrum has been corrected. I wonder which maximum value should be involved in stokes shift calculation.
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When absorption and excitation spectra do not match, there is a severe problem. There can be a number of reasons. First: sample impurity. That has to be checked first. Absorption spectroscopy alone often is not sensive enough, depending on relative fluorescence quantum yields of sample and impurity and/or differences in absorbance at the excitation wavelength. Keep in mind that spectral calibration is not a simple issue. Also photoproducts can lead to difficulties. Check as a function of irradiation time.
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I want to find the band gap of Al2O3. Is it possible with UV-vis study?
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Yes, it's possible using steady state absorption spectrum. Do you have the absorption spectrum of alumina ? Then just using the cut-off wavelength from the spectrum in the formula E=hc/lambda calculate the band gap energy. Hope this answer helps you. By cut-off wavelength I mean where the absorbance value is minimum before showing a distinct rise. You can infer the same cut-off wavelength information from the reflectance spectrum also.
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I have a solution of TBS (pH=7.4) and 30nm gold nanoparticles coated with NHS polymer. I want to read the absorbance of such molecules but I cannot seem to fully resuspend the particles, there is always a precipitate. The absorbance readings are very low, and I believe it is due to the fact that the particles are not in solution, they precipitate. Is there a protocol for best resuspending gold np's and measuring its absorbance?
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And maybe is not a good idea to have the AuNPs in TBS...
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I have data in terms of absorbance and % transmittance vs. wavelength.
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See the attached paper for detailed discussion (in particular, Eqs.(5) and (6)).
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I dispersed 0.2mg/milt SWNT 95% purity (1-2nm OD) in 2% SDS and sonicated for 2h using tip type sonicator with 2W power and 70% cycle. I use a sample of it for Uv-Vis spectroscopy. The result is in attachment. While in all reports on Uv-Vis of SWNT there is two or rather three peaks related to metal and semiconductor transitions, I only got one peak. I would wonder what the problem is OR how I can interpret this one peak?
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Well, I don't have time to read the paper completely but isn't it correct that in the second one an ultrasonic processor of 750 W at 26% of full power was used? This is more or less 200 W, which is two orders of magnitude higher than you try. If this is really the case, firstly, you can easily increase the power at least tenfold, and second, this is no wonder that your CNTs don't get dispersed.
Strong agglomeration may happen to be the reason why you cannot find transitions described in those papers like "Diameter grouping in bulk samples of single-walled carbon nanotubes from optical absorption spectroscopy" or "Optical Properties of Single-Wall Carbon Nanotubes"
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If samples (lignosulfonates or precipitated lignins) contain high content of ash, does the ash have a negative effect on the determination of UV spectroscopy? Are more purified samples are better?
On the other hand, the ash that is in addition to finding reflects the purity and amount of inorganic chemistry (Ca, Na, ..) which is incorporated in the compound (example: lignosulfonates C20H24CaO10S2).
Purification of samples results in the changes in the content of OH groups.
Example of Samples and content of ash:
Vanisperse 34.2 %
Boresperse N 23.3%
Orzan 10.8%
Precipiataed Kraft lignin 3.9%
Precipitated lignin II. 0.4%
UV spectroscopy
After being dried overnight at 80°C, precisely weighted amount (about 5 mg) of the lignin was dissolved in 5 mL of dioxane and 5 mL of 0.2 M NaOH. Some of the solutions were not quite clear and these were filtered using a 0.45 m PVDF membrane filter. From each lignin solution, 2 mL was further diluted to 25 mL using either a pH = 6 buffer solution (citrate — NaOH, Merck), and 0.2 M NaOH solution.19 This gave each solution a final concentration of lignin of about 0.08 g/L. UV-Vis spectra were recorded on a CECIL spectrophotometer in the absorption region 200 - 450 nm, scan speed 5 nm/s and resolution 1 nm. Lignin solution with the pH = 6 was used as a reference and the alkaline solutions measured against it. From the difference spectra, the absorbance values at 300 and 350 nm, measured against the solution containing 0.2 M NaOH were recorded. According to an original work of Gartner et al.six structural types of phenolic structures exist (Fig. 1). Maxima at 300 nm and 350-360 nm are assigned to unconjugated phenolic structures (I and III) and that at 350-370 nm to conjugated structures (II and IV). According to Zakis et al. the maximum at 360 nm is attributed only to IIa and IVa types of phenolic structures in lignin.
a) Non-conjugated phenolic structures (I + III)
OH(I + III) = {(0.250 x A300 nm(NaOH) + 0.0595 xA350 nm(NaOH)} x1/(cxd) (eq. 1)
b) Conjugated phenolic structures (II + IV)
OH(II + IV) = {0.0476 xA350 nm(NaOH)} x 1/(cxd) (eq. 2)
c) Total amount of phenolic hydroxyl groups
OH(I + II + III + IV) = {0.250 x A300 nm(NaOH) + 0.107 x A350 nm (NaOH)} x 1/(cxd) (eq. 3)
where Aλ – absorbance at a given wavelength divided by the corresponding molar absorptivity, c – mass concentration in g/L; d – pathlength through the sample in cm.
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Hi Michal,
Of course the more purified samples are quite better. This due to the interferences between absorption peaks of UV absorbents species. In other words, The appeared peak in the UV spectrum may be is a sum of different absorbents species including the impurities. On the other side. If there is no interference within the peak, the impurities will affect the absorbance through molecular interactions. Furthermore, the molecular interactions also affecting the Uv-visible spectrum for single pure molecules which concentration depended (causing deviation from Lambert-Beer model).
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My samples were characterized by PL and UV-vis spectroscopy. Using these two methods, the values of band gap had small differences. I think that PL shows the emission incorporated with defects such as Cu vacancy, Cu on Zn, Zn on Cu and so on. Is this correct?
How do I mark these defect levels in PL results?
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This article will be helpful for you
Absorption spectra gives you the best information of band gap. In your case try to take absorption spectra in UV-Vis-NIR region.
From temperature dependent PL you will be able to identify the the defects in the material by calculating their activation energies.
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This software is very useful for visualisation and processing of UV-Vis, IR, FT-IR, NIR, Raman, fluorescence spectra and is freeware for researchers.
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Dear Dr. Sridhar, Dear Raja
thank you very much for your fast answer. Have you encountered any problems with Spekwin in the new version?
Have you any suggestions in order to make the software better. Can I ask with what a kind of spectra you worked?
Thank you in advance for your answer.
Best Regards
Jean-Rene
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Is there any solvent for dissolving borate glass for UV (UV-vis spectroscopy) and PL (photoluminescence study) measurements?
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why should one dissolve glass for photoluminescence measurements? What do you expect from such a solution?
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I doped Fe2O3 with direct band gap semiconductor material to improve its photo current, but there is NO improvement in its photo-current after doping.
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With doping you'll get an increase in conductivity of a semiconductor. For photoelectrochemical applications 1-5 or even up to 10 at.% doping is a 'sweet spot'- or rather a place to start. This all depends on the materials you're using and what dopant, and even synthesis method. How does 2 or 7% loading perform in comparison?
Doping can create low lying trap sites which can help to prolong electron lifetimes, which can lead to increased photocurrent given specific conditions. If the trap sites become too dense from doping, however, they can act as recombination centers thereby reducing photocurret.
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I have grown organic single crystals which are a deeper yellow (slight orange) color? UV-Visible shorter cut off shows 501 nm. How can I identify if there are any chromic effects in crystal?
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Hello Mr. V.J,
I hardly understand chemistry you are talking but from thermal point of view I can comment on 'Chromic effect',
let me understand your question, do you mean a surface treated with chromic acid?
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Uv-spectroscopy
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Stock solution of heavy metals like lead, arsenic, mercury and copper.
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Specially in vegetable oil..
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Other than UV you can do a quantitative analysis for Cl. First you need to do a sodium extraction then precipitate Cl using Ag or Hg or Pb ion solution or you can do a redox titration and measure the protential.
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If anyone has both the uv vis spectra and colorimetric data (CIE 1931 values) for onme or a couple of coloured samples and could share the data please could you post / send to me?
I need uv/vis at 5nm increment minimum.
I wish to test my software to see if values agree.
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Happy to do that except that it will be 380-5-780nm (ie no UV as not needed for colorimetry) and would you like the calculations for CIE 2 degree and/or 10 degree observer and Standard Illuminants A and/or D65? (I also have B, C and easily available.
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Ag NPs colloidal solution have a characteristic peak at about 390-420 nm using UV-Vis spectrophotometer. The intensity of the peak is proportional to the concentration of the Ag NPs of the measured solution. The attached file is one of my Ag NPs samples measured using a UV-Vis spectrophotometer. The original sample is diluted "x" times in order to be measured correctly. The values of the absorbance on the Y-axis obtained from the instrument is then multiplied by "x" and re-drawn by the Excel program.
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While it has been a little later than I expected, I recently published an article on this issue in the RSC Analyst, which will be free for the next few weeks. The Supplementary Information (always free I believe) contains a comprehensive table of extinction coefficients of citrate-coated silver nanoparticles, from 8nm to 100nm in size (2nm steps). I hope this will be useful.
I decided to add an extra part to this original post. It should be noted (previously, maybe incorrectly, I assumed this is known) that for the small silver nanoparticles with Lmax between 390 - 410 nm or so, addition of a monolayer (e.g. a SAM) will change this Lmax value, most likely with up to a 15-20 nm red-shift. Hence the paper concerns citrate-coated silver nanoparticles. We wanted to add this info into the above Analyst paper, but the reviewers suggested to not do so. Plan to publish something else on this in the near future (fingers crossed :-)  )
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I ran a ton of samples and the basic idea is comparing UV-Vis technique with AA/AE technique and we were asked to compare molar absorptivity to literature values when using UV-Vis, but now I am processing a ton of AA/AE data and molar absorptivity information is like a needle in a haystack. Is it that molar absorptivity, or extinction coefficients are simply not a useful piece of data? (With respect to my current experiment, I have seen a few applications aside from AA/AE where it is in fact useful) Any information from you scientists out there would be useful, if not only to quench my curiosity! Thanks!
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That makes perfect sense and definitely satisfies my curiosity. Reproducibility of molar absorption measurement, when the variables which affect it are inconsistent, highly dynamic, or difficult to measure may lack significance.
Thank you for the feedback Karl!
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What are the effects of conjugation on UV-VIS peaks?
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The nature of this band is mainly depending on the chemical structure of your molecule, but for aromatic moleculeslike naphthalene or anthrathene these bands are for vibronic excitations
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Interpretation of UV-Vis spectra
(take a look at the attached figure)
For each type of isolated precipitate lignin from black liquor (hemp and flax; modified alkaline anthraquinone cooking) precipitate of sulphuric acid (5, 25,50 and 72 % w/w), a stock solution was prepared by dissolving lignin powder in NaOH (0.1 M). UV-VIS absorption spectra were registered using a solution of lignin on a CECIL spectrophotometer, absorption region 200 -450 nm, scan speed 5 nm/s and resolution 1 nm. Measured values of absorbance were normalized at 222nm (maxim bands). The free and etherified hydroxyl groups contributing to the characteristic absorption maximum of lignin near 280 nm. The lignin fractions showed a characteristic absorption band at 284 nm, which could be assigned to the unconjugated phenolic groups of lignin.
Adsorption maxima of unconjugated quaiacyl and 3,4-dimethoxy-phenyl model compounds fall within the narrow wavelength range from 277 to 282 nm. In alkaline solution, ionization of the hydroxyl groups shifts the absorption bands of compounds with free phenolic towards longer wavelength.
The pronounced shoulders at 242, 257, 280 and 312 nm on the lignin ionization curves in alkaline solution indicate the presence of biphenyl derivatives. These structures may be aromatic, containing non-etherified hydroxyl groups, conjugated carbonyl groups and aromatic carboxyl groups in lignin.
I also need help in the interpretation of the absorption band at 222 nm.
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Maybe you should try to do some computational modeling on lignin. It's big system, but maybe some semi-empirical methods will work on it.
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I want to measure ROS generation in cells following drug incubation, using a dye (amino phenyl fluorescein - APF) that becomes fluorescent in the presence of ROS. The kit protocol is meant for imaging using confocal, but I would like to modify it to do a quantitative spectroscopic measurement. What I plan to do is: incubate the drug with cells growing in a culture dish, harvest the cells, spin down to form a pellet, re-suspend the pellet in 2 ml HBSS, add APF, leave it for 15-30 mins and measure the fluorescence using appropriate Ex/Em filters. My question is: should I lyse the cells after the addition of APF, just before doing the fluorescence measurement?
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usually there's no need to lyse cells. If your cells are adherent cells you could perform the whole test in a 96well plate (with black walls) and read the fluorescence by a microplate reader. I use the DCFDA dye for ROS and it works quite well.
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ROS Measurement
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You can monitor singlet oxygen production by chemical method with DPBF (1,3-Diphenylisobenzofuran) in organic solutions and with ADMA (anthracene-9,10-diyl-bis-methylmalonate) in aqueous solution. 
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We have an Agilent 8453 diode array UV-Vis spectrophotometer. I am looking for a procedure (script, soft, etc.) enabling us to collect successive, like from a kinetic experiment, and to save the whole set of spectra as a matrix or as a vector and be able to export the latter two in txt or csv formats.
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I used the same UV-Vis diode array. Unfortunately I had to collect data every 15 seconds. I was able to save thelist and export it. For processing I had to select every data set, open the actual data table highlight all and copy. Then I was able to import it in any good plotting software such as OriginLab, SigmaPlot, etc.
It is very time consuming so I share your pain!
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I have got many references suggesting to use Atomic adsorption spectrophotometer, and one for detection of reduction in lead conc. by uv-vis spectrophotometer through calibration curve.
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Thank you Mr. Titus but will you please elaborate your answer..?
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What does a dip in the absorption spectrum indicate?
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Show data! It is possible to attach a spectrum graph or an excel file or anything else to any question or answer. Yor question is just too general to generate useful answers...
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The nanoparticles that I have prepared are in the form of a red powder which have precipitated in the solution. The lamda max is around 568nm. Does the powder consist of copper or cuprous oxide nanoparticles?
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Hi Akhini, generally freshly prepared copper oxide particles do not show any peak in the visible regime in UV-Vis spectra and your 568 nm peak indicates copper particles (generally copper particles show peaks within 560 - 600nm). Here is a reference you can look up: Materials Letters, Volume 63, Issues 3–4, 15 February 2009, Pages 441–443. However, for confirmation, as Matteo and Anjali suggested, you should get XRD pattern. Hope this helps,
Palash
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The UV-Vis was taken an hour after the antibody conjugated with gold was reacted with cells.
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It's likely you are getting additional proteins/molecules binding to the gold particles. Either these are specific proteins binding to your antibody, or non-specific binding is occuring. It's actually quite difficult to prevent non-specific absoprtion onto gold particles without really taking care to coat them with a specific molecule. Even with antibodies on your gold, you're likely seeing non-specific binding.
Changes in index of refraction can also affect the absorption spectra, so the surrounding media of the cell is likely influencing your results to some extent.
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I want to analyse the casein fractions by RP-HPLC UV/VIS detection in milk. Then I want to coagulate that milk by rennet and determine the para-Casein by RP-HPLC. Is it possible? I know that I can analyze the CMP A&B by the same method, but I was wondering if I could detect the para-Casein by RP-HPLC without the use of MS?
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Our spectrophotometer is UV-1800 from shimadzu
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The detection limit depends on the precision of the absorbance measurement. the less the noise, the less the quantifiable concentration. However, my example was a special case. There are not much gaseous substances measurable by UV/VIS spectroscopy. Normally, IR absorbance is used for gas analysis, measured by FTIR spectrometers. For measurement of gases in low concentrations, "multi-pass" configurations are used to increase the measurement pathlength and therefore the absorbance intensity.
Perhaps you should clarify the goal of your question... There are many techniques used in gas analysis like GC GCMS, FTIR, Raman and some more... Again, it depends if want to identify the composition of a gas mixture, or the quantitative amounts of gases, or detect traces of gases. It makes a big difference if want to measure from far away (atmospheric gases) or can draw a sample... and so on...
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I am trying to make hydroquinone from benzoquinone enzymatically.
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how to differentiate between IP3 and IP6 on UV-vis detector of HPLC?
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IP- inositol phosphate
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best way is by their retention times ... being one much more polar than the other one it shoud not be much difficult to undetstand which is which. the very low UV absorbance will be given mostly by phosphate groups and will be in the same range for both compounds,one having an molar extintion coefficient nearly double than the other one they will have peaks area corresponding with their relative amount ... if you have a reference the job will be straighforward probably you will need some secondary detection system to enhance phosphate UV/vis detection ... i am not an expert in this specific issue
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I am in search of a pressure cell with optical (mostly visible wavelength regime) windows, where I can place a soft polymer thin film and squish it under controlled calibrated pressure for spectroscopy measurements in transmission / reflection. Is such a cell available in the market? If a "home-built" contraption is made, what are the possible ways I can calibrate the pressure?
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Hi Palesh,
You need not locate the pressure sensor within the polymer layer itself. If you have say quartz/polymer/quartz/sensor it would be the same. Since as you mention 100nm is very thin, no sensors I know of come close!
To answer you capability question, a vice can be made to almost any specification. Indeed if you want very high pressure you would either gear the mechanism if it was manual or more appropriately move to pneumatics or then hydrolics (in the case of your pressure) and then you can easily know the force you are applying without a pressure sensor! No need for using ftir in this case.
Problem is I dont know if the quartz windows would be capable, probably but 200kbar is high for something not designed for that application.
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Can anybody suggest molecules (dyes) with interesting solvatochromic properties in ground state?
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Mainly organic aromatic molecules having donor moiety like dialkylamino group in one part and the acceptor moiety at the other extreme will show very intersting solvatochromic propety in both ground state as well as in excited state (If intamolecular hydrogen bond or proton tranfer possiblity will be there then also it will be quite good). However I dont know why u r interested for ground state, generally these types of fluoroscents probes shows more interesting behavior in excited state rather than in groud state.
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Attached my file
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Your peak is large and has a lower wave-length that you are waiting. In your case, The wave-length depends on the conjugation of alkene bonds. So, if your product is not presenting the similar structure, particularly if you have less conjugating bonds in your product than is in your graphene reference, the peak that you observe shifts to a lower wave-length. I don't know which process you used to obtain graphene, but if you employed a thermic treatment of a precursor, I think the conversion is not finished at the end of the process.
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I am in doubt about which method i may use to calculate band gap of thin films, if the Kubelka-Munk method using diffuse reflectance spectra or the Tauc method using absorption spectra.
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Here I repeat my answer regarding the question "How to obtain the energy band structure of the semiconductor".
Do you need to test the band gap experimentally ? In this case you can use both optical and photoelectric measurements. Optical studies include the measurements of the absorption, excitonic photoluminescence and reflection spectra. Excitons present the bound electron-hole pairs. Their excitation energy Eex is slightly less than the energy of the unbound electron and hole, i.e. than the electronic band gap energy Eg. The binding energy of excitons ∆Eex in semiconductor is usually about several tenths meV. The energy of exciton reflection spectrum, which present a dispersion curve, is acossiated with the formation of free exciton and determine the optical band gap of semiconductor. The measurement of photoluminescence spectra allows to observe the recombination of free and/or bound to acceptor(donor) excitons. The binding energy of bound excitons correspond about 10 meV (for exciton bound to acceptor this energy is about 0.1 Ea, where Ea - ionization energy of aceptor). In this case it is also possible to observe quantum-zise effect and its affect on the energy structure.
Usually, the traditional method of estimating of band gap of semiconductor materials is based on the results of absorption spectra measurements. However, in the case of polycrystalline films the light transmission depends not only on its absorption resulting from transitions between energy bands, as well as the light scattering by material and additional absorption resulting from the presence of different types of intrinsic defects. All these factors contribute to transmission of light. A evaluation of bandwidth is based only on the absorption measurements as a result of interband transitions. But it is not in the case of polycrystalline silicon. So, you can get any results that are not relevant to the evaluation of bandgap. Measurement of light transmission of polycrystalline films is valid only for the evaluation of their optical quality.
Effective method for the determination of semiconductor band gap is the measurements of the photodiffusion current spectra (see : J. Phys. : Condens. Matter, V.18, 5323 (2006)). This method allows to determine both the band gap energy and the energy of different defects in semiconductor. In this case, unlike photoconductivity, the measurements are made without an applied electric field. And so there is no bending of the energy bands. Usually we used both optical and photodiffusion current measurements. If you need to test of band gap of unknown semiconductor we must first all to carry out the measurements of absorption spectra. In this case you get approximate value of bandgap. Then, it is necessary to perform the photoluminescence and reflection as well as photodiffusion current measurementd described above.
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I detected my sample solution by UV spectrometer, which is believed to contain some alkaloids, however, maybe because of the low concentration of the target compound or due to the sample solution being contaminated, the spectrum shows the characteristic peak as the pure compound with a broad band instead.
I have tried concentrated solution, but it's not ideal. Does anyone know if there are any techniques to isolate the characteristic UV band? Contamination is definitely affecting my experiments on UV.
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WHEN the UV spectrum widens, means there are MORE contributions due to a defect or contaminant with energies very close to those of YOUR COMPOUND. You can try increasing the resolution of the measurement equipment. Or try DILUTE SOLUTION AND GET the baseline.
WHAT IS the measuring equipment are you using?
UV-VIs spectra - DRS - Reg
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In difused reflectance spectra, I get some noise signal at 380 to 410 nm range for all measurement in my instrument. It may due to lamp change from Visible to uv. How can I avoid or nullify that peak?
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It may be not due to lamp only but due to used detector also. You should find out what type of light source and detector are used in the measurement. If you use not a "home-made" setup then you probably can try to configure spectral ranges of light sources and detectors of the device in its configuration. One more, but less probable, reason - an integrating sphere. Try to find out the material it covered and its reflectance in the range
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I have used KIO3 and toulidine blue, but the results are not correct.
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you may follow either the APHA / AOAC to estimate the arsenic from waste waters.
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We are trying to analyse protein activity of the AOX and bc1 complex using duroquinol as a substrate instead of ubiquinol. Usually with ubiquinol you can measure the formation of ubiquinone at 278nm, however duroquinone/ol has an overlapping peak at 270nm in TRIS-HCl pH7.4. We found that in ethanol there are 2 distinct peaks at 263nm and 289nm corresponding to oxidised and reduced compounds but we can't carry out the protein assays in ethanol. Any help you can offer would be greatly appreciated.
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Maybe measure your time points in ethanol? Just remove a small amount of your reaction and put it into ethanol, then measure the UV? The reaction occurs in buffer, but you're measuring in ethanol. I also assume the reaction will be quenched once you add it into the ethanol.
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How can we know about the surface of nanoparticles and its interaction with Uv-Vis light and near FT-IR?
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As I know none of these methods are strong enough to study the surface of nano-particles. But if I had FT-IR and UV-VIS a the only choices, I used some standard methods on my nano-particles and tried to interpret UV-VIS spectra according to the information obtained from standard methods and then apply it on other unknown surfaces to find some overall idea. It's hard to get the details by these methods though.
When determining Kd using fluorescence or UV/Vis, are there any advantages of one method over another?
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I would like to calculate Kd for a ligand-protein complex. My ligand is not fluorescent. What determines if I should use fluorescence or UV/Vis to calculate Kd? Are there any advantages of one method over another?
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It depends on what changes you observe in either technique. ie I generally get a better result from Trp fluorescence for binding assays then absorbance because the absorbance of my sample barely changes, however if you get robust changes in absorbance then that will work just as well. So to determine which technique to use you really need to try them and see whichever one gives you a signal. The main difficulty with analysing spectroscopic changes in relation to binding is determining the concentrations of free and bound ligand, which requires a bit of mathematical modelling. Hope that helps.
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Phazir Optscan, FQA-NIR etc.
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I got a portable "Portalite" for around 11,000 USD
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I am interested in analyzing molten salt mixtures for which I require its spectral properties such as optical constants or complex refractive index (real and imaginary values, n and k respectively).
The spectral range of interest is the visible spectrum (preferably 300nm to 800nm).
I am interested in exploring the following salt mixtures;
1. Ternary eutectic (25.9 wt% LiNO3, 20.06 wt% NaNO3, 54.1 wt% KNO3)
2. HITEC (53 wt% KNO3, 40 wt% NaNO2, and 7 wt% NaNO3) i.e. nitrate-nitrite ternary salt mixture.
3. Solar salt (60 wt% NaNO3, 40 wt% KNO3)
4. Hitec XL (45 wt% KNO3, 48 wt% Ca(NO3)2, and 7 wt% NaNO3) i.e. calcium nitrate salt.
Could any one please shed light as to where I could obtain such data?
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Hi Sarvesh,
The absorption coefficient at the 400-800nm range of nitrate and chloride salts can be found in this dissertation http://dspace.mit.edu/handle/1721.1/62706
Hope it helps,
Georgios
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my thin film is SnO2 on SiO2
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Sara, we have micro-EDXRF instrumentation able to measure thin layers thickness and also to do mapping of thickness along an area, let say homogeneity at millimeter to cemtimeters scale. This is based on measuring the X-ray emmission energy of an chemical element in the layer (Sn in your case) or the depletion of X-ray energy of one element in the substrate, caused by the overlying layer. If you can send some sample I can try to do measurements in my lab.
Good luck with your research!!!
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I want to use the silica solution in UV-Vis spectrophotometer
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Distilled Water.......
Tracking production of aniline with UV/Vis?
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The research group I'm a part of is looking to track the rate of generation of aniline (or the disappearance of a urea group) during a Retro-Diels-Alder reaction. We can track the progress of this via NMR but it's rather cumbersome and we'd love it if there were an easy way to attach some groups to make the aniline traceable via UV/Visible Spectroscopy.
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Aniline itself absorbs in the UV-Vis. You can prepare mixtures of your reaction products and use a chemometrics approach together with UV to solve your problema. Once you have made your calibration system, all you need is to withdraw a small simple of your reaction at preestablished times, dilute your simple and read its absorbance; an alternative is to add an internal standard and do GC or GC-MS to your samples.
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I have some sediment samples and I would like to characterize them by reflectance spectroscopy in the visible and near infrared range. However, there are some factors influencing the sediments spectra, i.e. organic matter, texture, minerals and metals.
How could I solve this problem?
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Hello Ismael,
I'm currently working with a portable visible spectrometer (380-730nm) for sediment characterization.
We experienced that water content (and thus organic matter content) may affect to a certain degree the shape,amplitude,slopes of the different spectra.
What about trying to express your data as 1st derivative ?
(Debret et al. 2011.Spectrocolorimetric interpretation of sedimentary dynamics: The new “Q7/4 diagram”-Earth-Science Reviews 109 (2011) 1–19).
This would thus imply not treating your samples which can be of interest !
Sorry for not answering directly to your question.
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I want to measure the cloud point of a solution made of 5% polymer and 95% toluene. The measurements are not repeatable for the same solution. The polystyrene has a molecular weight of 100K. I am using a UV spectrometer with a temperature controller. The wavelength is set at 500 nm. I use a quartz cell with a lid to avoid any solvent loses. Data acquisition starts from zero degrees to 40 degrees. Why are my measurements not repeatable?
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Hello Magda,
I follow your advices, I over heated and stir the solution just as it is described in your paper. My measurements are repeatable. Thank you so much for your help!
Youmna
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I don't know how to fix this bug.
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Dear Melissa,
Yes, I have the same bug with a LS-55 Perkinelmer spectrofluorometer and the software FL Winlab v4.0. The bug is due to a software problem with the file names, if you use simple short names without dots, spaces, etc, to save your spectra you will avoid this bug.
Best regards
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I took UV scans of ethyl oleate (ester of oleic acid) in hexane in a wavelength range of 400 -200 nm. Scans of hexane were conducted to see if it was suitable as a solvent and it was. No absorption shown for hexane between 400 -200nm. However, a scan of ethyl oleate in hexane shows a well defined small absorption peak at 308nm and then from 290nm to 200nm there is sudden increase in the absorption and scattering of the data points. Can anyone tell me why this happens? The same happened for other samples scanned: methyl oleate and oleic acid.
I know that from 200nm downwards, the air also begins to absorb light, but this should be the case from 290 -200 nm?
A picture is attached.
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What is the absolute absorbance? If the y-axis in the figure is the number directly from the spectrometer (the absorbance). It is a bit difficult to tell, but it is possible that very little light is hitting the detector at the lower wavelengths because the sample is strongly absorbing the light. If this is true, what you are seeing is essentially detector noise.
To test this possibility, try diluting the sample (by a factor of 10 - 1000). You will loose the longer wavelength peaks, but the shorter wavelength peaks might come back on scale. There are two pi-->pi* electronic transitions that could be quite intense, large \epsilon value (from the double bond and from the C=O).
If you plot the data as curves rather than point it might help see that.
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Refractive index and thickness of film.
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Good afternoon,
From your data you cannot know both the thickness and the index of refraction even after correcting for the bugs in these data. You can only measure the optical thickness that depends on the wavelength. Only ellipsometry allows for the dual determination for a transparent thin film on a transparent substrate of known index of refraction. The easiest way is to measure the physical thickness first and then to measure the optical thickness that would give you the index of refraction through a simple division.
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The circular shape porous membrane is of 70 micron thick is made up of GNP's and ZnO nanocomposite using vacuum filtration technique onto AAO Al membrane as shown in the attached picture. I wish to investigate the UV-VIS optical properties of the nanocomposite.
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If you want to collect an absorbance spectrum, diffuse reflectance is the best option, since your film looks to have low specular reflection (does not appear to have a mirror finish). If you want to learn more about the material's properties I would suggest variable angle spectroscopic ellipsometry. If you do not have access to the instrument, some instrument companies will run demonstration samples for you to show the utility of the measurement.
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Also, what are the other cheaper methods to study the stability?
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It's pretty straightforward with spectroscopy if you are talking about colloidal spectroscopy. Your spectrum will begin to redshift as aggregates grow and eventually just flat line all together. You can check it by putting some NP's in a uvvis spectrometer and forcing aggregation (one easy way is to add a strong acid to lower the ph < 2)
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I'm doing an enzyme activity assay, PPO (polyphenol oxidase) on the young coconut water (ycw). I didn't extract the enzyme n just used the natural ycw. For the sample I mixed the 5.5 ml of 0.2M sodium phosphate buffer (pH6) with 1.5 ml of 0.2M pyrocatechol and after 5 min of stabilization of temperature I add 1ml of ycw. I read the absorbance at 294 nm. I rezero with the blank (5.5ml 0.2M sodium phosphate buffer and 1.5 ml of 0.2 M pyrocatechol) and read the sample at one minute interval for 30 minutes. However, the values of the absorbance was initially -ve but after 15 to 20 minutes, the absorbance change to +ve value. Besides, the absorbance values for one of the sample are -ve till 30 minutes of the assay. Is it normal? Can anyone give suggestion so I can correct it if what have I done is wrong. I attached here together with the journal I used.
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Likely, when you are adding the ycw,you are diluting the buffer and substrate concentrations so that they are lower than your blank. This will cause a negative absorbance. You need to adjust the final concentrations of the buffer and the substrate to be the same for the blank and the sample (i.e., higher concentrations of buffer and substrate should be added to the sample so that when you add the extra volume of ycw, their concentrations are the same as the blank).
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Less aggressive solvents are preferred.
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Your question is not clear. R u going to do solvent effect or going to take UV for any one of solvent. If one means try CHCl3 or DCM.
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From a journal, the standard calibration curve was prepared from a concentration of 1 to 10g/L. In my experiment, the maximum expected concentration of the solution is 0.1 g/L. Would the concentration value that I get will be accurate if I am using the standard curve?
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Please be careful, the ideas given by others have been useful. But if the reported linear concentration range is from 1-10 g/L, it is possible that the responses obtained between 0 and 1 g/L did not increase linearly with concentration. So if you are going to analyse a sample with a concentration outside the reported linear range, you need to verify that you can get a linear response for concentrations between 0 and 1 g/L. If that is not possible, your other choice will be to concentrate your sample by a factor of 10 or more to come within the reported 1-10 g/L range.
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I have read that, for example, broadening of the absorption spectrum in QD's is due to photobleaching. When an active centre is bleached, why does this cause a broadening into the blue and red band edges? What else can lead to this broadening? Is this only related to effects on dipole transitions etc.?
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In solids samples at room temperature phonon vibrations would cause broadening of luminescence emission. However, at low temperature namely due to absence of thermal phonons, peaks are narrowed down.
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A high band gap calculated from Tauc Plot of metal oxide polycrystalline films is generally composed of absorption from the energy levels of the material and the scattering from the grain boundaries. Taking this factor into account, if one tries to estimate the band gap using only UV-Vis spectroscopy what are the chances of his estimation being wrong? Or more precisely how much (highest) scattering factor contributes in estimation of the band gap from Tauc plot for polycrystalline materials?
I am getting a band gap of nearly 4.05eV for ZnO polycrystalline films (300nm thickess) from Tauc Plot while PL spectroscopy says it to be 3.28eV (both measurements are repeatable and done at multiple sites of the films, after subtracting the contribution of substrate, which is quartz in the present case.)
If I take the difference of 0.77 eV as resulting from scattering then it is quite high to report scientifically. Could anybody here provide me with some literature or suggestions to understand this in a better way?
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Rishi, usually the presence of light scattering in thin films induces the blurring of absorption edge and tunning to the long-wavelength side of the spectrum as well as reduces its steepness. In the case of determining of band gap by approximating of the absorption edge, understates its real value occurs. Photoluminescence spectra make it possible to observe the excitonic emission. If you observe the free exciton emission, it is the energy of its excitation. Bandgap equal to the excitation energy of free exciton plus the exciton binding energy. In the case of ZnO its exciton binding energy is 60 meV. Photoluminescence line at 3.28 еV, which you observe, corresponds to the emission of free excitons (3.276 eV ; see :
http://s-space.snu.ac.kr/bitstream/10371/4909/1/GetPDFServlet.pdf ). Therefore, the band gap of the investigated ZnO polycrystalline films corresponds 3.280 + 0.060 = 3.340 eV, which is in excellent agreement with the value for ZnO bulk single crystals. It means that you have a good optical quality thin film. Tauc approximation is noncorrect determination of bandgap energy. See discussion in RG : http://shootingcupoche.com/profile/Andre_Menezes_de_Oliveira/.
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I have no experience with the process of deconvolution, can anyone help me to do deconvolution of individual measured data (11 individual samples).
For each type of lignins, a stock solution was prepared by dissolving lignin powder in NaOH (0.1 M). UV-VIS absorption spectra were registered using solution of lignin on a CECIL spectrophotometer, absorption region 200 -450 nm, scan speed 5 nm/s and resolution 1 nm. Measured values of absorbance were normalized by absorption maxima for even samples, respective.
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Thanks
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We collect our diffusion reflectance spectra of powders with semiconducting properties and a question came up - if every time when we change the samples we should adjust the optical alignment?
Especially, in the case of background and sample measurements we doubt if the change of sample holder height affects the results significantly. Can anybody please comment how to collect data correctly in order to calculate the bandgap from a Tauc plot properly?
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thanks a lot for your suggestions. We do not have an integrating sphere detector. Hence, I think data collection with the best reflectance signal for each sample is reliable.
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I am interested for the UV spectra of vitamins.
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What is the difference between IR spectroscopy and UV-vis spectroscopy?
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If someone is looking for if a drug is binding the DNA or not which technique should they use?
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Thanks dr mahesh
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As I know, no way to extract the data directly, because usually plots are inserted as raster or vector picture. I suggest to use the so-called graph digitizers: http://digitizer.sourceforge.net/ or http://getdata-graph-digitizer.com/
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In the characterization of polymer electrolyte membrane, what I infer from UV-VIs spectrum?
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If I understand your question properly, you have a "dry" polyelectrolyte membrane and you wish to study its interaction with a solvent (presumably with water). You should chose a membrane thickness where you can measure in as broad as possible wavelength range the UV-Vis spectrum. Then you should soak the membrane in a solvent, take the spectrum again and compare. Red or blue shift of the absorption peaks may tell you something about the nature of interaction. You should study the spectrum of the pure solventas well (in the case on water it is necessarry only beacue of potential contaminants - especially in the case of ion-exchanged water, which may contain organic contaminants). It helps if you study the literature of the spectra of smaller molecules which are similar to the repeating unit of your polymer. It is advisable to repeat the measurements at several pH vlaues as polyelectolytes are very sensitive to the pH (conformational and other changes). It may be worth to try Raman spectroscopy as well, perhaps transmission IR oon films (although water has very strong absorption peaks). It may also be interesting to compare the spectra of polyelectrolyte membranes exposed to various RH% (relative humidity) environments. In the Handbook of Chemistry and Physics you can find a list which tells you the RH% values of various staurated salt solutions. They can be used in exsiccators to generate constant RH% enviroment. It is also advisable to measure the weight change. If you have access toDEA (dielectric analysis, especially boradband one) you may get further information on the polymer-water interaction. Measurement of sorption-desorption curves mayalso prove useful (where probably hysteresis will be observed).