Science method

VIS/NIR Spectroscopy - Science method

VIS/NIR spectroscopy is an instrumental method to quantify properties in samples. The technique is based on measuring how much light is absorbed in the sample at different wavelengths, and then uses this information to provide details about, for instance, chemical composition.
Questions related to VIS/NIR Spectroscopy
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Soil scientist with experience in vis-NIR spectroscopy, what would be the loss of quality of texture and organic C models when using equipment with spectral resolution of 5, 10 and 20 nm in the NIR (from 1300 to 2500 nm)? Does anyone know of any scientific study that has tested equipment with different resolutions?
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Good replay
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I have been investigating different options for NIR light sources, such as Tungsten, Tungsten-Halogen (or Quartz Tungsten-Halogen [QTH]), Mercury, and Xenon lamps (continuous and "flash"/pulsed modes). Moreover, there are some narrowband NIR LEDs that can be employed in some applications and I particularly did some tests with such LEDs.
However, I was not able to find a detailed study comparing such optical sources or even expanding the above options list. Clearly, many of these options of light sources seem to be targeting medical applications (e.g., endoscopic instruments), UV applications, and optical microscopy. Therefore, even if the wavelength range reaches NIR, a significant part of the effective optical power of the light source goes to VIS or UV regions which represents a significant disadvantage for the development of energy-efficient NIR devices.
This page is nice source of information regarding selecting the proper lamp for your application, including figures with the spectral responses of different light sources. However, the article does not specifically target NIR applications:
In this another excellent source of information, the manufacturer provides the Spectral Irradiance Data for the light sources they sell:
But, again, the document does not provide a deeper discussion targeting NIR applications + energy-efficiency.
Any suggestions ?
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thanks for your contribution, what experience have you for NIR light with combined Mo S2 molybdenum disulfide in pancreatic cancer treatment
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Dear Researcher, I am new to the field of spectroscopy, I have obtained a NIR spectra of 60 different sample of soil. then I did Wet chemical Analysis and find out the (NPK) concentration in each sample. now I want to link it with the spectra so that i can predict NPK of unknown sample using VIS-NIR. waiting keenly for your answers.
also i looked into many articles and Matlab/Python codes for PLSR, PCR etc. but unable to creat link.
Thank you
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Dear Wali,
Please check this paper:
Any question, contact me.
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Dear researchers,
I am learning how to apply Vis-NIR Spectroscopy to predict soil physical and chemical properties.
I have read many documents related to this research direction. There is heterogeneity in the experimental layout between publications: for example, power of the light source, illumination angle of the light source, the distance between the fiber optic cable and the soil sample surface, etc.
I want to find the optimal performance process to obtain the best soil spectra data.
I look forward to getting your experiences and suggestions.
Best regards,
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Hello, dear Trung, I hope that you are very well
for more information about the protocols of measuring soil spectra using Vis-NIR spectroscopy contact me.
with best regards
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What are the benefits of reduced grain size in window material in solar cells, in regard to optical properties? Is there any possible disadvantage of it?
Reduced grain size increases toughness, strength of a material. Smaller grains offer enhanced ratios of surface area (A) to volume (V) i.e., greater ratio of grain boundary (GB) to dislocations. The more the GBs, the higher is the strength because nano-grain size of thin film produces more GBs between crystal grains. In addition, nano-scale materials have far larger surface areas than similar masses of larger-scale materials. As surface area per mass of a material increases, a greater amount of the material can come into contact with surrounding materials, thus affecting reactivity. Nanostructured window material can exhibit more uniformity. Besides these structural advantages, which optical improvements can be achieved through reducing grain size in solar cell window material? And, how?
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Md. Mahabub Alam Moon You are right that Optical improvements of solar cell windows depends on the grain sizes. There are major optical effects these can affect the performance of a solar cell due to the cell's window grain size such as optical waveguiding and scattering. The grain size within a window does change light propagating direction due to multiple reflections, which could guide more lights into the cell and reduce the scattering. This enhances more absorbed light for the active layer of the cell, thereby improving the efficiency of a cell.
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Does anybody know a database on fluorescent properties of chemical compounds?
There are many papers describing flurescent properties of various compounds. Is there any database on fluorescent properties with a structure search function?
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An emission spectrum in IR wavelength region consists of interference fringes (after spectral correction). How do I smooth such spectra? When collected through fiber, absorption around 950 nm makes the situation worst. Is there any way to smooth or fit it?
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what is the sampling frequency you used and what is the value of the samples N you used to claculate your FFT. Can you enlarge the x axis near the maximum of the M plot? what is the repetition rate of the high frequency oscillations? If you enlarge the spectrum figure you can determine it.
Best wishes
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Please could you recommend best software for spectroscopic calibration. 
So far I was using Unscrambler (working with data-pretreatment, selection of important variables, PCA, PLS, PCR etc. ), but now I'm looking for a software enabling more scientific approach e.g. writing a script, optimization algorithm etc., more variable selection methods, different calibration methods, time series etc.
Can the SIMCA or PLS_Toolbox be a good option?
Thank you.
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if you want, you can try to use my software
It is opensource! You do not need to write any line of code to make your multivariate analysis.
It works on Linux, OSX and Windows 64 bit.
Best regards
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Dear All,
I have developed calibration model and cross-validated for visible near infrared spectroscopy for three soil properties, however, my cross-validation results are very different for R2 for all three properties, for example, my R2 is 0.88 for calibration and 0.48 for cross-validation for one and more or less the same for other two properties, what could be the resason? any idea or suggestions should be appreciated to take into consideration?
Best Regards
Hafeez
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Hi Hafeez,
Probably the reason why you get low R2 in cross validation, is that you model is over fitted. It means, when you build and calibrate your model, the model is over-fitted with the training data. The same case that you get, the model works very well for the training data, but does not for the validation data.
One option that you can try is to better randomization when you chose the observation to train the model.
Best regards,
Daniel Quiroz
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* i have collected soil samples during hyperion pass over the study area and chemical analysis was done.
* Lab spectral signatures has not taken.
* How can i correlate the chemical analysis results to hyperion data after preprocessing?
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You need to model multi-variate regression (PLSR/PCR) between each laboratory obtained soil nutrient data of the sample points, keeping as dependent variable (Y) and spectral reflectance of the sampling points obtained from HYPERION data as independent variable (X). One usually predicts the nutrient value from the relationship between X and Y and cross-validates the predicted value through examining the precision of fit in linear regression between the actual and predicted values of nutrient.
You can learn about the MATLAB implementation of PLSR/PCR from the following link:
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I'm preparing a spatially-resolved oblique diffuse reflectance experiment with the objective of finding the reduced scattering (mu_s') and absorption (mu_a) coefficients of some turbid samples.
My setup is very similar to that described in Hu et al 2017 (DOI 10.1007/s11694-017-9465-x). I have a couple of technical/practical questions related to this experiment, so if you have never done something alike, you might want to skip this one.
I use an optical fiber to deliver the light at a 45 degree angle at the surface of the sample (liquid) and I'm collecting the reflectance with another fiber that moves in a parallel plane to the incidence plane. This is necessary to avoid collisions between the fibers. The liquid and the fibers are separated by a 0.2 mm cover glass.
The two planes are 2.2 mm apart from one another (delta_y). The main paper describing the theory behind this experimental setup is Lin et al 1997 but the authors (as well as other authors that do similar stuff) do not explain how the shift between incidence and collection planes should be handled in terms of modelling. To me it makes sense that this delta_y enters in the definition of the distances (rho_1 and rho_2) used to compute the theoretical reflectance (R), obtained from the diffusion approximation. However, when I plug in all the values into my code to find \mu_eff by fitting my data, I cannot find a stable solution. I have to "artificially" increase delta_y in order to get \mu_eff values near the expected/theoretical ones. Has anyone experienced such problems?
I've tried small adjustments to delta_x (due to possible errors in the light entry point measurement) and different optical coupling parameters (A), but nothing seems to works. Could it be related with the width of the light beam that enters the sample? In my case the projected beam spot in the surface of the turbid sample is an ellipse of 2.1 x 1.4 mm.
If you have any comment/idea about possible sources of error that I'm might be overlooking, please leave a comment. Also I would like to know your suggestions about the best way to normalize the data before doing the fit procedure for this kind of experiment.
I appreciate any help, advice, reference or person contact that could help me move forward with this. Thanks.
Dário Passos
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Dear Eugene and Furkan
thank you for your comments. Regarding my problem, I know that I've done everything by the book into accounting for the delta_y displacement in the geometry of my oblique diffuse reflectance experiment. What I find strange is that almost no one tells how they handle this displacement in their works. I've mails 4 different authors (some with recent publications) and no one replied back... I find that odd. Or they didn't care about the effect or then they didn't thought about it (which I doubt). Nonetheless I would like to hear from someone that had applied this same kind of experiment to find about tips on how to optimize it.
In principle, and according to the literature, the diffuse approximation should be enough to explain the light behaviour in the kind of turbid samples that I'm probing (biological tissues, milk, etc) so no need to go into specific models. However, I admit that some of samples might not be well explained by assuming isotropic scattering as the diffusion approximations relies on. Some food for thought for sure.
Cheers and thanks
Dário
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Although the software that came with the vis-NIR has a colorimetry option, you have to manually record soil color (RGB, CIELAB) for each spectra. I have vis-NIR spectra for over 900 soil samples, and took triplicate scans. It would be awesome if there was an R code I could use to get soil color quickly. Thanks!
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Dear Jennifer, I would like to gently lead you away from R-codes and introduce you to CIE colorimetry. You task of converting your spectral curves into internationally agreed CIELAB co-ordinates may be resolved into a fully automated process using the CIE Standard Observer colorimetry. A full account of this is given by Janos Shanda in Chapter 3 of his book “understanding the CIE system” which is available on-line. See also the (perhaps easier to read) book ‘Billmeyer and Saltzman’s Principle of Color Technology ‘ by Roy S Berns, which is also available on line.
In brief, the CIE Colorimetry Committee specified a series of visual Standard Observer and Standard Illuminant models based on well-founded practical experiments, whose product is in each case is a set of spectral weighting coefficients that specify visual intensity. Your calculation then involves multiplying the spectral power values by both these weighting coefficients and summing the result three dimensionally over wavelength. The resulting CIE XYZ colour Identity co-ordinates are then mapped onto CIELAB values in order to redistribute them more evenly in colour space.
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Is there any upconverting nanoparticles with high quantum efficiency (preferable emission in red), which can be excited using sunlight ( NIR band).
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As stated above by Rupesh Talewar, theoretically there is no physical reason for upconversion to be impossible under solar excitation if excitation intensity is high enough. But to see it, you will definitely need to remove visible part of solar radiation with some filter to be able to distinguish your emission due to upconversion from scattering, fluorescence etc.
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I've NIR and Vis-NIR spectral data. This problem is occurring in both cases.
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Hello Mudassir Arif Chaudhry ., i think you need to use Kennard&Stone algorithm to split your dataset into calibration and validation and test it again. Sometimes this situation really happens, however you need to try other types of split to your data to avoid more optimistic evaluation of your models.
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Hi, I'm currently analyzing a data set obtained from a VIS-NIR spatially resolved diffuse reflectance (SRDR) experiment. The experiment setup is the classic for SRDR measurements, where we have a fixed collimated light beam (white light) focused on the surface of a turbid media and collection optical fiber that collects the spectra at several distances (horizontally). The wavelength range used in the experiment is from 500 to 1150 nm and the target solution is TiO2 white powder (Degussa P25) dilute in water. The solution looks like milk. For individual wavelengths we observe the expected decay of collected light intensity as the distance between fibers increases. First distance used is rho0=16mm and last one is 27 mm (with 18 measured points in between).
My problem is related with the fitting process of the individual wavelength data, Intensity vs distance ( I vs rho) using the diffuse approximation models such as Farrell etal 1992 or Hull etal 1998 and the retrieval of the scattering (\mu_'s) and absorption (\mu_a) coefficients. I'm using a common least square approximation (using python's scipy.optimize.curve_fit ) for the fit but the process seems to be very unstable. I've tried other software packages (Mathematica) but I got similar results.The algorithm seems to have problems distinguishing between the contributions of \mu_s' and \mu_a. It looks like there is some kind of degeneracy in the paramerts. I would expect that the scattering coefficient would monotonically decrease with increasing wavelength but that is not the case. I would also expect that the values for the absorption coefficient would be coherent with the water spectrum for most wavelengths. Again this is what I get.
Has anyone dealt with a similar problem? Any suggestions on how to improve the reliability/robustness of the fitting process? Any advice regarding extra cares to take for the experimental setup? All information is welcome!
Thanks in advance
Dário Passos
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Here, examples of articles considering effect of source-detector distances on optical coefficient retrieval:
-"H. Cen and R. Lu, Optimization of the hyperspectral imaging-based spatially-resolved system for measuring the optical properties of biological materials, (2010) Opt. Express 18, 17412-17432"
-"M.L. Askoura, V. Piron, F. Vaudelle, J.P. L’Huillier, E. Madieta, E. Mehinagic, Experimental investigation on light propagation through apple tissue structures, Proc. SPIE 9542, 954218 (2015)."
-"M. Jäger, F. Foschum, and A. Kienle, Application of multiple artificial neural networks for the determination of the optical properties of turbid media, J. of Biomedical Optics 18(5), 057005 (2013)"
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Dear RG Members,
I'd to know is inferences about soil physical properties (water +granulometry) using RGB +NIR spectrometry is possible?
Thanks in advanced,
ASANTOS
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Yes , surely you can draw better conclusions ...
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Dear all,
I am interested in processing PPG signals with the least possible delay. The high-frequency noise should be removed. Then, the local maxima, local minima and DC component should be computed in order to extract the ratio of ratios (mentioned in "Design of pulse oximeters", section 9.3):
R = ln ( Rmin / Rmax ) / ln ( IRmin / IRmax ),
where Rmin ,  Rmax,  IRmin, IRmax  are the minima and maxima of the red and infrared light intensities.
Which FAST method do you recommend me for this procedure, please? Standard tools in the temporal domain are affected by noise, and spectral domain tools introduce 1 cycle (about 1 s) delay.
Thank you very much in advance.
Best regards,
Fernando
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Thank you Hilal. I've seen some references, and artifact removal is critical. Even with a reasonable bandpass filter there are remaining artifacts. This is discussed e.g. here:
"A Prototype of Reflection Pulse Oximeter Designed for Mobile Healthcare".
Did you process PPG signals? How did you remove or ignore the artifacts?
Thank you in advance!
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I work with solid powder (like silica) and need to study fluorescent properties of it (including quantification).
Who can recommend good lab. practice...and particularly: How to make samples for spectroscopic investigations
1) Shall I dilute sample with other non-luminescent matrix?
2) What is more correct: a) to make tablets (under pressure) or b) record a spectrum from powder?
3) Can I record spectra of suspension in solvent?
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Great, will try.
I don't have light adsorption by matrix because have something like core-shell particles and I afraid that crushing will reveal the core ))   
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I have a light absorbing metal oxide deposited on FTO coated glass. I want to perform a diffuse reflectance measurement and determine the %R for our light absorber only and not the underlying FTO. We are using an Agilent Cary 5000
The way I was taught by a student in another lab is as follows:
1) Get baseline spectrum with BaSO4 standard
2) Perform DRS measurement on the FTO substrate by itself and obtain the %R of  the FTO substrate
3) Perform DRS measurement on the sample (light absorber on FTO) and obtain the %R of the sample
4) Obtain the %R of light absorber only by the operation: (%R Sample)/(%R FTO)*100. To this Kubelka-Munk can be applied and F(R) obtained for the light absorber only
Is this the correct way to obtain F(R) for my light absorbing material?
I get results that I expect but I very much want to be sure I am doing this correctly.
Thank you
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Update for people in the future who find this through a search engine.
We found that trying to remove the FTO background by dividing out the FTO signal (step 4 in original post) will not work. There were cases where we were getting impossible results. We decided to leave the FTO NIR signal in our spectra as that was the most accurate depiction of the data.
It was decided that if we want data without the FTO signal, then we must grow films thick enough that all the light in the DRS experiment is scattered before it reaches the FTO or simply scrape off the film and perform a measurement on the powder.
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Hi,
I have a batch of synthetic ruby that I would like to perform ICP-MS analysis on in order to verify the relative abundance of chromium incorporated into the sample.  I have been unable to find a suitable reference for dissolution of the sample material in the literature (a few journals not accessible for me).  If anyone knows of a suitable way to dissolve this sort of sample, it would be great to find out.
Best wishes,
Martin
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It is extremely difficult to dissolve rubies. This sample treatment should be done by the alkaline fusion in platinum crucible. Try non-destructive XRF or LA-ICP-MS option instead.
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Hello
I am interested in buying a spectrometer for my research. Any suggestions of reasonable priced models that can cover the VIS, NIR and SWIR regions and easy to you and maintain? Thanks
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Thanks for all the comments. I will be shopping soon for the suggested ones. Best regards
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In my previous experiments and talks with my colleagues, this effect has been attributed to (1) incomplete drying of the spot and/or (2) high concentration of salts still in the sample. I'm wondering if there are other factors that can cause this effect. Thank you
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 Thanks. Prof. Kadhum.
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I want to calculate the percentage content of water/ moisture present in human hair through Near Infrared Spectroscopy. any addition method has to be applied after spectra determinations to calculate exact / approximate water content ? 
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If they dont describe the exact amount of moisture content, then what information/ parameter do we get from NIR for hair fibres? is it possible to determine the same from any other technique ?
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Does anyone knows how to open/run DPT files (NIR spectroscopic data) in The Unscrambler software?
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Step 1 : rename  .dpt to .txt
Open it in .txt and replace all comma (,) with 5 spaces (     ) and save it
Step 2: Now replace all . with , and save it
Step 3: Open it in origin.
Goodluck!
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Hello everyone
I have developed a compact spectrometer (photo attached) and working towards developing it into a milk analyzer. I will be using 600-1100nm, based on literature, where researchers have used this range to quantify the fat% in milk. 
Before beginning, I would like to make sure how the calibration could be transferred from one device to another. There are some products available already in the market like Foss Milkoscan, but they use mid-infrared wavelength range, making it less challenging to transfer calibration. Others like Fatscan, haven't yet made it to the market.
Is it impossible? Can someone please elucidate the actual challenge in scale up while transferring calibration? Any leads would be appreciated.
Thanks.
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What are you going to calibrate, wavelength or transmission (absorption)?
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I was following the standard protocol given by Spectralon® to clean. But organic dyes are not able to eliminate because it is not soluble in water. So can we use some organic solvents to clean. (it should not effect by organic solvents) or please provide some technique to clean or remove dyes from the standard.
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I would like to try to control the content or concentration of active principle in a liquid mixture inside a plastic infusion bag. At the same time i would like to monitor if the API is what we are expecting inside the bag. Have someone some experience in this measurement? I'm thinking to do transmission measurements instead of reflection measurement.
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What is your API and its concentration?  Remember, NIR is weak radiation so you will get a weak response!
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Hi guys, I am in need of FT Raman spectrometer for non-destructive quality assessment of fruits. I found a few of the instruments in my vicinity but they all need sample to be prepared. But I need an instrument that can give me the spectra of the fruit without breaking it. Kindly let me know where the instrument available.
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There is an excellent review article in the Encyclopedia of Analytical Chemistry (John Wiley & Sons, Ltd). The title is "Fourier Transform Raman Instrumentation", author Edwards, Howell G. (see the link below). In this article you will find a number of examples of non-destructive FT Raman measurements (mummies, paintings, etc.).
Apart from this I agree with Hugh: why use FT Raman when cheaper (handheld?) dispersive Raman could perform the same task?
Please send an e-mail in case of no access to the paper.
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I am wondering if there is any spectrometer to measure spectra in 100-200 nm range, and how one can get access to this facilities?
Thanks in advance
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McPherson is providing al lot of V-UV spectroscopy equipment. And they know where their customers are:-) Just contact them: http://mcphersoninc.com/
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Wavelength test - Fail,Noice test - Fail, Bandwidth test - Pass.
Kindly help me to interpret following results who's having a FOSS NIR machine.
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Dear Prabhani,
I suggest for you a links and attached files in topics.
-Support Vector Machines and Their Application in Chemistry and ...
-Feed and Forage Analysis with FOSS
-NIRperformance.com - NIR for the feed industry
-Fast feed analysis with NIRS DS2500 Feed analyzer - FOSS
-Feed and Forage Analysis with FOSS
Best regards
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A small pocket NIR from SCIO can cheaply scan intact leaves from the small Arabidopsis as well as from big leaves as Vitis Berlandieri or Bananas. This instrument is able to discriminate the two pages.
In different cultivars of grape in the inferior page are concentrated more or less some cotton-like formations.
The 1st question is:
Are these hairinesses related to polyphenols ?.
The 2nd question is:
how polyphenols are ontogenetically related to the leaf maturity (sum of the components crude fiber, NDF, ADF, Lignin, crude protein, lipid, ash, free sugars ) till to senescence and death?.
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1. question
I have not yet read about the relation between hairnesses and polyphenols. Maybe in literature it can be found. May be using sone instrumental analytic techniques gives some clues about it look at some phenol derivations whether exist or not in hair part of it by HPLC or other cromatographic instruments. sometimes GC-MS can be more suitable detect  gimmenic acid, flavone, hyroquinone or gallic acid.
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Just need to generate continuum removed spectra from the reflectance data.
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Pls use the continuum removal function in Envi. First you should start the "plot" window and plot your spectral curve.
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Hi, I am looking for some commertially available or "easy-to-make" material that has an absorption peak in visible 400-550 nm, emission peak (or tail) in near-infrared 800-1700 nm and lifetime in order of picoseconds.
Need it to measure the instrument responce function of my TCSPC setup.
Thank you.
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Yes, they are embedded in silicon layer (were grown by molecular beam epitaxy) so actually silicon is absorbing visible light and transfer energy to Ge QDs. 
At least spectra for 445 and 532 nm excitation wavelength look similar.
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I'm using the NIR-spectrometer model PT-IM100 from Pharma Test. The glass vial will be filled with the solid samples for measuring by NIRS. To perform a measurement with paste or liquid samples, the Aluminum stamp should be put in the glas vial.Why can't the liquid sample be measured without using the metal stamp (like the solid samples) ?
Thank you
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Dear Dr. Kuptsov,
Thank you very much for your clear and helpful explanation. As far as I've understood the Instrument measures the liquid samples by transmittance-reflectance mode. 
After measuring a sample, the plot of reflectance against wavelengths will be shown but it is also possible to change the parameters in the Software in order to get the plot of absorbance or transmittance against the wavelengths. In other words, I can get different plots ( different y-axis) according to adjusted parameters in software. When I have a Plot of for example absorbance against wavelengths, is the measuring mode  still reflectance ?
Regards
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 I need to quantify amino groups on the suface of treated PTFE.IR spectroscopy in the region of 1100 to 1800 nm shows the peak in 1400 nm which seems to be relavant to first overton N-H or O-H  stretching bands.(our system works in this range of wavelenght-1100 to 1800 nm).How I can distinguish between the first overton N-H and O-H stretching bands to see whether or not this peak is relavant to N-H?
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hi,
OH groups can be derived by gazeous treatment by SF4 or NO so as to deconvolute the overall absorption band.
regards
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How can I prepare powder samples for Perkin Elmer UV/VIS/NIR spectrometer?
Do I need some special kind of sample holder because in chemistry they usually use it for liquids samples? and my samples are rare earth phosphate glasses. Is dissolving these powder in liquids give me best result or should I use solid sample (Powder or piece)? if I use solid/ powder, how to use it in spectrometer.
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Any compound ( or matter)  soluble in water may be easily analysed by UV-Visible  spectroscopy.  One can get quartz cell  where the aqueous solution is placed with fixed or even unknown concentration of the dissolve impound. If it is a double beam machine then one has to calibrate the zero line ( to make back ground adsorption oat minimum)  and this is done by placing  water in two  matched cuvettes  ( quartz cells normally of 1 cm  x 1 cm  size cross section ) and  scanning the  blank water from from say 200 nm to 1100 nm . In this way one can suppress the back ground absorption. Once this is done the sample holder containing pure water is to taken out and the water is thrown and then the desire compound whose electronic spectrum ( Uv-Visible) to be measured in aqueous solution is to be placed in this cuvette. Be careful, first rinse the cuvette with little solution you wish to measure. Do it thrice and then pour say 2.75 mL of the aqueous solution into this cuvette ( normally of 3 mL capacity )  . Place the cuvette filled with your test solution in to  the sample holder  and run the machine. . You can get the entire spectrum of the sample in water. Record it and then analyse the absorption peaks .  One should know to analyse the  absorption peak by its nature , intensity etc. For a new compound these peaks are electronic signature. Thus for a known compound with know concentration dissolved in water the peak position and the electronic spectra will be conserved , therefore this is used for analytical purpose.  A suspected compound can be tested with its electronic ( UV-visible)  spectrum and if it matches with the known spectrum of that solution in the same solvent then one can identify the compound . If your water sample contains more than one compound then you should know the individual electronic spectrum of each suspected compound.  In that case you will get a composite spectrum. The electronic  absorption is additive. That means if two compounds are having very similar spectra then one has to deconvolute the spectrum to get the individual contribution. Crudely speaking both the  pure compounds can be mixed in different proportion to record several spectra. And  if such a spectrum with mixed composition matched with the observed  spectrum of the water sample then one can say that the water sample contains these two compounds in the ratio that was measured while creating the aqueous solution of both the compounds. One can do several such thongs and these are available in books and in several publications . Hope this helps you  
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  1. Standards for plotting calibration curve is biggest challenge for NIR method development, any body can give suggestion.
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But apart from OH end group rest of the molecule matrix always get change in our sample so NIR calib curve is strictly OH+Matrix of entire polymer chain depedent, so how we can overcome this problem. 
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NIR spectroscopy data provide transmittance or absorbance spectrum data in the range of NIR waves. The data is 'continuous' data with peak and valley on certain range of frequency/wavelength depend on characteristics of sample. Can we apply data mining techniques for modeling or correlate this spectrum data with other physico-chemical data and how to do that? 
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for very useful tutorials have a look here  https://www.youtube.com/user/QualityAndTechnology
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How to choose the best method between IR/FT-IR and NIR/FT-NIR spectroscopy for quantitative analysis of pharmaceutical substances?
Thank you so much for your answers.
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Dear Mrs/Ms Kazemi,
I fully agree with Mr. Kira and Mrs./Ms. Ivanova. It is a good starting point to compare your product with the pure substances and there are different methods with advantages and disadvantages.
Raman scattering is generally suited for aqueous solutions, because you are working with visible light (water is a very strong absorber in the mid-IR range), but it can be used for solid samples, too. Unfortunately, you have to employ very intense laser radiation, that can affect/damage sensitive samples.
IR can also be used for aqueous samples, but the sample thickness and concentration has to be adjusted carefully. For powders you can either make a KBr pellet and measure in transmission mode or you can employ attenuated total reflection (ATR). For the latter you need only a very small amount of sample, which can be used further afterwards. You can also let your sample solution dry on the ATR crystal.
For a concentration determination I would make KBr pellets out of your pure substance using different concentrations and compare it with your sample.
The question whether NIR or mid-IR range is better depends on your sample. Generally I prefer mid-IR, because the transition energies are lower, and hence, the peaks are narrower and less overlapping. On the other hand, samples can be opaque in the mid-IR range, while they are transparent in NIR, but you can compensate the less transmittance by adjusting the sample concentration or thickness. Or you perform a reflection measurement.
Modern FT-IR spectrometer can be adjusted the preferred spectral region. Why do you not use both (NIR and mid-IR) and compare afterwards?
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I performed the quantitative calibration (PLSR method) by NIR Spectrometer (Pharmatest IM 100) to measure  the concentration ( in range of 0.02-0.5 mg/ml) of Resveratrol  als drug in an Ethanol-Water (1:2) solution . The value of  Multiple correlation coefficient is 0.96 and standard error of estimate is 0.05. I performed the Prediction for new known solution to test the  calibration but the result is totally unacceptable and there is a big difference between the predicted values and the actual values and there isn’t any chance of prediction. 
I guessed maybe the calibration is overfitted and I tried to carry out the calibration again by smaller range of Wavelength but the result was the same, any one have an explanation?
Hope someone can help me.
Thank you in advance for your answer.
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WOW its hard to measure ingredients in those concentrations... usually concentrations less than 0.1% are undetectable... what kind of software did you use? did you really get the coefficient of correlation (r-sqared) or did you get the coefficient of determination (R-sqared)? nevertheless a value of 0.96 is excellent.
To answer your question:
1st: prediction vs lab result is NOT prediction vs. true value, because the lab results include some reasonable errors of measurement. Your RMSECV can't be better than the error of analysis of lab results.
2nd: for concentrations > 1% NIR spectroscopy is a good method, for 0.1 to 1% you have to deal with the right conditions such as temperature control, defined sample length a.s.o.
3rd: did you take a look at your spectra? did you perform some data preprocessing? such as 1st and 2nd derivate? please do so and take a close look whether they are similar at some absorbance bands which should lead to a (very small) difference in spectral characteristics. in absorbance spectra themselfes you won't see a difference, maybe in 2nd derivate is a difference.
but algorithms like pls may extract some information that you're not able to "see" in the spectra...
- which wavelength range did you use for measurement?
- which wavelength range did you use for calibration?
- usually you have 1, 2 or 3 absorbance bands of water (-OH) in your spectra --> low signal, high noise --> dont use it for calibration
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I found 2 characteristic peaks at 204 nm and 251.5 nm in the UV-Vis spectrum of the ethanol solution hold inside the turned-yellow (old) PE bottle for about two weeks. After that the bottle turn white, look much better than the initial state. I suppose that the degradant was extracted into the ethanol solution. One peak at 204 nm is similar to characteristic peak of pure BHT. I wonder if the second peak 251.5 nm is characteristic for the degradant of BHT or for certain substance that makes the bottle yellow. Who can tell me something about this peak?
Thanks in advance.  
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Dear Peter Kapusta!
Thanks for your interest in my question. From the literature, I've known that BHT is widely used in production of LDPE bottle as antioxidant.  I specially run the spectrum of ethanol solution of pure BHT, and  observed the characteristic peak at 204 nm, consequently, it's asumed as the characteristic peak of BHT. How about your opinion? Looking forward to hearing from you.
Best regards!
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I have some transparent or semitransparent meshlike fabrics to analyse using my VIS NIR (400-1000nm) and SWIR (1000-2500) scanners. I need to use some black (strong absorbing) material as background to eliminate additional signal.
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the question is not simple, I asked also to some colleagues. This is the result:
- You may put a sheet of heavy black cloth. Because there are not "reference" clothes, you should first test it with the scanner.
- you could use a black paints as those used for optical instruments on satellites but i do not know trade names. Also in this case, preliminary tests are necessary.
good luck
perla
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Hi Researchers,
Good morning/afternoon/evening. I'm reaching out to all of you seeking information.
Could you all suggest good articles/reviews on the current state of in-line & off-line analysis of polymers using FTIR/Raman/NIR spectroscopy?
Thank you and looking forward to the responses.
Best Wishes,
Arindam
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Hi Arindam,
 There is an entire book on Vibrational Spectroscopy of Polymers edited by Everall, Chalmers and Griffiths. Also Prof. Heinz Seisler has worked on and published extensively in this area. 
Are there particular polymers that are of interest?
Regards,
Katherine
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I'm calibrating NIR for SBM, Guar korma, FFS,Corn and animal feed? Resently we got SBM with high fibre. But NIR didn't give real value.
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What kind of regression you are using in order to associate NIR spectrum and lab-determined values? Normally, Partial Least Square Regression method works fine.
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I used 780 nm excitation with 100 mW power laser of Raman to analysis reduced grapheme oxide. I found that most of research used UV and visible excitation for graphite based material analysis. What's the difference of G band position shifting which excited by different wavelengths? Does NIR-Raman spectroscopy can be used to distinguish the content of sp2 and sp3?
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Yes, although not optimal, you may use this wavelength for your Ramans studies. Just be careful when comparing your results with published ones, as indeed most people use visible excitation for doing the same. The G band should not move, but D and D' bands will be shifted significantly. Also the intensity of the G band depends on the wavelength. Therefore, the intensity ratio of D/G bands will be totally different from other papers, but correlation with wavelength exists, see the attached paper.
Alain
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I am going to scan seeds by NIR spectroscopy. However, since there is some resin in berries, I would like to know how to clean off the resin from the seeds and which solvent I should use so that it doesn't influence the spectra?  
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If you need only to know how the spectrum from seeds looks like, you can mechanical collect some resin , take a resin spectrum and subtract it from the spectrum of "impurity" seeds.
Alternativ, you can use the same treatment protocol for all your measurements. Although the solvents affect the resulting spectra it will be done on the same way in all experiments.
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I collected the NIR spectra over some samples using a hyperspectral camera and a handheld spectroscopy sensor in same conditions. I found there are differences between both spectra from the camera and spectroscopy. I used least square matching between them, but it didn’t work. In the following figure you can see the spectra from three different samples. Solid lines are hyperspecral spectra.
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Dear Ata,
I think it will be very difficult to find a way to link the two due to very different instrumentations. Indeed, you have different bandwidth, different signal to noise ratio and often differences of the analyzed volume.
Even, if you use a derivative to suppress baseline shift you will observe different spectral contributions.
Regards.
Ludovic.
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In a dark room
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Is the question about the camera being able to "see" the particular wavelength? If "yes", simply look at your laser spot on the camera's screen. Most commercial cameras sensors see somewhat above 1 micron.
Or is the question about how to capture short laser flash with your camera? Dark room, the smallest diagram, the longest exposure ...
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Preprocessing methods in NIR spectroscopy.
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Dear Rassol,
This book can be good for you :
Near-Infrared Technology: In the Agricultural and Food Industries (from Phil Williams and Karl Norris). 
Editor: Amer Assn of Cereal Chemists; Édition : 2 (novembre 2001)
ISBN-10: 1891127241
ISBN-13: 978-1891127243
Regards.
Ludovic.
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A membrane consists of excipients and solvents blended together.
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I think it is possible, in principle. The devil is in details.
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I can normally measure free zinc in alkaline solution by using ICP-OES.
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For Mdm. Esma Senel
<p> It is to bring to kind observation that that Zn(II) can also be  estimated spectrophotometrically by  another equally efficient method. But here the complexing ligand first need  to be prepared in the laboratory.Of course, once prepared, it can be kept to use  time and again.</p>
<p>[A]General procedure for the preparation of ligand :</p>
<p>1.0 g of 3-Hydroxybenzaldehyde is dissolved in 25 mL of double distilled water and mixed in a flask with 1.0 g of 4-aminobenzoic acid and refluxed for 3 hrs. A pale yellow colored crystal product having the formula  3-hydroxybenzylaminobenzoic acid   formed. After filtering the product, it was dried at room temperature.Finally the very light colored product was recrystallized by using ethanol(M.pt=165C; yield=80-90%).</p>
<p>[B] Now  prepare a standard solution of zinc sulphate solution containg 3.3 μg/ml of Zn(II) ions . Take 25 mL of this solution and to it add about 75 mL of buffer solution[pH(5sodium acetate-acetic acid buffer)]  and 50 mL of the ligand solution[ prepared by dissolving  20 mg of the ligand was dissolved in 100 ml of chloroform] . Keep for sufficiently long time to obtain  yellow colored hydroxybenzylaminobenzoic acid -zinc complex. </p>
<p>[D]The mixture solution is shaken vigorously in a separating funnel. It was extracted</p>
<p>with  over a total of 80-90 ml of chloroform(3 times). The  organic layer was transferred in 250 ml volumetric flask  after keeping over anhydrous calcium sulphate for sufficiently long time. Filter the chloroform layer to obtain  the  complex in the nonaqueous layer.</p>
<p>Then follow the steps E-K  [as given in the first method]  while using  460 nm filter.</p>
<p> </p>
<p>The complex remains stable for over 12hrs.</p>
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I am taking NIR spectra on wood sections and I would like to know if the spectra are crossing through the 5 mm samples.
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Thank you RJ Blakey!
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.
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If you are looking for FTIR. Thermo Scientific produces very reliable ones.
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I need to characterize (spectro-polarimetric analysis) 980nm laser diodes.
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Thank you Sh. Nizamov for your reply. I think I finally found a good camera for my apllication (with a price / quality ratio that seems to me excellent). It is a Photonfocus camera (MV1-D1312I) equipped with a CMOS NIR enhanced sensor.
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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 using vis-NIR to measure soil samples and calibrate spectral data to predict unknown samples (those of samples have reference value from lab chemical analysis). After I get prediction results from NIR measurement, I want to use prediction error (such as RMSEP or SEP) from NIR to compare error from lab chemical analysis. My question is does it have any principal for this kind of comparison, and how to calculate lab error?
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An important point has to be considered performing a calibration of an NIR-system. The major method error of the NIR-method is due to the error of the reference method, because the accuracy of the NIR-method is the sum of the reference error and the error of the NIR system. While the repeatibility (repeated measurements on the same sample with same device and same people) of the NIR-system is realy small the main error source is most often the reference method. And if you would like to compare the accuracies you should not compare the repeatability of the reference method with the SEP of the NIR system. The better comparisson is to compare reproducability (same sample - in case of destroying measurement nearly same sample, different devices from same type, different location and different people) with NIR-accuracy because this is also a different device. Additional it is very important for the accuracy of the NIR-method not to mix the reference methods, e.g. not to mix drying oven and moisture analyzer.
Recommendation: Check reproducability of the reference methods and take into account this error number for the evaluation of the NIR-method.
To check the lab performance you could do the following:
You have to check the precision (repeatability) and reproducability of the reference method.
1) A sample has been measured with NIR take and divide into 5 parts and divide each resulting sample again into 2 equal parts.
2) performe reference method on a set of 5 in house or your standard reference laboratory (important vary the name of the 5 samples randomly) so that no inference possible to the origin of each 5 samples) => Repeatability
3) send the second 5 pieces to a 2nd refernce laboratory . Compare the average value mean value obtained in 2) or compare the error sum of individual differences => Reproducability
4) Compare Repeatability and Reproducability with the NIR error (SEP). Presumption NIR difference to the average values ​​of the two 5-measurement is smaller (maybe the same) as the standard deviation of the two reference multiple determinations. => NIR is a method that works within the error limits valid reference.