| Author | Message | ||
     thomas ricour (tricour) Member Username: tricour Post Number: 11 Registered: 2-2006 |
Hello, could be esaier to use nm instead of cm-1 for NIR peaks. Concerning wines, i try to collect max information about experiences on, and results done in NIR. I'm open to discuss about it. Tom | ||
| Luca Vicenzutto (vice) New member Username: vice Post Number: 12 Registered: 1-2004 |
Sandra, using my experience I try to suggest you to check NCO groups around 5316 1/cm. Regards | ||
| Sandra Helena da Silva Siqueira (sandra_helena) New member Username: sandra_helena Post Number: 1 Registered: 1-2007 |
Is there anyone who could send me a table of the absorption frequencies of the main bonds in the NIR ? Actually I am trying to understand where the NCO groups can be seen to a polyurethane material. Thanks | ||
| Riccardo De Cesare |
Is there anyone who could send me a table of the absorption frequencies of the main bonds in the NIR ? It would really be helpfull to have a scan of an aliphatic isocyanate. Actually I am trying to understand where the NCO and the iscyanurate groups can be seen. Any info is highly appreciated . Thanks Riccardo | ||
| Luca Vicenzutto (Vice) |
Hi Riccardo. I'll search in my files in order to find a table regarding the absorbption frequencies. I'll keep you informed Rgds Luca | ||
| Lois Weyer |
Riccardo, send me your e-mail address and I'll send my chapter on band interpretation. The NCO is a separate issue, though. I don't think I mentioned it in the chapter, but I have been looking at it myself and will try to find you something on it and send it. I should have an aliphatic isocyanate scan also. Can you read an NSAS file? What about GRAMS spc? | ||
| Lois Weyer |
My e-mail address is [email protected]. | ||
| Riccardo De Cesare |
Lois , my address is [email protected]. No idea about my capabilities to read NSAS or GRAMS file. Isn't it possible to send your scans in excel format. Anyway just try and I'll find a way to read it. Last chance could be a "print-screen" in your mail. Thanks Riccardo | ||
| hlmark |
Lois - I think you should also send Riccardo the data in JCAMP-DX format. Both GRAMS and NSAS (and Unscrambler, for that matter) can export that, and even if Riccardo doesn't have a JCAMP reader, since the entire file is ASCII he can extract the spectral data with any text editor (even NOTEPAD). Howard \o/ /_\ | ||
| hlmark |
I guess what questions like this really need is for someone, probably in academia, to undertake studies like the ones done in the mid-IR 50 years ago or so, where isotope replacement studies and other such advanced tools can be used to really pin down issues such as where various functional groups, and individual vibrations, absorb. Howard \o/ /_\ | ||
| gianluca |
Dear collegues, I would like to know the peak of sucrose, fructose, glucose and nitrogenum for a liquid solution of pulp of the beet. Can someone help me? | ||
| hlmark |
Gianluca - not sure what nitrogenum is, but all the sugars basically lose their spectral characteristics when dissolved in water. There is some spectral signature due to their interaction with the water itself, that cause distortions of the water bands, but the nice spectra you see in the solid sugars disappear. Howard \o/ /_\ | ||
| Michel Coene (Michel) |
I did a test on separating several sugars from a catalytic inverter some years ago and, as Howard points out, it is far from easy. You will need a lot of luck and fancy algorthms like LWR on a 300+ spectra calibration set to get anywhere near usuable. Once dry however they are quite easy to separate spectrally. You just need to compensate for particle size (MSC, SNV,...). Getting a good (vacuum) oven might be the best solution! I put the vacuum there because I remember fructose is a #$**!!! to dry ;-) | ||
| Gabi Levin |
Michel is so right. The major issue as pointed out is that the difference between the sugars vanishes. I also did a short study when I was still naive, and I found out that you can prpeare mixtures, with the desired range of variation, and get beuatiful regressions for all three sugars, but when you look at the loadings, you see they don't use any different data for all three regressions, in fact, they are mirror curves, telling us that there is not true distinction. The practical problem is that the models will not predict right, except the sum total of all predicted sugars will be correct. Thanks, Gabi Levin | ||
| NIRguy |
It sounds like NIR has trouble to calibrate different types of sugar in water solution? Can anyone provide more information about that? I remember once read somebody used NIR spectra of four-sugar aqueous solution as dataset to show the improvement their calibration method made. The result is a kind of suspicious though. Y Liu | ||
| Gabi Levin |
Short time ago we had a discussion on sugar in solution. I hope Bruce can provide the information some how to you. Shortly, it was said that all sugars loose all the beautiful peaks once they dissolve in water. Myself, when new and naive tried it on prepared solutions. Calibrations were perfect, but, when you examine the loadings you wil see that there is perfect mirror shape, telling you it will never predict right, because it doesn't realy know who is who. Thus, the sum total of the sugars was always correct, but not the individual ones. Thanks, Gabi | ||
| Bruce H. Campbell (Campclan) |
Gabi and others, I don't know which particular exchange you are thinking of. However, the way to search the archives is go to the URL, NIRpublications.com. When there, look on the left side of the page. A search function is listed that can be used to find words, etc, in the archive section. This should work. Bruce | ||
| NIRguy |
Thanks Gabi and Bruce! I should have done more search before this question jumped out of my mind. YLiu |