| Author | Message | |||
     Dr.K.Balasubramanian (drkbala) Advanced Member Username: drkbala Post Number: 21 Registered: 9-2006 |
Capabilities of near-infrared spectroscopy to analyse changes in water bonding during honey crystallisation process International Journal of Food Science & Technology 2009, 44, 519-524 Slawomir Bakier Abstract: To characterise the changes occurring in honey under the influence of crystallisation process near-infrared spectroscopy has been used. The technique involved analysing the same type of honey by subtracting its crystallised spectrum from the liquid spectrum. The comparison of the difference spectra made it possible to determine specific water bonding processes affected by crystallisation. The surface area under the peak obtained during absorption by water was in the range of wavenumber 5330 to 4965 cm−1 with the maximum at 5155 cm−1. It was found out that the area under the peak was directly related to water activity changes that occurred in honey during the crystallisation process. A regression equation between the area under the peak and water activity assumed a linear form characterised by a high value of the determination coefficient R2. | |||
| Dr.K.Balasubramanian (drkbala) Intermediate Member Username: drkbala Post Number: 20 Registered: 9-2006 |
This problem is there for years and we also questioned the KF agent.But this is purely due to the Humidity of Surface.But when u add water to pur sample this would be normal | |||
| Dr.K.Balasubramanian (drkbala) Intermediate Member Username: drkbala Post Number: 19 Registered: 9-2006 |
This looks to be surface water that is absorbed by the layer in the room where the test is taken.If humidity control is made then there is a possibility of avoiding this.Since I have worked earlier in Purification of Acetonitrile in1994 I had the same problem.Then I used the dehumidifier area so that we got this problem sorted out. | |||
| Don Burns (burns) New member Username: burns Post Number: 5 Registered: 1-2006 |
Claudia - In case you missed Tony Davies' note of Feb 28th, there's another source: "FT-NIR Atlas" by Michael Buback & Hans Peter Vogele, published by VCH about 1993. See spectrum #55. Don Burns | |||
| Howard Mark (hlmark) Senior Member Username: hlmark Post Number: 224 Registered: 9-2001 |
Claudia - there are two main compendia that I know about. The first is the somewhat older "Atlas of Near-Infrared Spectra" published by Sadtler. That's out of print, but you may find a library that has a copy. There is a much newer collection of spectra assembled by Jerry Workman, and published by Wiley, entitled "Handbook of Organic Compounds". It's a three-volume set that includes spectra in the near infrared as well as other spectral regions. \o/ /_\ | |||
| claudia cosso (claudietta) New member Username: claudietta Post Number: 1 Registered: 3-2009 |
can you help me to find a good library for NIR peaks? | |||
| R_A_Forbes |
Folks, I'm using transmission NIR (1 mm path) to quantify trace water in acetonitrile (ACN). When I set up my calibration curve I used ACN dried over molecular sieves. Interestingly, the dry ACN showed two bands (1904, 1922nm) prior to addition of water. The bands both grow when water is spiked. The intercept of the calibration curve was about 0.6%, which would be the estimated water content of the dry ACN. The plot thickens: Karl Fischer analysis of the dry ACN indicated non-detectable water (less than 0.01%). Careful preparation of samples in a dry nitrogen atmosphere, to test adsorption of water during prep., did not reduce the water bands in the dry ACN. I did NMR on the samples as a referee method, and no water was detectable in the dry ACN, in agreement with KF analysis. What is going on? Regards, Bob Forbes | |||
| Bruce H. Campbell (Campclan) |
Bob, It sounds to me that you may have bound water. If that is so, the NMR probably wouldn't pick it up and if the water is bound tightly enough or be released very slowly from whatever it is bound to, the Karl Fischer titrations wouldn't either. The question then becomes what would the water be bound to? How about very small particles of the molecular sieves that were not removed? Bruce | |||
| hlmark |
Rob - there's another possibility that I can think of: the structore of acetonitrile is CH3-CN, which you wouldn't ordinarily expect to have any -NH or -NH2. But if the acetonitrile has impurities from side reactions during its synthesis, you might just find some -NH and/or -NH2-containing molecules. The fundamental bands in the mid-IR for -NH species are not too far off from those for -OH, so it's a reasonable step too consider that the NIR bands are also close to those for -OH, i.e.: water. So in this scenario, what's showing up as a small amount of water is actually the absorbances due to some -NH or -NH2 from the acetonitrile, which may not be as pure as you'd like. Howard \o/ /_\ | |||
| Tony Davies (Td) |
Bob, I had been thinking about purity but see that Howard has (as usual) got there first! There is a spectrum of acetonitrile in the FT-NIR Atlas (Buback & Vogele, VCH) which shows the same peaks. The 1922nm peak is much narrower than the 1904 nm peak. It would be really interesting if we could see your spectrum. Would there be a general interest in the ability to put spectra etc on the site? It would have to be by e-mail via me. The other thought is did you try the quantitation on the 1400 nm water peak? Does it agree with the Karl Fischer? Best wishes, Tony | |||
| Karl Norris |
Bob, I can't explain your results, but I would also suggest looking at the other OH bands of water in the 1450, 1150, and 960 nm regions. This would require the use of longer pathlengths to obtain good signal to noise spectra, but if you see water spectra at all of these bands it must be water. Good luck, Karl | |||
| Lois Weyer (Lois_Weyer) |
Bob, How about the cell itself? What is being used as a reference - air? air in the cell? If the cell has been included in the reference, perhaps the correction for the small amount of water in the cell window is not perfect due to a refractive index change. Suggestions: 1) if the cell is not being referenced, try it 2) if the cell is being referenced, try dry carbon tetrachloride in the cell during the referencing. Lois | |||
| hlmark |
Karl's intuition is generally more reliable than anybody else's scientific analysis, but given the conflicting results, I wouldn't want to draw a conclusion until I had a spectrum of a known-dry, known-pure sample of acetonitrile to compare against, even in the short-wavelength regions. If we are in fact seeing some sort of -NH in one place that appears to be water, we can'r rule out the possibility of bands in other places that could be mistaken for water also. Howard \o/ /_\ | |||
| Art Springsteen (Artspring) |
As an old (and I'm getting to be that!) synthetic organic chemist, we used to worry about contaminants in acetonitrile. Have you tried bubbling dry nitrogen through your sample before you measure it? I also think Lois might have a point- it could be you are seeing water bands in your cell. Good luck, Art S. | |||
| R A Forbes |
Folks, Thanks for all the good suggestions. I�ve emailed copies of the spectra to those who responded to the question. To answer some of your questions: The instrument is a single beam and I�m using the empty cuvette as the reference. For the sample prepared in the dry bag I used nothing in the holder (i.e. air) as the reference, since I had filled the cuvette already when I needed to take a reference. This did not make a difference except for the need to do a baseline correction of a constant offset. The impurity hypothesis is interesting. It seems too coincidental that the impurity has the same two peaks, shape and maxima as the spiked water. The ACN is high purity, HPLC grade. The NMR scan did not indicate significant impurities (I suspect 0.6% could be observed). Examination of the 1400 nm region is interesting. A similar set of peaks is observed in the dry ACN. When water is spiked in, the peaks grow, but the shape looks different. Could there be some absorbance bands from acetonitrile itself that coincide with the water bands? Regards, Bob Forbes | |||
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| R A Forbes |
Problem Solved: Tony Davies suggested spiking the dry ACN sample with deuterated ethanol. If the peaks were due to water, they should move due to deuterium exchange. If not due to water, the peaks should not move. I did not have deuterated ethanol, but deuterated methanol worked. Upon mixing 50/50 D-4 methanol with ACN, the 'apparent water peaks' remained unmoved. To verify they would move if due to water, I spiked water into this sample. Immediately a peak grew due to D2O. Therefore, I conclude the 'apparent water bands' must be due to ACN itself or an impurity other than water. I will send spectra to those interested. Thanks Tony for the help! Regards, Bob Forbes | |||
| Suresh kumar. B (Sureshkumar) |
bob, i would like to see the DryACN Spectrum | |||
| R A Forbes |
Suresh, Send me your Email address and I will send a powerpoint file with the spectra. Regards, Bob Forbes | |||
| Suresh kumar. B (Sureshkumar) |
hi Bob, thanks and Email id is [email protected] or [email protected] regards suresh | |||
| Lois Weyer (Lois_Weyer) |
I realize that this "problem" has been considered solved, but I came across something today related to this that might interest the group. I ran a spectrum of IPDI (isophorone di-isocyanate)and it had a nice peak at 1922 nm. It has no water in it as water would react immediately I've been told. I calculated that either summing the NCO peak at 2260 cm-1 plus a CH stretch at 2950 cm-1 or 2x a CH bending at 1450 cm-1 plus the NCO peak would result in a NIR peak at about 1920 nm. So the triple bond of acetonitrile's nitrile group could easily be combined with CH absorptions to produce a peak near 1920 nm, and probably a doublet. I have not seen this discussed in the literature, but it makes sense to me. Any comments? | |||
| hlmark |
Lois - Combination bands usually require the vibrations to involve atoms that are at leat attached to the same atom. I'm not sure how the N-N triple bond would interact with anything else strongly enough. I suppose you would have to analyze the relative absorbances to start with, before you could even make hypotheses. Howard \o/ /_\ |
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