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Niklas Warne (Niklas)
Posted on Thursday, November 20, 2003 - 3:37 am:   

Hi,

Does anybody have any information whether it is possible to determine the amount of crystalline water in various matrixes using NIR?

Also, is possible to distinguish between amorphous and crystalline sugar with NIR?

Regards
Niklas
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Gabi Levin
Posted on Saturday, November 22, 2003 - 8:55 am:   

hi Niklas,

I assume you mean "bound water" that actaully bonds by complexation bonds to the d or f orbitals of the cations in the crystal. These usually have different wavelength of absorption from free water, because the vibration is affected by the additional bonding. This is typical in clay, where the bound water peaks at about 1390nm vs. 1450nm for free water. I have done work on clay and it is a text book example if one wants to write a text book.

In principle, all bound water will differ from the free water in their peak position. The degree of difference depends on the specific crystaline structure, and the cations involved.

Actual experiment, by using hydrated crystals, introducing moisture and following the cahnges in absorpion as you dry it gradually. The peak that will remain unchanged under normal drying conditions (100 or less degC) will tell you where the bound water are.

With organic crystals the situation is more complex, and I will not venture into it unless you specify this to be the case.

About amorphous vs. crystaline sugar, I did not try it, but since the OH bonds are in specific order in space, and in amorphous they should be arbitrarily oriented, I wold expect spectral differences. Definitely worth studiyng, let me know what you have found. If you send to me at Brimrose samples of amorphous and crystaline sugar (ground to same level of particle size roughly to eliminate this effect) I will be glad to run spectra and see what we can learn.

Thanks,

Gabi

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