Determination of enantiomeric compositions of amino acids by near-infrared spectrometry through complexation with carbohydrate.

A new method has been developed for the determination of enantiomeric compositions of a variety of compounds. The method is based on the use of the near-infrared technique to measure diastereomeric interactions between an added carbohydrate compound with both enantiomeric forms of an analyte followed by partial least-squares analysis of the data. The fact that the method works well with all three macrocyclic carbohydrates with different cavity size (i.e., alpha-, beta-, and gamma-cyclodextrin) as well as with sucrose, which is a linear carbohydrate, clearly demonstrates that it is not necessary to have inclusion complex formation in order to produce effective diastereomeric interactions. Rather, a simple adsorption of the analyte onto a carbohydrate is sufficient. Since inclusion complex formation is not a requisite, this method is not limited to the amino acid studies here but is rather universal and sensitive as it can, in principle, be used to determine enantiomeric compositions for all types of compounds with only microgram concentration and enantiomeric excess as low as 1.5%, in water or in a mixture of water and organic solvent. Furthermore, it does not rely on the use of rather expensive carbohydrates such as cyclodextrins but is equally as effective even with a simple and inexpensive carbohydrate such as sucrose.