Solid-State 13C NMR of Herbal Supplements
Solid-state 13C NMR is an excellent way to investigate what chemical functionality is present in herbal supplements. The large resonances at 60-105 ppm are due to cellulose/polysaccharides and some sugars. The peaks in the 0-60 ppm region are aliphatic carbons in fatty acid chains. Peaks in the 110-140 ppm region are alkene and aromatic carbons, while peaks in the 140 ppm and 150 ppm region are due to substituted aromatics and phenolic carbons. Peaks in the 160-200 ppm region are due to carboxylic acids, esters and amides. Solid-state NMR is a relatively simple technique that involves no sample preparation and observes the sample carbon chemistry in it’s entirety. The analysis reveals relative amounts of chemical functionality that can be utilized for product-to-product comparison or batch-to-batch manufacturing comparison. The chemical specificity of the technique also means that adulterants can readily be detected and identified.
A few examples of “off the shelf” herbal supplements are shown below.
Figure 3: 13C CP-MAS NMR of Valerian Root Extract, Ginseng Extract, Saw Palmetto Extract, Grape Seed, and St John’s Wort.