Analysis of Herbal Products by GCMS using TMS Derivatives

The recent growth in the neutraceutical field has presented new challenges for analytical laboratories. There are new products coming to market all the time, and determination of their active ingredients can be very complex.

Traditional methods for these types of samples include colorimetric tests and HPLC analyses. However, these have potential drawbacks. Colorimetric tests, such as those used to determine hypericin in St. John's Wort, are prone to interference and can be compromised by deliberate adulteration. Even HPLC separations can be insufficient in determining active ingredients, due to the complexity of the product and the non-specific nature of UV or RI detection.

We have been developing a new approach to some of these problems, involving derivatization and GCMS analysis. Traditional GC analyses of many of these formulations is difficult or impossible, since many compounds of interest are not sufficiently volatile or thermally stable to make GC practical (such as sugars), while others are detectable, but are still difficult to chromatograph (such as low molecular weight organic acids). Even if these obstacles can be overcome, GC is still subject to the same problems with non-specific detection as HPLC.

Derivatization can solve many of these problems. Many of these compounds have active hydroxyl groups as part of their structure. While these make the compounds difficult to GC, it makes them easy to convert to trimethylsilyl ethers or esters. This process increases their thermal stability and volatility, making them amenable to GC or GCMS determination. Because of the complex nature of many of these products, we have found GCMS to be more practical. As an example, this chromatogram shows the determination of citric acid in a cranberry extract. GC analysis would not be possible, due to the co-elution of citric acid with sugars. GCMS, however, can monitor for the characteristic ion at m/z 273, easily distinguishing the citric acid from the surrounding sugars. This also demonstrates the flexibility of the technique, detecting carbohydrates and acids in the same analysis. Other compounds could be included as well, such as flavonoids.

We are currently developing this technique with a variety of compounds, including carbohydrates, acids, flavonoids, and other difficult compounds such as ellagic acid and quercetin. If you have any specific applications you would like us to investigate, give Mike Shelton, Dr. Jack Northington or Eric Lindsay call.

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Formerly West Coast Analytical Service (WCAS) and Bodycote Testing Group