Over the past few years, Exova has added analysis for several vitamins to our capabilities. The bulk of this work has been on USP nutritional supplements, using the methods described for these supplements in USP 23. However, these methods cannot always be applied to other products. Beta-carotene, especially, is prone to problems.

USP specifications for nutritional supplements do not allow the presence of other carotenoids, such as lutein or zeaxanthin. However, many products on the market, such as herbal preparations, do include these types of compounds. Since they are chemically similar to beta-carotene, they co-extract with the beta-carotene when using the USP methods and interfere with the colorimetric determination. This yields results which are biased high, sometimes drastically. To overcome these problems, we use a modification to the USP method to accurately determine beta-carotene in non-USP formulations.

We have also identified problems with riboflavin analysis. The USP method to determine riboflavin in nutritional supplements is a liquid chromatography procedure. However, to analyze riboflavin raw material or injection, a fluorescence method is used which has presented problems. It requires a sample preparation step using potassium permanganate and hydrogen peroxide without specifying the concentration of these reagents. (Although the permanganate is listed as "1 in 25," this concentration is too strong for the color to be destroyed by the peroxide in the time given in the method. The peroxide concentration is not given at all.)

When we attempted this method, we encountered a problem with the fluorescence measurement which we traced back to the permanganate/peroxide step. When that step was eliminated, the method performed as expected. Because of these problems with the fluorescence method, we have explored using the liquid chromatography method to determine lower levels of riboflavin, such as those found in injectable preparations, and even cell culture media. Although the nutritional supplement method determines riboflavin at levels of 100 ppm in solution, we have found that we can accurately measure it at concentrations down to 0.1 ppm, using the same conditions. We recommend using these conditions to determine low levels of riboflavin. These condition can also determine niacin (or niacinamide), pyridoxine, and thiamine in the same analysis. However, since detection is by UV absorbance at 280 nm, the method can be subject to interferences, especially in complex matrices such as culture or fermentation media.

Please contact us to find out more about our Vitamins by USP Methods capabilities.