Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2007
Publication Date: 9/15/2007
Citation: Wolf, W.R., Atkinson, R. 2007. Determination of Vitamin C in a LC/DAD Method for Analyzing Water Soluble Vitamins in Multi-Vitamin Dietary Supplements Containing Multi-Minerals. AOAC Annual Meeting, September 15, 2006, Minneapolis, Minnesota.
Technical Abstract: We have recently reported a method for the simultaneous determination by liquid chromatography with diode array detection of a suite of water soluble vitamins in multi-vitamin/multi-mineral dietary supplements (MV/MM) (1). In that work, although there was good extraction of vitamin C and good chromatographic separation from other vitamins, we were unable to quantitate Vitamin C, under the compromise conditions used for the other vitamins, due to the instability of the Vitamin C extracts. The extracts rapidly lost detected intensity (within minutes), due to the presence of the multi-minerals in the MV/MM, which catalyzed oxidation of the vitamin C. Standard solutions and extracts of MV tablets without MM were stable. We have successfully modified the conditions of the assay to allow inclusion of Vitamin C in the suite of analytes in this multi-vitamin method. We have rigorously degassed the solvent, lowered the extraction pH to 2.0 from 3.0 and most importantly added a thermostated sample chamber to the LC autosampler, with the temperature set at 4 degrees C. This gives us solution stability of the sample extracts for up to 6 hours, very sufficient to allow a chromatographic run and quantitative determination of the Vitamin C along with the other vitamins. Adding EDTA to the extract to bind the minerals was not helpful in stabilizing the solution, and added more problems with co-eluting peaks for other vitamins. With this method we were able to achieve results for a representative MV/MM dietary supplement table of 63.0 mg/tablet (nominal value 60) with a RSD of 2.4% and recovery of 101% of added vitamin C.