VITAMIN-D DETERMINATION USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH INTERNAL STANDARD REDOX MODE ELECTROCHEMICAL DETECTION AND ITS APPLICATION TO MEDICAL NUTRITIONAL PRODUCTS

The selectivity and sensitivity of high-performance liquid chromatographic analysis for the determination of vitamin D3 and D2 content in medical nutritional products were improved with the aid of electrochemical detection in internal standard-oxidation/reduction mode. The relative standard deviation at the 13-nmol level for the analysis of vitamin D in products was 3.6% (n = 5). Recovery rates of added vitamin D3 were 97.5 +/- 3.0% (mean +/- S.D.). It is concluded that this method is much more selective and accurate for detection of vitamin D at the nanomolar level than ultraviolet detection methods.