Clinical and analytical evaluation of the simultaneous HPLC assay of retinol and alpha-tocopherol

Simultaneous analysis of circulating 25-hydroxy-vitamin D3, 25-hydroxy-vitamin D2, retinol, tocopherols, carotenoids, and oxidized and reduced coenzyme Q10 by high performance liquid chromatography with photo diode-array detection using C18 and C30 columns alone or in combination

Circulating lipid-phase micronutrients (LPM) such as 25-hydroxylated D vitamers, retinol, tocopherols, carotenoids including their isomers, and coenzyme Q10 play important roles in health maintenance and disease prevention and can serve as useful biomarkers. We developed fast, affordable, and accurate HPLC assays that simultaneously measured all above LPM in a single run using UV/VIS detection at 265nm, 295nm, and 480nm with (1) a C18 column alone; (2) a C30 column alone; or (3) each of these columns connected in series. The C18 column alone could separate all major LPM of interest in less than 17min but insufficiently resolved the lycopene isomers, the 25-hydroxylated D vitamers, lutein from zeaxanthin and β- from γ-tocopherol. The C30 column alone separated all LPM of interest including many isomeric analytes but failed to resolve the Q10 compounds, which co-eluted with carotenoids. Connecting the C18 and C30 columns in series with a detector after the C30 column and a pressure resistant detector between the columns resulted in ideal resolution and accurate quantitation of all LPM of interest but required software capable of processing the acquired data from both detectors. Connecting the C18 and C30 columns in series with exclusively one detector after the C30 column resulted in carotenoid-Q10 interferences, however, this was remedied by heart-cutting 2D-LC with a 6-port valve between the columns, which resolved all analytes in 42min. Faster run times led to some analytes not being resolved. Many variations of these methods are possible to meet the needs of individual requirements while minimizing sample material and turn-around-times.

A validated liquid chromatography method for the simultaneous determination of vitamins A and E in human plasma

A fast (15 min) and simple HPLC method for determination of all-trans-retinol and alpha-, gamma- and delta-tocopherols in human plasma has been developed. The assay utilized 200 microl of plasma to which 20 microl of internal standard solution (retinol acetate) was added followed by 200 microl of water, 400 microl of ethanol and 800 microl of hexane. The hexane layer was collected, evaporated, the residue dissolved in 200 microl of methanol and analyzed on a Zorbax Eclipse XDB-C18 column using a step gradient with a polar organic mobile phase composed of acetonitrile and methanol and variable wavelength fluorescence detection. The quantification limits for all-trans-retinol and gamma-tocopherol were 20 ng/ml and for alpha- and delta-tocopherols 500 ng/ml and 10 ng/ml, respectively. The procedure was validated and applied to the analysis of plasma samples from the Baltimore Longitudinal Study of Aging.

Stability of fat-soluble and water-soluble vitamins in artificially prepared, vitamin-enriched, lyophilized serum

Vitamin-enriched, lyophilized serum (VES) was prepared for an inter-laboratory study to compare vitamin assays. The VES contained water-soluble vitamins (vitamin B1, vitamin B12, vitamin C, and folate), fat-soluble vitamins (vitamin A and vitamin E), and cholesterol. We performed stability studies and determined vitamin concentrations and total cholesterol in VES stored at -20 degrees C for 12 months. Our recovery of the water-soluble vitamins in reconstituted VES was 70-142%, but we recovered only 33-45% of the fat-soluble vitamins. Physicochemical properties, such as specific gravity and viscosity of the reconstituted VES did not affect manual or automated measurements of these vitamins. Vial-to-vial differences found for the VES were the same as the within-day analytical variations. There was no evidence of degradation of vitamin A, vitamin B1, vitamin B12, vitamin C, folate, and cholesterol over 12 months in VES stored at -20 degrees C. Following deproteinization, vitamin C concentration was found to be lower than when not deproteinated. Vitamin E was less stable in VES, however, and the degradation during 12 months was lower than the between-day analytical variation of the assay. Our VES is the first preparation of lyophilized control serum that contains water-soluble and fat-soluble vitamins.