Quantitative determination of 13C-labeled and endogenous beta-carotene, lutein, and vitamin A in human plasma

Quantitative procedures employing liquid-chromatography/particle beam-mass spectrometry (LC/PB-MS) and gas chromatography-mass spectrometry (GC-MS) were applied to the determination of the endogenous and 13C-labeled beta-carotene, lutein, and retinol in plasma of a subject who consumed kale (Brassica oleracea) that had been grown in a 13CO2-enriched atmosphere. All compounds were analyzed in the negative chemical ionization (NCI) mode using methane as the moderating reagent gas. Beta-carotene and lutein were analyzed using LC/PB-MS applying reversed-phase high-performance liquid chromatography (HPLC) separation procedures to resolve the analytes. The concentrations of the beta-carotene isotopomers in the plasma over a several-week period were determined using 2H8-beta-carotene as an internal standard. The total plasma concentrations of all trans-lutein were quantified by HPLC analysis with a photodiode array detector using beta-apo-8'-carotenal as an internal standard, and the ratio of the 13C:12C isotopomers of lutein was determined by PB-MS. The retinol isotopomers were collected from individual HPLC fractions of the plasma extract and then analyzed as the trimethylsilyl ethers by GC-MS in the NCI mode. The 13C- and 12C-retinol isotopomers were quantified using 2H4-retinol as an internal standard. These methods demonstrate the application of highly sensitive procedures employing NCI MS for the quantitative determination of carotenoids and vitamin A for the purpose of conducting metabolism studies of phytonutrients.