Quantitative determination of 13C-labeled and endogenous β-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 (CC-MS) were applied to the determination of the endogenous and C-13-labeled beta -carotene, lutein, and retinol in plasma of a subject who consumed kale (Brassica oleracea) that had been grown in a (CO2)-C-13-enriched atmosphere. All compounds were analyzed in the negative chemical ionization (NO) mode using methane as the moderating reagent gas. P-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 H-2(8)-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 C-13:C-12 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 CC-MS in the NO mode. The C-13- and C-12-retinol isotopomers were quantified using H-2(4)-retinol as an internal standard. These methods demonstrate the application of highly sensitive procedures employing NO MS for the quantitative determination of carotenoids and vitamin A for the purpose of conducting metabolism studies of phytonutrients.