Quantitative determination of 13 C‐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 (GC‐MS) were applied to the determination of the endogenous and 13 C‐labeled β‐carotene, lutein, and retinol in plasma of a subject who consumed kale ( Brassica oleracea ) that had been grown in a 13 CO 2 ‐enriched atmosphere. All compounds were analyzed in the negative chemical ionization (NCI) mode using methane as the moderating reagent gas. β‐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 β‐carotene isotopomers in the plasma over a several‐week period were determined using 2 H 8 ‐β‐carotene as an internal standard. The total plasma concentrations of all trans ‐lutein were quantified by HPLC analysis with a photodiode array detector using β‐apo‐8′‐carotenal as an internal standard, and the ratio of the 13 C∶ 12 C 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 13 C‐and 12 C‐retinol isotopomers were quantified using 2 H 4 ‐retinol as an internal standard. These methods demonstrate the application of highly sensitive procedures empolying NCI MS for the quantitative determination of carotenoids and vitamin A for the purpose of conducting metabolism studies of phytonutrients.