13] Atmospheric pressure chemical ionization and electron capture negative chemical ionization mass spectrometry in studying β-carotene conversion to retinol in humans

Abstract

This chapter proposes a method that uses flow injection atmospheric pressure chemical ionization–mass spectrometry (FI/APCI–MS) to measure the enrichment of β-C-d8 in the serum of a subject who was orally supplemented with β-C-d8. The kinetics of the metabolism of β-C-d8 to retinol-d4 is investigated using gas chromatography–mass spectrometry with electron capture negative chemical ionization (GC/ECNCI–MS) to measure the enrichment of derivatized retinol-d4 in the serum. Under APCI conditions, β-C is readily ionized by proton transfer from protonated ethanol to a protonated molecule with a molecular mass of 537 Da. β-C analyzed by APCI–MS exhibits a linear correlation between concentration and signal response. The APCI analysis for β-C extracted from a blood sample is presented as replicate flow injection profiles. The detection limit was 50 pg of standard β-C. The absolute concentration of labeled β-C-d8 in serum reached 329 nM in 2 days after the administration of β-C-d8 while unlabeled β-C-d8 in serum peaked at 1 day after the β-C-d8dose. The highest enrichment of labeled β-C-d8 was 30.9%, which occurred at 2 days after the β-C-d8 dose.