Liquid chromatography-particle-beam mass spectrometric determination of β-carotene by negative-ion chemical ionization

Abstract

The first method for liquid chromatography-particle-beam mass spectrometry (LC-PBMS) of β-carotene is described. It uses a reversed-phase (RP) HPLC column and methanol-dichloromethane, 90:10, as mobile phase. For comparison purposes, UV-visible detection was performed at 436 nm to determine linearity, sensitivity and precision; the absolute limit of detection of the LC-UV method was estimated to be 0.2 ng. The possible modes of ionization of β-carotene were explored for PBMS detection; the best selectivity and sensitivity were obtained by use of electron-capture negative-ion chemical ionization (NCI). When operating in NCI mode with selected ion monitoring (SIM), the detection limit was 0.3 ng for β-carotene, comparable with that of the UV detector. The relative standard deviation (RSD) of the LC-PBMS system was 2.6 % at the 10 ng level (n=10). For the determination of β-carotene in real samples absolute calibration and calibration by the method of standard addition were used for both UV and PBMS detection.