Use of eluent modifiers for liquid chromatography particle-beam electron-capture negative-ion mass spectrometry of carotenoids

Liquid chromatography/mass spectrometry (LC/MS) with a particle-beam (PB) i nterface was investigated as a new method for the analysis of carotenoids. The applicability of this LC/MS technique was evaluated for the determinati on of carotenes (lycopene, beta-carotene) and xanthophylls (astaxanthin, lu tein, zeaxanthin, beta-cryptoxanthin). Reversed-phase separation of caroten oids was carried out using two in-series narrow-bore columns in gradient-mo de; analytes were detected under electron-capture negative-ion chemical ion ization (NCI) conditions. The use of additives (ammonium acetate, triethyla mine) in the LC mobile phase was investigated and the performance of the PB interface was improved in terms of better sensitivity and Linearity. Under selected-ion monitoring NCI-MS conditions the absolute detection Limits of carotenes were in the 0.2-3 ng range, whereas for the xanthophylls it was in the 0.02-20 ng range. To study the effect of the addition of the mobile phase modifiers on the PB-MS behaviour of carotenoids, three-way analysis o f variance with interactions was applied, which provided evidence for a sta tistically significant effect of the additives. By applying LC/PB-NCI-MS, c haracterization of carotenoids in microalgae was successfully performed NCI mass spectra confirmed the identity of some of the carotenoids investigate d; in addition, alpha-cryptoxanthin and echinenone were detected in the ext ract. Copyright (C) 1999 John Wiley & Sons, Ltd.