Liquid chromatography-electrospray mass spectrometry of beta-carotene and xanthophylls - Validation of the analytical method

The investigation of p-carotene and the xanthophylls P-cryptoxanthin, lutei n, zeaxanthin, canthaxanthin and astaxanthin using reversed-phase liquid ch romatography-electrospray mass spectrometry interfaced with TurboIonspray ( LC-TurboISP-MS) is described. Two narrow-bore C-18 columns connected in ser ies and an isocratic solvent system containing acetonitrile-methanol (0.1 M ammonium acetate)-dichloromethane at a flow-rate of 300 mu l/min (without splitting) were used. Operating in the positive-ion mode over mit 500-650, the effects on the formation of the molecular ion species or adduct ions an d the MS detector response were investigated for carotenoids, varying the o rifice plate voltage, the ring voltage and the ISP voltage. Both convention al ISP and TurboISP were performed; using the TurboISP-MS system, ionizatio n efficiency increased with respect to ISP-MS, particularly at the highest temperature (500 degrees C). Good results were particularly obtained for p- carotene, which was detectable at the low ng level, without the use of solu tion-phase oxidants. Using LC columns and acquiring in single-ion monitorin g mode, detection limits were estimated to be in the 0.1-1 ng range; dynami c range was established between one- and two-orders of magnitude. Better se nsitivity under positive-ion than negative-ion conditions was demonstrated. (C) 1999 Elsevier Science B.V. AU rights reserved.