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

The investigation of p-carotene and the xanthophylls P-cryptoxanthin, lutein, zeaxanthin, canthaxanthin and astaxanthin using reversed-phase liquid chromatography-electrospray mass spectrometry interfaced with TurboIonspray (LC-TurboISP-MS) is described. Two narrow-bore C-18 columns connected in series 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 and the MS detector response were investigated for carotenoids, varying the orifice plate voltage, the ring voltage and the ISP voltage. Both conventional ISP and TurboISP were performed; using the TurboISP-MS system, ionization 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 solution-phase oxidants. Using LC columns and acquiring in single-ion monitoring mode, detection limits were estimated to be in the 0.1-1 ng range; dynamic range was established between one- and two-orders of magnitude. Better sensitivity under positive-ion than negative-ion conditions was demonstrated. (C) 1999 Elsevier Science B.V. AU rights reserved.