title: Sodiation as a tool for enhancing the diagnostic value of MALDI-TOF/TOF-MS spectra of complex astaxanthin ester mixtures from Haematococcus pluvialis.
abstract: The microalga Haematococcus pluvialis produces the pigment astaxanthin mainly in esterified form with a multitude of fatty acids, which results in a complex mixture of carotenol mono- and diesters. For rapid fingerprinting of these esters, matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF/TOF-MS) might be an alternative to traditional chromatographic separation combined with MS. Investigation of ionization and fragmentation of astaxanthin mono- and diester palmitate standards in MALDI-TOF/TOF-MS showed that sodium adduct parent masses [M + Na](+) gave much simpler MS(2) spectra than radical / protonated [M](+●) / [M + H](+) parents. [M + Na](+) fragments yielded diagnostic polyene-specific eliminations and fatty acid neutral losses, whereas [M](+●) / [M + H](+) fragmentation resulted in a multitude of non-diagnostic daughters. For diesters, a benzonium fragment, formed by polyene elimination, was required for identification of the second fatty acid attached to the astaxanthin backbone. Parents were forced into [M + Na](+) ionization by addition of sodium acetate, and best signal-to-noise ratios were obtained in the 0.1 to 1.0 mM range. This method was applied to fingerprinting astaxanthin esters in a crude H. pluvialis extract. Prior to MALDI-TOF/TOF-MS, the extract was fractionated by normal phase Flash chromatography to obtain fractions enriched in mono- and diesters and to remove pheophytin a, which compromised monoester signals. All 12 types of all-trans esterified esters found in LC were identified with MALDI-TOF/TOF-MS, with the exception of two minor monoesters.
authors.affiliation: Wageningen University, Laboratory of Food Chemistry, P.O. Box 8129, 6700, EV, Wageningen, The Netherlands.
authors.forename: Yannick
authors.initials: Y
authors.lastname: Weesepoel
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Vincken
authors.forename: Raluca Maria
authors.initials: RM
authors.lastname: Pop
authors.forename: Kun
authors.initials: K
authors.lastname: Liu
authors.forename: Harry
authors.initials: H
authors.lastname: Gruppen
mesh_terms: D000460:Chlorophyta / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D004952:Esters / Q000032:analysis / Q000737:chemistry; D010936:Plant Extracts / Q000032:analysis* / Q000737:chemistry*; D011166:Porphyrins / Q000032:analysis / Q000737:chemistry; D059629:Signal-To-Noise Ratio; D012964:Sodium / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods; D024341:Xanthophylls / Q000032:analysis / Q000737:chemistry
chemical_list: D004952:Esters; D010936:Plant Extracts; D011166:Porphyrins; D024341:Xanthophylls; C005948:astaxanthine; D012964:Sodium
keywords: Flash chromatography; Haematococcus pluvialis; RP-UHPLC-ESI-MS; carotenoid; sodium adduct