Liquid Chromatography/Mass Spectrometry of Carotenoids Using Atmospheric Pressure Chemical Ionization

✍ Scribed by van Breemen, Richard B.; Huang, Chao-Ran; Tan, Yecheng; Sander, Lane C.; Schilling, Alexander B.

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 676 KB
• Volume: 31
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/(sici)1096-9888(199609)31:9<975::aid-jms380>3.0.co;2-s

✦ Synopsis

Carotenoids contained in plant extracts were analyzed using liquid chromatography/positive-and negative-ion atmospheric pressure chemical ionization mass spectrometry (LC/APCI-MS) with a narrow-bore C,, reversedphase high-performance liquid chromatographic (HPLC) column and a gradient solvent system containing methanol-methyl tert-butyl ether-ammonium acetate a t a flow rate of 300 pl min-'. In addition to mass spectrometric detection, photodiode-array UV/visible absorbance detection was used between the HPLC column and mass spectrometer for additional carotenoid characterization. Positive-ion APCX produced protonated molecules and molecular ions for both xanthophylls and, unexpectedly, hydrocarbon carotenes; and during negative-ion APCI, M-' and [M -HIions were observed. In order to investigate the origin of the unexpected [M + H ] + ions, positive-ion APCI of &carotene was investigated using deuterochloroform as the only solvent. Because fJcarotene formed primarily deuterated ions, IM + D ] + , during APCI in deuterochloroform, the mobile phase was determined to be the source of hydrogen for protonation. The hydroxylated xanthophyll lutein fragmented during positive-ion APCI to eliminate water from the protonated molecule and form the base peak of m/z 551. Using collision-induced dissociation in the ion source, additional fragmentation pathways characteristic of tandem mass spectra of carotenoids were observed such as retro-Diels-Alder fragmentation, [ M -561 +', for a-carotene and loss of toluene from the molecular ion, [M -92]+' for lutein, a-and b-carotene. The limits of detection for protonated molecuies of a-carotene and lutein were approximately 3 and 13 pmol, respectively. In negative-ion APCI, the limits of detection were approximately 3 and 1 pmol for M-' ions of a-carotene and lutein, respectively.