Determination of sterols using liquid chromatography with off-line surface-assisted laser desorption/ionization mass spectrometry

• Published in: Journal of Chromatography A 2014-09, Vol.1358, p.102-109
• Main Authors: Vrbková, Blanka, Roblová, Vendula, Yeung, Edward S., Preisler, Jan
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Fat industries; Food industries; Fundamental and applied biological sciences. Psychology; Off-line coupling; Oil sample; RPLC; SALDI MS; Silver nanoparticles; Sterols
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2014.06.077

•Off-line coupling of HPLC and desorption mass spectrometry for nonpolar compounds.•Silver nanoparticles used as matrix for efficient ionization of sterols.•A laboratory-built spotter employed for the coupling.•Sensitivity adequate for analysis of important constituents of food.•An alternative to on-line GC–MS or LC–MS for analysis of nonpolar compounds. A new method, reversed phase liquid chromatography with off-line surface-assisted laser desorption/ionization mass spectrometry (RPLC–SALDI MS) for the determination of brassicasterol (BR), cholesterol (CH), stigmasterol (ST), campesterol (CA) and β-sitosterol (SI) in oil samples has been developed. The sample preparation consisted of alkaline saponification followed by extraction of the unsaponificable fraction with diethyl ether. The recovery of the sterols ranged from 91 to 95% with RSD less than 4%. Separation of the five major sterols on a C18 column using methanol-water gradient was achieved in about 10min. An on-line UV detector was employed for the initial sterol detection prior to effluent deposition using a laboratory-built spotter with 1:73 splitter. Off-line SALDI MS was then applied for mass determination/identification and quantification of the separated sterols. Ionization of the nonpolar analytes was achieved by silver ion cationization with silver nanoparticles used as the SALDI matrix providing limits of detection 12, 6 and 11fmol for CH, ST and SI, respectively. Because of the incorporated splitter, the effective limits of detection of the RPLC–SALDI MS analysis were 4, 3 and 4pmol (or 0.08, 0.06 and 0.08μg/mL) for CH, ST and SI, respectively. For quantification, 6-ketocholestanol (KE) was used as the internal standard. The method has been applied for the identification and quantification of sterols in olive, linseed and sunflower oil samples. The described off-line coupling of RPLC to SALDI MS represents an alternative to GC–MS for analysis of nonpolar compounds.