Automated coupling of capillary-HPLC to matrix-assisted laser desorption/ionization mass spectrometry for the analysis of small molecules utilizing a reactive matrix.

Abstract

This study describes the application of a novel, reactive matrix for the mass spectral analysis of steroids by capillary-high performance liquid chromatography (capillary-HPLC) coupled to matrix-assisted laser desorption/ionization (MALDI). The mass spectral analysis of steroids was accomplished after fully automated peak deposition of chromatographic peaks onto MALDI targets. The seven corticosteroids used as test compounds were: triamcinolone, prednisone, cortisone, fludrocortisone, dexamethasone, deoxycorticosterone, and budesonide. They were separated using a PepMap C(18) (3 microm particle size, 100 A pore width) column at five different concentration levels of 25, 15, 7.5, 2.5 and 1 ng/microL, and the peaks were detected at a wavelength of 237 nm. The column effluent was mixed with 2,4-dinitrophenylhydrazine (DNPH) directly following the UV detector. The chromatographic peaks were then deposited onto the MALDI target with a robotic micro-fraction collector triggered by the UV detector signals. A special hydrophobic surface coating allowed the deposition of up to 4 microL (up to 90 % of the chromatographic peak volume) onto one sample spot. The compounds were then identified by MALDI mass spectrometry. Depending on the nature of the analyte, radical cations ([M](+.)) and sodium adduct ions ([M+Na](+)) of the steroids as well as protonated steroid-dinitrophenylhydrazone derivatives ([M(D)+H](+)) were detected in positive ion mode. The detection limits were between 0.5 and 15 ng injected with capillary-HPLC-MALDI-TOF-MS and between 0.3 and 3 ng on target with MALDI-TOF when deposited manually.