Fully on-line hyphenation of an experimental OPLC separation unit with diode-array detection and mass-spectrometry (OPLC-DAD-MS) for analysis of xanthine compounds

Abstract

Summary The newly developed experimental OPLC separation unit 100 (OSU 100) has been used for fully on-line multiple hyphenation using the one-channel flowing eluent wall (FEW) arrangement at the inlet. OSU 100–UV and OSU 100–DAD–ESI–MS with manual injector or autosampler were used to test the connected systems (OPLC–UV; OPLC–DAD–ESI–MS), using xanthine standards (caffeine, theophylline, theobromine) and green tea leaf extract as model compounds. The mobile phase chloroform–trifluoroacetic acid–acetonitrile–methanol, 76:4:6.67:13.33 (v/v) is suitable for rapid and selective separation, DAD, and ESI–MS of xanthines. The detection sensitivity of OPLC–UV or OPLC–DAD was increased by hyphenation with ESI–MS coupled in series. In contrast with DAD, the extracted ion chromatogram (m/z = 181.1 Da) after background subtraction yields readily measurable peaks from the small amounts of theophylline and theobromine in tea leaf extract. Analysis of xanthines was achieved within 10 min with less than 2 mL mobile phase. Owing to the openable adsorbent layer in OPLC the bed conditions can, moreover, be checked off-line after single or multiple fully online separations.