ONLINE TRACE ENRICHMENT IN HYPHENATED LIQUID-CHROMATOGRAPHY NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

The potential of on-line trace enrichment combined with column liquid chromatography-nuclear magnetic resonance detection (LC-NMR) is demons trated for the identification of hop bitter acids in hop extracts. By performing on-line solid-phase extraction on 1-5 ml of hop extract (wh ich contains the six major hop bitter acids) the detection/analysis ti me in the stopped-flow detection mode could be reduced 4-fold, from 60 min to 15 min per individual peak. The applicability of combined trac e enrichment and separation using a single short (12.5 mm x 4.6 mm I.D ,) high-pressure-packed column combined on-line with MMR was also stud ied. Sample enrichment of 5 mi of a solution spiked with three drugs a t 5 mu g/ml was sufficient for the acquisition of high-quality spectra both in the stopped-flow and even in the continuous-flow detection mo de. The examples demonstrate that analyte detectability can be signifi cantly improved by performing on-line sample enrichment prior to LC-NM R analysis. (C) 1998 Elsevier Science B.V. All rights reserved.