On-line solid-phase extraction in microcolumn-liquid chromatography coupled to UV or MS detection: Application to the analysis of cyanobacterial toxins

An on-line technique coupling preconcentration via a microprecolumn with mi crocolumn-liquid chromatography (micro-LC) on a 1-mm inner diameter (i.d.) analytical column was investigated. The system was found to be very simple, fast, and efficient for the trace-level determination of some natural hepa totoxins synthesized by Cyanobacteria, namely, microcystins, in environment al water. Particular attention was paid to band broadening, and a good qual ity coupling was obtained. A cleanup was introduced in the solid-phase extr action (SPE) sequence to eliminate part of the interferents co-extracted du ring the sample percolation. The technique was reproducible, with relative standard deviations ranging from 3 to 8%, linear in the range 0.05-50 mu g/ L. Microcystins could be detected below the 0.04 mu g/L level in drinking a nd surface water using only 5-mL sample volumes, with UV detection. The ver y small sample volume, resulting from lower detection limits, in absolute a mounts, obtained in micro-LC represents a definite advantage over on-line c lassical chromatography. The suitability of on-line micro-SPE-micro-LC-MS w as also evaluated. Application to the determination of microcystins in envi ronmental and drinking water samples are presented. (C) 2000 John Wiley & S ons, Inc.