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 microcolumn-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 hepatotoxins synthesized by Cyanobacteria, namely, microcystins, in environmental water. Particular attention was paid to band broadening, and a good quality coupling was obtained. A cleanup was introduced in the solid-phase extraction (SPE) sequence to eliminate part of the interferents co- extracted during the sample percolation. The technique was reproducible, with relative standard deviations ranging from 3 to 8%, linear in the range 0.05–50 μg/L. Microcystins could be detected below the 0.04 μg/L level in drinking and surface water using only 5-mL sample volumes, with UV detection. The very small sample volume, resulting from lower detection limits, in absolute amounts, obtained in micro-LC represents a definite advantage over on-line classical chromatography. The suitability of on-line micro-SPE–micro-LC–MS was also evaluated. Application to the determination of microcystins in environmental and drinking water samples are presented.