AN IMPROVED APPROACH FOR ONLINE SOLID-PHASE EXTRACTION GAS-CHROMATOGRAPHY

An improved setup for interfacing solid-phase extraction (SPE) and gas chromatography (GC) was constructed. Its working mechanism resembles that of the loop-type interface, but due to the use of small desorptio n volumes (50-100 mu L) in combination with a long 0.53 mm i.d. retent ion gap, the application range also includes volatile analytes. The in terface is equipped with a 6-port and a 14-port valve. The 6-port valv e is used to divert the carrier gas either to the GC system or to the 14-port valve, on which a liquid chromatography (LC) precolumn and two loops for storing organic solvent are mounted. After loading the samp le on the LC precolumn and drying by nitrogen purging, both valves are switched simultaneously. The solvent in the first loop effects phase swelling of the retaining precolumn in the GC system, which increases the application range at the volatile end. The solvent in the second l oop desorbs the analytes from the stationary phase in the LC precolumn and transfers them to the GC system. The on-line SPE-GC approach was tested by analyzing a mixture of pesticides in 10-mL water samples usi ng mass selective detection. System performance in terms of recovery, repeatability, linearity, and robustness was satisfactory. The detecti on limits in the full-scan mode generally were 0.1 mu g/L or better. W ith postrun ion extraction, the detection limits were in the 2-20 ng/L range. For the purpose of target analysis, SPE-GC-mass spectroscopy u sing selected ion monitoring (SIM) was applied to the analysis of seve ral classes of compounds, including chlorophenols, chloroanilines, and nitromusk compounds. The detection limits in the SIM mode were down t o 0.2 ng/L. The procedure was extended to the analysis of diluted sedi ment extracts in which several microcontaminants were detected and ide ntified. (C) 1996 John Wiley & Sons, Inc.