Use of a presolvent to include volatile organic analytes in the application range of on-line solid-phase extraction-gas chromatography-mass spectrometry.

The application range of the on-line solid-phase extraction-gas chromatographic (SPE-GC) analysis of aqueous samples has been extended to volatile analytes. In the new set-up, after conventional aqueous-sample loading and drying of the SPE cartridge with nitrogen gas, 30-50 μl of an organic solvent, the so-called presolvent, such as methyl acetate or ethyl acetate are introduced into the retention gap prior to the actual desorption to ensure that a solvent film is already present in the retention gap when the introduction of the analyte-containing desorption solvent starts. This procedure allows the recovery of analytes as volatile as monochlorobenzene and xylene. Aspects such as the type of retaining precolumn, and the type and amount of presolvent have been studied systematically to explain the performance of the novel set-up. Actually, when using 50 μl of presolvent, the use of a retaining precolumn did not have any significant influence on the recovery of the volatile analytes. The modified SPE-GC procedure was tested by analysing 10 ml of fiver Rhine water spiked at the 0.5 μg/l level with about 80 microcontaminants covering a wide range of volatility. The test compounds included chlorobenzenes, substituted and nonsubstituted aromatic compounds, anilines and phenolic compounds and organonitrogen and organophosphorus pesticides. The system performance in terms of recovery (typically 70-115% at the 0.5 μg/l level) and repeatability (R.S.D. values typically 1-9%; n=7) was satisfactory, even for monochlorobenzene, the most volatile analyte of the test mixture. Low recoveries due to early breakthrough (polar analytes) or adsorption to the tubing (apolar analytes) were observed for a few analytes only. The detection limits in SPE-GC-MS using full-scan acquisition generally were 20-50 ng/l