USE OF A PRESOLVENT TO INCLUDE VOLATILE ORGANIC ANALYTES IN THE APPLICATION RANGE OF ONLINE SOLID-PHASE EXTRACTION GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

The application range of the on-line solid-phase extraction-gas chroma tographic (SPE-GC) analysis of aqueous samples has been extended to vo latile analytes. In the new set-up, after conventional aqueous-sample loading and drying of the SPE cartridge with nitrogen gas, 30-50 mu l of an organic solvent, the so-called presolvent, such as methyl acetat e 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 des orption 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 be en studied systematically to explain the performance of the novel set- up. Actually, when using 50 mu l of presolvent, the use of a retaining precolumn did not have any significant influence on the recovery of t he volatile analytes. The modified SPE-GC procedure was tested by anal ysing 10 mi of river Rhine water spiked at the 0.5 mu g/l level with a bout 80 microcontaminants covering a wide range of volatility. The tes t compounds included chlorobenzenes, substituted and nonsubstituted ar omatic compounds, anilines and phenolic compounds and organonitrogen a nd organophosphorus pesticides. The system performance in terms of rec overy (typically 70-115% at the 0.5 mu g/l level) and repeatability (R .S.D. values typically 1-9%; n=7) was satisfactory, even for monochlor obenzene, the most volatile analyte of the test mixture. Low recoverie s due to early breakthrough (polar analytes) or adsorption to the tubi ng (apolar analytes) were observed for a few analytes only. The detect ion limits in SPE-GC-MS using full-scan acquisition generally were 20- 50 ng/l. (C) 1998 Elsevier Science B.V. All rights reserved.