Drying agents for water-free introduction of desorption solvent into a GC after on-line SPE of aqueous samples

During the on-line solid phase extraction-gas chromatographic (SPE-GC) analysis of water samples it was necessary to avoid the introduction of traces of water into the GC. Thus, a small cartridge containing a drying agent was inserted between an SPE column and the GC column to enable the introduction of water-free desorption solvent into the GC. Six drying agents (the anhydrous sulphates of sodium, magnesium, calcium and copper, silica and molecular sieve) had the appropriate characteristics, namely they were both reusable and chemically inert. Possible interactions of the drying agent with analytes, namely irreversible adsorption or catalysed degradation, were checked for a wide range of alkanes, alkylbenzenes, chlorobenzenes, chlorophenols and phthalate esters. The repeatability of the method was satisfactory (6-17 per cent) using the on-line SPE-GC system with flame ionization detection (FID) and spiked samples containing different levels of the test compounds. For 10 ml samples, the detection limits were lower than 0.1 ug per litre. The on-line SPE-GC-FID system was used for repeated analysis of tap water samples without exchange of the drying cartridge.