Application of headspace solid-phase microextraction and gas chromatography coupled with in-situ derivatisation to the determination of phenols in water

Headspace solid-phase micro-extraction technique utilising various fibre coatings has been applied to the determination of phenolic compounds in water samples using gas chromatography with flame-ionisation detection. Phenols were converted into their acetyl derivatives applying in-situ derivatisation. It was observed that normalised responses of the detector in the case of mixed-coating fibres: 65 mu m PDMS-DVB (polydimethylsiloxane with divinylbenzene polymer) and 65 mu m CW-DVB (Carbowax with divinylbenzene polymer) were higher than those of 85 mu m PA (polyacrylate) and 100 mu m PDMS - coated fibres. Normalised responses of the detector changed in the following order: PDMS-DVB > CW-DVB > PA > PDMS and for all investigated compounds strongly increased after addition of an inorganic salt (NaCl, KCl or Na2SO4). For the most frequently used sodium chloride, responses increased by about one order of magnitude. The strongest increase was observed for anhydrous sodium sulphate: 1.3-3.7-fold increase compared to that observed for sodium chloride. Linear range of response was obtained over a wide range of phenols' concentration in water samples for polyacrylate-coated fibre. For this reason, PA fibre is preferably used when flame-ionisation detection is applied. In contrast, for PDMS-DVB fibre, non-linear dependence of the detector response on the concentration of the analysed species was observed. This was caused by the adsorptive-absorptive properties of the coating. However, only PDMS-DVB fibre allowed one to achieve very low detection limit.