Optimisation and comparison of several microextraction/methylation methods for determining haloacetic acids in water using gas chromatography

Abstract

This article presents the different modes and configurations of liquid-phase microextraction (LPME) through comparison with headspace solid-phase microextraction (HS-SPME) for the simultaneous extraction/ methylation of the nine haloacetic acids (HAAs) found in water. This is the first analytical case reported of solvent bar extraction–preconcentration–derivatisation assisted by an ion-pairing transfer for HAAs. In this method, 5 μL of the organic extractant, decane, was confined within a hollowfibre membrane that was placed in a stirred aqueous sample containing the derivatising reagents (dimethylsulphate with a tetrabutylammonium salt). With heating at 45 °C in the HS-SPME method, some organic solvents (extractant, excess of derivatising reagent) are also volatilised and compete with the esters on the fibre (the fibre is damaged and it can be reused only 50−60 times). In addition, the HSSPME method provides inadequate sensitivity (limits of detections between 0.3 and 5 μg/L) to quantify HAAs at the level usually found in drinking waters. Alternative headspace LPME methods for HAAs require heating (45 °C, 25 min) to derivatise and volatilise the esters but, by using solvent bar microextraction (SBME), the extraction/methylation takes place at room temperature without degradation of HAAs to trihalomethanes. Adequate precision (relative standard deviation of approximately 8%), linearity (0.1–500 μg/L) and sensitivity (10 times higher than the HSSPME alternative) indicate that the SBME method can be a candidate for routine determination of HAAs in tap water. Finally, the SBME method was applied for the analysis of HAAs in tap and swimming pool water and the results were compared with those of a previous validated headspace gas chromatography–mass spectrometry method.