Analysis of isothiazolinones in environmental waters by gas chromatography–mass spectrometry

This paper describes an analytical method for the determination of five biocides of isothiazolinone type (2-methyl-3-isothiazolinone (MI), 5-chloro-2-methyl-3-isothiazolinone (CMI), 1,2-benzisothiazolinone (BIT), 2-octyl-3-isothiazolinone (OI), 4,5-dichloro-2-octyl-3-isothiazolinone (DCOI)) in environmental waters. The method is based on pre-concentration of the analytes by solid-phase extraction onto a mixture of a polymeric material and RP-C18 material and subsequent determination by gas chromatography–mass spectrometry (GC–MS). One of the target compounds (BIT) is derivatised with diazomethane after pre-concentration to improve its chromatographic performance. The method was optimised with respect to pre-concentration conditions (liquid–liquid extraction versus solid-phase extraction, solid-phase material, elution solvent and volume) and extensively validated. Applying the method to surface waters, groundwaters, and drinking waters, limits of detection between 0.01 and 0.1 μg/l could be achieved and the repeatability was below 10% for all compounds except for MI. Additional investigations showed that the stability of the isothiazolinones in environmental waters is limited and sample storage at 4 °C is mandatory to preserve the target biocides. First investigations of influents and effluents of a wastewater treatment plant showed that conventional wastewater treatment exhibits a high efficiency for removal of the isothiazolinones. In river waters, the target isothiazolinones could not be detected.