Analytical method development for the determination of four biocides used in antifouling paints in estuarine waters and sediments by gas chromatography-mass spectrometry

Irgarol 1051, chlorothalonil, dichlofluanid and diuron are biocides utilised in antifouling paints as alternatives to organotin compounds, after restrictions imposed in the use of tributyltin in 1987. Effective analytical methods for the simultaneous determination of these four biocides in waters and sediments have been developed and method performance data are presented. Quantification is by gas chromatography - electron ionisation mass spectrometry (GC-EI-MS). The method involves the simultaneous extraction of the biocides from water with dichloromethane or from sediments with dichloromethane and acetone. For the determination of diuron the extract was methylated prior to GC analysis to avoid thermal degradation in the instrument. The method was applied to water and sediment samples spiked with the biocides. The highest detection sensitivities were achieved in the selected-ion monitoring (SIM) mode. Recovery studies were performed at 20, 2 and 1 ppb for all biocides in water and 400, 40 and 20 ppb in sediments. The percentage recoveries ranged between 90 and 100 % for waters and 80 and 90 % for sediments. Seven determinations were made at each concentration level along with a procedural blank. The quantification limit of the method was around 0.2 ppb for water and 5 ppb for sediments depending on the individual compound.