Determination of Six Volatile Siloxanes in Aqueous Samples by HS-SPME/GC-MS

A headspace solid-phase microextraction(HS-SPME) coupled with gas chromatography-mass spectrometric(GC-MS) method was developed for the analysis of four cyclic(D3,D4,D5 and D6) and two linear volatile methyl siloxanes(L3 and L4) in aqueous samples.Parameters affecting the performance of HS-SPME/GC-MS,including fiber coating,desorption time,pH value,extraction temperature,extraction time and salinity,were studied.The optimum conditions were as the follows:40 mL of water sample was placed in a 60 mL headspace vial containing a magnetic stir bar.40 μL of 500 μg/L internal standard(M4Q) and 0.1 g/mL NaCl were added into vial,and then the vial was tightly sealed with a Teflon septum.HS-SPME with PDMS/DVB fiber was carried out at 24 ℃ for 45 min.After the extraction,the fiber was removed from the vial,and inserted into the injection port of GC-MS system for thermal desorption(200 ℃,2 min) and analysis.The method detected limits(LOD) of six target compounds ranged from 2.6 ng/L to 7.8 ng/L.Their recoveries ranged from 82% to 96% with relative standard deviations(RSDs,n=5) of 1.1%-7.9%.The results indicated that the method was simple,rapid,sensitive,and was suitable for the determination of volatile methyl siloxanes in aqueous samples.With the optimized method,the six target compounds were measured in 24 aqueous samples collected from Qinghe WWTP and Qinghe River.L4,D3,D4,D5 and D6 were detectable with concentrations of 0.07-0.21,0.07-0.59,0.05-4.30,0.02-7.60,0.04-7.13 μg/L,respectively.