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

KeyWord:aqueous sample  volatile siloxanes  HS-SPME  GC-MS

Abstract:

      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 ¦ÌL of 500 ¦Ìg/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 ¡æ 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 ¡æ£¬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 ¦Ìg/L£¬respectively.