Silicone Rubber Sorptive Stir Bar: Preparation And Its Application In Analysis Of PAHs In Aqueous Samples

Solid-phase microextraction (SPME) is a solventless sample pretreatment technique that makes extraction, concentration, desorption and injection to be done in one step. Because of this simpleness, high efficiency, friendliness to environment, SPME has been widely used to couple with gas chromatography (GC) or liquid chromatography (LC) for trace analysis. Based on SPME technique, stir bar sorptive extraction (SBSE) has been developed, which possess an extraction phase about 50-250 times larger than that of conventional SPME resulting in largely increased enrichment factors. Moreover, the stir bar can finish extraction during stirring samples. So SBSE technique is suitable for extraction of trace amount of organic compounds in food and environmental sample.In this work, a novel thick silicone rubber coating stir bar was prepared for sorptive microextraction. The silicone rubber stationary phase was made by a sol-gel-sulfurization method from methyl-vinyl and vinyl-terminated silicone rubbers. Proportion of the ingredients used in sol solution was optimized by single factor and orthogonal test method. The processing of silicone rubber sulfurization and the aging were also investigated. The silicone rubber coating shows homogeneous and porous appearance checked by SEM. Using multi-stage sulfurization and three aging steps at different temperature gruaranteed no peeling and cracking to the coating. The coating can withstand desorption temprature up to 280℃. The life span of the stir bar was about 150 times. The reproducibility in the preparation of stir bars was also studied by checking the performance in the same batch or different batches.Coupled with homemade Thermal Desorption System (TDS) and GC, the method of SBSE-TDS-GC (FID) was established by the analysis of 6 PAHs in water. The factors influencing extraction efficiency, such as extraction time, ion strength, extraction temperature, pH value and stirring speed were discussed. Desorption temperature, time and times were studied too. The linear range of the method was 0.3-103μg/L, the limits of detection (LODs) were 0.002 -0.011μg/L, and the relative standard deviations (RSD) were 0.92 %-6.14 %. This method can meet the demand of USEPA (the DL and RSD of the EPA507 method were 2.8 -14 ng/L and (RSD) <30 %, respectively.)The extraction efficiencies of different style stir bars, 1cm (3mg, 6mg), 2cm (3mg) and 3cm (6mg, 13mg), were checked in optimized conditions except extraction time varied from 5 min to 30 min. It was found the RSDs were less than 12.4 %, the LODs were in the range of 2-140 ng/L. The results indicates, 1cm (3mg, 6mg) and 2cm (3mg) bars can be used for micro analysis, 3cm (6mg, 13mg) bars can be used for trace analysis. Rain water was analyzed under optimum conditions, the PAHs, recoveries of standard addition were 79.2%-101%.