吸附管采样-气相色谱法测定空气和废气中9种卤乙酸

Determination of 9 Haloacetic Acids in Air and Exhaust Gas by Adsorption Tube Sampling Gas Chromatography

采用硅胶填料吸附管吸收采集空气或废气中9种卤乙酸,经解吸后采用气相色谱法同时测定其含量。在吸附管的前段和末段分别填入硅胶200,100mg,将吸附管与大气采样器连接,在采气流量为0.5L·min^-1的条件下,采集样品40min。将吸附管两端的硅胶分别移入具塞试管中,分别先后两次用水超声解吸,每次用水5mL,解吸5min。将解吸液移入于已盛有水30mL的分液漏斗中,加入硫酸2mL使溶液的酸度小于pH0.5,确保卤乙酸均以分子形式存在,随即加入NaCl8g并使其迅速溶解。加入4.00mg·L^-1的1,2,3-三氯丙烷内标物溶液4mL,萃取3min。分层后取上层醚液3mL,置于分液漏斗中,加入新配制的硫酸-甲醇(2+8)溶液3mL,密封,于50℃磁力搅拌条件下酯化2h,冷却,先后用250g·L^-1NaCl溶液7mL和饱和NaHCO3溶液1mL各洗涤1次。分层后取上层醚液,按仪器工作条件进行测定。结果表明:9种卤乙酸(包括一氯乙酸、二氯乙酸、三氯乙酸、一溴乙酸、二溴乙酸、三溴乙酸、一溴一氯乙酸、一溴二氯乙酸和一氯二溴乙酸)的质量浓度在0.001~2.0mg·m^-3内与相应卤代酸甲酯与内标物的峰面积之比值呈线性关系。在方法的测定条件下测得9种卤乙酸的检出限(3S/N)在0.20~1.0μg·m^-3之间。分别进行精密度和回收试验,测得回收率在91.6%~116%之间,测定值的相对标准偏差(n=6)在4.3%~7.9%之间。

Nine halogen acetic acids in air or waste gas were collected with an adsorption tube packed with silica gel, desorbed with water and then determined simultaneously by gas chromatography. At the front and the end of the adsorption tube, 200 mg and 100 mg of silica gel were packed separately and the tube was connected with the air-sampler to collect the halogen acetic acids at an air flow-rate of 0.5 L·min^-1 for 40 min. The silica gel with the adsorbed acids were transferred to 2 test tubes separately and each of the silica gel was desorbed ultrasonically twice in succession with 5 mL of water and for 5 min in each desorption. The two desorption solutions were transferred to a separatory funnel in which 30 mL of water were added previously. 2 mL of H2SO4 acid were added to make the acidity of the solution less than pH 0.5, thus to keep the analytes in their forms of acid molecules. After adding 8 g of NaCl, 4 mL of internal standard solution (containing 4.00 mg· L^-1 of 1,2,3-trichloropropane which was used as internal standard) were added and extracted for 3 min. After staying and phase-separation, 3 mL of the upper etheric phase were taken and placed in a separatory funnel, 3 mL of a freshly prepared H2SO4-CH3OH (2 + 8) solution were added, and esterification was performed at 50℃ for 2 h under tightly sealed condition with constant magnetic stirring. After cooling, wash the reaction mixture successively with 7 mL of 250 g·L^-1 NaCl solution and 1 mL of sat'd NaHCO3 solution. The upper etheric solution was taken for GC analysis as described in the instrumental-working condition. It was shown that linear relationships were found between mass concentrations of the 9 halogen acetic acids (i.e., monochloro acetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, dibromoacetic acid, tribromoacetic acid, monobromomonochloroacetic acid, monobromodichloroacetic acid and monochlorodibromoacetic acid) in the same range of 0. 001-2. 0 mg·m^-3 and the ratios of peak areas of the respective methyl halide to the internal standard. Detection limits (3S/N) for the 9 compounds were found in the range of 0.2 -1.0μg·m^-3. Tests for recovery and precision were made separatly, giving values of recovery in the range of 91.6%-116% and of RSDs (n = 6) in the range of 4.3%-7.9%.