吹扫捕集-气相色谱-质谱法测定环境空气和废气中的三甲胺

Determination of Trimethylamine in Ambient Air and Exhaust Gas by Purge and Trap-Gas Chromatography-Mass Spectrometry

建立了吹扫捕集-气相色谱-质谱法(P&T-GC-MS)测定环境空气、废气中的三甲胺含量的方法。用装有草酸浸泡过的玻璃微珠的采样管以0.5L·min-1的流量采集气体样品10L,气体样品中的三甲胺与草酸反应生成三甲胺盐,附着于玻璃微珠表面,将玻璃微珠转移至吹扫瓶内,加入氢氧化钾3.0g和水5mL,解吸出三甲胺气体,在优化的吹扫捕集条件下经捕集阱捕集解吸后进入气相色谱-质谱中分析。色谱柱选用rtx-624色谱柱,在分流进样和程序升温模式下进行色谱分离;选择电子轰击(EI)离子源,在选择离子(m/z 58,59,42)扫描(SIM)模式下进行质谱检测。结果显示:三甲胺的质量与其对应的色谱峰面积在0.05~2.00μg内呈线性关系,当采样体积为10L时,仪器检出限(3S/N)和方法检出限(3.143s)分别为1.0,1.2μg·m^-3。对3个浓度水平的以氮气为底气的三甲胺标准气体进行分析,得到的回收率为92.0%~112%,相对标准偏差(n=6)为9.4%~26%。采用本方法分析了污水处理厂废气处理塔采集的3个时段的废气和环境空气,结果显示,废气中三甲胺的排放量最高为0.017kg·h^-1,低于GB 14554-1993规定的15m排气筒高度下的三甲胺排放量限值(0.54kg·h^-1);环境空气中的三甲胺为3.2μg·m^-3,未超过GB 14554-1993规定的厂界无组织排放限值(0.05~0.80mg·m^-3)。

Purge and Trap-gas chromatography-mass spectrometry(P&T-GC-MS)was established to determine the content of trimethylamine in ambient air and exhaust gas.A sampling tube containing glass beads treated with oxalic acid was used to collect 10L of gas sample at a flow-rate of 0.5L·min^-1.The trimethylamine in the gas sample reacted with oxalic acid to form trimethylamine salt attached to the surface of the glass beads.The glass beads were transferred to the purge bottle,and 3.0g of potassium hydroxide and 5mL of water were added to promote to desorb the trimethylamine gas,which was trapped and desorbed under optimized P&T conditions and subsequently analyzed by GC-MS.rtx-624column was selected for chromatographic separation with split sampling and programmed temperature mode;In MS analysis,EI ion source and SIM mode(m/z 58,59,42)were adopted.As shown by results,the mass of trimethylamine and its corresponding chromatographic peak area showed a linear relationship within 0.05-2.00μg,and the instrument detection limit(3S/N)and method detection limit(3.143s)were 1.0,1.2μg·m^-3 at the sampling volume of 10Lrespectively.A spiked test was made by addition of trimethylamine standard solutions to nitrogen at 3concentration levels,giving recoveries in the range of 92.0%-112%,and RSDs(n=6)found were ranged from 9.4%to 26%.The proposed method was used to analyze the exhaust gas in three periods collected at the exhaust gas treatment tower and the ambient air at the sewage treatment plant boundary,and the results showed that the highest value of trimethylamine emission of exhaust gas was 0.017kg·h^-1,lower than the limit of trimethylamine emission(0.54kg·h^-1)for 15meters exhaust cylinder described in GB 14554-1993;and value of the trimethylamine in the ambient air was 3.2μg·m^-3,less than the limit of unorganized emissions of the plant boundary(0.05-0.80mg·m^-3)specified in GB 14554-1993.