在线大气汞分析仪渗透管标定方法研究

Calibration methods for an on-line atmospheric mercury analyzer using a permeation tube

为了实现在线大气汞分析仪的自动标定,本文选用商用的汞渗透管,自主设计了渗透恒温装置（控温精度为0.1℃）,搭建了大气汞分析仪的标定模块,利用该模块建立了3种标定方法.与本实验组研发的在线大气汞分析仪联用对3种方法进行对比研究.①稀释气法：与经典的渗透管动态配气法相同,通过改变稀释气体流量（1~5 L,精度为20 mL）实现发生不同浓度的标准气（0~99 n.gm-3）,所建立的工作曲线线性良好（R2=0.9968）.②固定浓度时间调控法：发生一个固定浓度的汞标准气,通过改变采样时间使富集量不同进而建立工作曲线（R2=0.9968）;③补气法：去掉稀释气路,渗透管载气流量保持不变,补给零空气以达到分析仪的采样流量,改变采样时间实现汞的梯度富集（R2=0.9972）.方法2和3主要适用于富集效率不受样品浓度影响的预富集型汞分析仪的标定.3种标定方法所得结果吻合较好（回归直线的总体斜率无差异）.稀释气法与环境大气的实际情况最接近,通过改变采样时间调控富集量的方法标定用时较短.该标定模块成本低,稳定性好,操作简易.

In order to calibrate an on-line atmospheric mercury analyzer automatically,a calibration module including three calibration methods was realized using the commercial Dynacal permeation device for which a thermostat（precision of temperature control was 0.1℃）was designed.The on-line atmospheric mercury analyzer developed by a PKU group was used to test the calibration methods.①Dynamic volumetric method：the same as the conventional permeation tube method,mercury with different concentrations（1~99 ng·m-3）was generated by changing the flow rates of the diluent gas（1~5 L,precision is 20 mL）.A good linearity of the working curve（R2=0.9968）was achieved.②Time adjustment with a fixed concentration：the concentration of generating mercury could be comparatively fixed,and different sampling times were set to achieve different enrichment amounts,then the standard curve was established（R2=0.9968）.③Time adjustment with zero-air supply：zero air could be supplied to achieve the sample volume without diluents while gas flow of the permeation tube was held constant.The concentration gradient was achieved by changing sample time（R2=0.9972）.Method 1 is suitable for all atmospheric mercury analyzers.Methods 2 and 3 could also be used if the analyzer has a pre-enrichment function and different concentrations do not affect enrichment efficiency.The results of the three calibration methods were in agreement（the overall slope of the regression line had no significant difference）.Calibration by generating different concentration mercury vapor was most equivalent to ambient environment,while methods through time adjustment were faster.In general,the low cost calibration module was stable and convenient to operate.