| 英文摘要 |
NIEA A722.71B, widely used for the analysis of the gaseous organic compounds from the stacks, was modified in 1999 to include new QA/QC procedures as part of the method. Considering the complicated VOC characteristics and varying moisture contents in the exhaust gas, it is necessary to estimate the interference, the variation of accuracy and the preservative period for the VOCs samples. Consequently, this study was undertaken to collect the relevant information from 10 certified environmental laboratories and 2 research institutes.
The results show that a better calibration is feasible when the concentration below 500 ppm. Because of the insufficient vaporized temperature for the more liquid standard in the water bath, the residual percentages for some aromatics (styrene, m-xylene and o-xylene) was 2.5-3.0% under the higher concentration conditions (>500ppm). As for Tedlar bag, the twice cleaning frequency of the new Tedlar bag with the zero air of 80% bag’s volume should be sufficient. The residual percentages of 17 VOCs was only 0.3%-0.9% for the samples with higher concentration (300-500ppm) after 18 times cleaning at 60-80℃. However, the bag for mobile tail gas samples is difficult to clean since more than 10% residuals remaining for some VOCs after 54 times cleaning at 60℃. For this reason, it is suggested that the Tedlar bag not be reused after sampling higher VOC concentrations (>200ppm) of the exhaust gas.
The influence of moisture content in the Tedlar bag on the decrease of VOCs is significant. The trends of VOC decay during the storage period are similar for humidity up to 10%, but they are different at higher humidity (25%). The data for Tedlar bag storing at higher temperatures (25℃ or 35℃) are better than the results at 15℃. In addition, the QA/QC results for acetone, methyl ethyl ketone and methyl acetate conform to the norm in their calibration, accuracies and precisions.
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