| Chlorofluorocarbons were got wild spread concern for a long time owing to their environment effect. From 1970s, their research value applying to underground water and ocean water was found and developed. Therefore, we have to establish reliable monitoring system and analysis method which can help to determine chlorofluorocarbons in the air and in water. The way of purge and trap device for enriching the chlorofluorocarbons, and gas chromatography (GC) - electron capture detector (ECD) for analyzing the CFCs were widely adopted presently. However, ECD is unsuitable for shipborne because of its radioactive source. As a exclusive detector for halogen, without radioactive source, Electrolytic conductivity detector has remarkable advantage for water sample of complex composition.According to current research results, we independently developed a P&T-GC-ELCD detection system for analyzing the chlorofluorocarbons, which was applied to detect chlorofluorocarbons in the air and water. The main studies and results in the paper are outlined as follows:1. According to the principle and procedure of purge and trap, a new-style purge and trap system was developed. For the first time, TENAX material was adopted in this system to enrich chlorofluorocarbons. The trap for CFCs at low temperature can be carried out by semiconductor refrigeration, and the trap tube could be heated up from -20℃to 160℃in 3 minutes by electron heating device. We also designed a purge tube whose volume can be regulated, from 100 mL to 600 mL. In the process of design, the effect of all materials to chlorofluorocarbons was well considered. Ultimately, stainless steel tube and Teflon tube were used as connecting line. The overall design of this system was rational and easy to handle. If programming, it can be automate.2. The result about standard gas CFC-11, CFC-12 and background value of the P&T-GC-ELCD system were as follows: the relative standard deviation of CFC-11 and CFC-12 were less than 5 %, the limit of detection were respectively 2.96×10-12 (V/V),3.68×10-12 (V/V), which primarily verify the reliability and accuracy of the whole system. TENAX trap can achieve the effective capture of standard gas CFC-12 as the trap temperature was less than -15℃, the range of flow rate of purge was from 0 to 180 mL/min, purge time, 0 ~10 min. Longer purge time and lower trap temperature(<-20℃) should be available when applied these conditions for analyzing real samples.3. Comparing result of the dehydration capability of anhydrous calcium chloride and 3A molecular sieve showed that 3A molecular sieve could strongly adsorb CFC-11 and CFC-12, and anhydrous calcium chloride had excellent dehydration capability without adsorbing CFCs, which can substitute common CFCs dehydration, such as magnesium perchlorate. The anhydrous calcium chloride could be regenerated after 40 ~ 50 water sample analysis.4. After refitting the P&T-GC-ELCD system a little, the system was applied to the concentration of chlorofluorocarbons in the air around Qingdao from February to May. the detection result of air background value and other urban observation result showed that the system refitted can continuously and accurately determine CFCs in the air; The concentration of CFCs in the air could be affected by weather and season; the concentration in the city were more than background value. The concentrations of CFCs in the air were generally in downward trend, but still there were strong emission source of CFCs in urban.5. The concentration CFCs in underground water were determined by the P&T-GC-ELCD system under optimized conditions. CFC-11, CFC-12, CHCl3, CCl4 could be separated effectively, the limit of detection was 0.03 ~ 0.14 pmol/L, the relative standard deviation was 2.11 % ~ 6.14 %, the recovery was 92.6 % ~ 104.7 %. The results testified that the P&T-GC-ELCD system designed could apply to the detection of CFCs in water. |
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