Chloroethylene in air was collected by activated carbon tube, and then injected after thermal desorption. The sample was separated by dinonyl phthalate column and detected by flame ionization detector. The retention time was qualitative and the peak height was quantified.
Activated carbon tube: a 250mm long glass tube with an inner diameter of 3.5-4.0mm and an outer diameter of about 6mm is used to put 100mg of 20-40 mesh coconut shell activated carbon, and both ends are fixed with a small amount of glass wool. The activated carbon should be treated with nitrogen at 300 ~ 350 ℃ for 3 ~ 4H before pipe installation. After the pipe is installed, the pipe is blown with nitrogen at the same temperature for 2 ~ 3 min. It can not be treated before pipe installation. After pipe installation, nitrogen is used to blow at the above temperature for 5 ~ 10min. In short time, both ends should be covered with plastic caps for preservation, while in a long time, both ends should be sealed with fire.
Sampling pump, 0 ~ 1L / min.
Syringe, 100ml, 1ml
Domestic thermal desorption The thermal desorption unit is mainly composed of heater, temperature controller, thermometer and gas flow controller. The temperature control range is 100 ~ 350 ℃, the desorption gas is nitrogen, and the flow control range is 50 ~ 100ml / min. The structure of the thermal desorption device used should be such that the activated carbon tube can be easily inserted into the heater, and the gas passing through the pipe is preheated first, and the activated carbon is heated evenly.
Gas chromatograph: flame ionization detector. The SNR of 0.4 ng vinyl chloride is not less than 31.
Chromatographic column: column length 2m, inner diameter 4mm, stainless steel column. Dinonyl phthalate: 6201 support = 10:100;
Column temperature: 90 ℃ (60 ℃ for vinyl chloride measurement alone);
Temperature of vaporizer: room temperature;
Detection room temperature: 150 ℃
Carrier gas (nitrogen): 40ml / min.
Open the activated carbon tube at the sampling site, with the aperture of at least 2mm at both ends, place it vertically, and extract 1L air at the speed of 0.05 ~ 0.2l/min. After sampling, put plastic caps on both ends of the tube for analysis as soon as possible.
Take the activated carbon tube to the site and bring it back to the laboratory along with the sample for analysis as blank control.
The air inlet of the sample tube is connected with a 100ml syringe, and placed on the thermal desorption device. The desorption volume is 100ml with nitrogen at the speed of 50 ~ 60ml / min at 200 ℃.
Standard curve drawing
Use a 1ml syringe to take a certain volume of pure vinyl chloride gas (under standard conditions, the mass of 1ml vinyl chloride gas is 2.79mg), and inject it into a 100ml syringe to prepare a certain concentration of standard gas. Take a certain amount of vinyl chloride standard gas, dilute to 0.015, 0.03, 0.15, 0.3jg/ml of vinyl chloride standard gas, take 1ml of sample, measure the retention time and peak height, repeat three times for each concentration, and take the average of peak height
The standard curve was drawn by plotting the peak height with the content of vinyl chloride. Retention time is a qualitative indicator.
Take 1ml desorbed gas for injection, qualitative analysis with retention time and quantitative analysis by peak height. The chromatogram is shown in the figure below.
In the application of thermal desorption method, the desorption efficiency of the tested organic compounds at the desorption temperature should be tested first, and it can be used when the desorption is nearly complete. If the desorption efficiency is a little low, but the result is still stable, it should be corrected when using standard gas to calculate the result quantitatively.
In order to check whether the activated carbon tubes are contaminated, generally, the first batch of samples should be analyzed with 2 ~ 3 blank tubes. The blank tubes should be brought to the site together with the sampling tubes, and then brought back from the site as blank analysis.