Styrene in the air is adsorbed in the activated carbon tube. The sample is injected after thermal desorption. After separation by polyethylene glycol 6000 column, it is detected by ammonia flame ionization detector. The retention time is qualitative and the peak height is quantitative.
Activated carbon tube: a 150 mm long glass tube with an inner diameter of 3.5-4.0 mm and an outer diameter of about 6 mm is used to load 100 mg of 20-40 mesh coconut shell activated carbon. Both ends are fixed with a small amount of glass wool. This tube can be used in a short time. It can also be sealed in a 250mm long glass tube with the same inner diameter, which can be used for long-term preservation. The activated carbon should be treated with nitrogen at 300 ~ 350 ℃ for 3 ~ 4H before pipe installation. It can also be used for short-term application or storage by blowing nitrogen at the above temperature for 5-10min without treatment before tube installation.
Sampling pump: 0 ~ 1L / min.
Syringe: 100ml, 1ml,
Microinjector: 10pl, 1pl
Thermal desorption instrument ： Domestic thermal desorption It 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, FID detector, 5 ng styrene gave a signal-to-noise ratio of at least 31
Chromatographic column: column length 2m, inner diameter 4mm, stainless steel column.
Polyethylene glycol 6000:6201 support = 5:100
Column temperature: 90 ℃
Temperature of vaporizer: 150 ℃
Detection room temperature: 120 ℃.
Carrier gas (nitrogen): 69ml / min.
Open the activated carbon tube at the sampling site, with the aperture of at least 2mm at both ends, and extract 1L air at 0.2l/min. After sampling, put plastic caps on both ends of the tube and take it back to the laboratory for analysis as soon as possible.
Control test: with the same sampling, the carbon tube was brought to the site, but no air was extracted, and the sample analysis was taken as the blank control.
Sample treatment: connect the sample tube with a 100ml syringe, place it on the thermal desorption device, and use nitrogen to desorb at the speed of 50ml / min at 300 ~ 350 ℃. The desorption volume was 100 ml.
Drawing of standard curve: a certain amount of styrene was accurately measured with a micro syringe (the mass of 1 PL styrene was 0.9063 mg at 20 ℃) and injected into a 100 ml syringe to prepare a certain concentration of standard gas. Take a certain amount of styrene standard gas and dilute it with air to 0.02, 0.05, 0.1, 0.2, 0.4 pg / ml styrene standard gas. Take 1 ml of sample respectively, and measure the retention time and peak height
Repeat three times for each concentration, take the average value of peak height, plot the peak height with the content of styrene, draw the standard curve, and take the retention time as the qualitative index.
Sample analysis: take the thermal desorption gas sample, inject 1ml, qualitative by retention time and quantitative by peak height. The chromatogram of styrene is shown in the figure below.
The suitable temperature of thermal desorption of styrene is 300 ~ 350 ℃. Under the experimental conditions, the average desorption efficiency is 80.1%, 86.4%, 89.4% when the concentration of styrene is 20, 40, 400 mg / M ~ 3. Due to the low desorption efficiency, the desorption efficiency is used to correct the calculation results.