Benzene and benzene series detection method Secondary thermal desorption gas chromatography
1. Principle Benzene and benzene series in the air are collected by activated carbon tube, then adsorbed to Tenax-TA tube after thermal desorption, and then thermally desorbed, and analyzed by gas chromatography to determine the retention time and peak height.
2. equipment
2.1 Activated carbon tube (containing 0.1g (coconut shell) activated carbon) and Tenax-TA tube (containing 0.1g Tenax-TA);
2.2 Atmospheric sampler;
2.3 10uL micro syringe;
2.4 Secondary thermal desorption apparatus;
2.5 GC9160 gas chromatograph (containing 50m long, 0.53mm inner diameter, capillary column coated with dimethyl polysiloxane, liquid film thickness
3.00μm, hydrogen flame ionization FID detector, external chromatography workstation).
3. Pharmaceutical reagents benzene or benzene series (containing benzene, toluene, ethylbenzene, para (m) xylene, o-xylene, a total of 5 substances) standard sample series (BR (benzene / benzene series) concentration C (mg / mL ) See instructions).
4. sampling
4.1 Use an activated carbon tube activated according to 5.5.1, connect it with an atmospheric sampler, generally collect 10L of gas at a flow rate of 0.5L / min, and record the temperature (t, ℃) and air pressure (p, kPa) of the sampling point, Calculate the sampling volume V0 in the standard state according to 6.2. For details, please refer to Operation Guide ADT / OG011-B.0-2007 "Requirements for Atmospheric Sampling and Acceptance of Indoor Environmental Pollutants".
4.2 The sample after sampling shall be stored in a dry dish at room temperature, and the measurement shall be completed according to 5.4.1 ~ 5.4.5 within 5 days.
5. Steps
5.1 Flow setting.
5.2 Temperature setting.
5.3 Drawing of standard curve
5.3.1 Open the standard sample series of benzene or benzene series, and clean the 10uL micro syringe with blank solvent.
5.3.2 Turn the six-way valve to 1 (if not in position), and install the activated carbon tube activated according to 5.5.1 at the calibration port (hereinafter referred to as "sampling tube 1").
5.3.3 Install the 0.1g Tenax-TA tube (hereinafter referred to as "sampling tube 2") activated according to 5.5.2 (if not installed) at the 2nd place of thermal desorption.
5.3.4 Use a 10uL micro syringe to accurately measure 1uL 4 # benzene or benzene series standard samples (bubble should be cleaned up).
5.3.5 At the injection port 1, slowly insert the syringe into the injection gasket and quickly inject 1µL of 1uL 4 # benzene or benzene series standard sample, at which time the timing starts.
5.3.6 When the needle stays for 1 minute, pull out the syringe quickly.
5.3.7 After another 4 minutes (that is, a total of 5 minutes), remove the sampling tube 1 at the calibration port and install thermal desorption 1.
5.3.8 After putting a cold trap at 2 places of thermal desorption, put a thermal desorption furnace at 1 place of thermal desorption, and turn on the "Carrier Gas 2 Switch" knob (if not opened), the six-way valve turns to 2, Time starts counting.
5.3.9 After 4 minutes (the sampling tube 1 is basically cold adsorbed to the sampling tube 2 after thermal analysis), turn off the "carrier gas 2 switch" knob (plug the "carrier gas 2 empty" with your fingers, if the "carrier gas 2 is adjusted" "The pointer does not move, you can be sure that the carrier gas 2 is off).
5.3.10 Remove the cold traps at two places of thermal desorption, and put on the thermal desorption furnace.
5.3.11 After 1 minute, turn the ten-way valve to 1 and press the button of the chromatographic workstation (A or B in the channel with the signal) (if it is a benzene series, press the "start" button of the gas chromatograph at the same time) .
5.3.12 After all the corresponding component peaks have been output, please refer to the operation instructions for details, remove the thermal desorption furnace at 2 thermal desorption points and 1 thermal desorption point, turn the six-way valve to 1, and the ten-way valve to 2. And turn on the "Carrier Gas 2 Switch" knob.
5.3.13 After saving the spectrum, after the temperature of the sampling tube 1 and gas chromatography is completed, remove the sampling tube 1 at the thermal desorption 1 and repeat 5.3.1 ~ 5.3.13, respectively, 1uL 3 #, 2 #, 1 # Benzene or benzene series standard sample injection, determine the peak height Hm / nm of each standard sample (if it is benzene series n = 1,2, ... 5) (m = 1,2,3,4), For details, please refer to "Determination Method of Concentration of Indoor Environmental Pollutants Benzene Series".
5.3.14 The common logarithm of the mass of each component of benzene or benzene series lgMm / nm (μg) (if it is benzene series n = 1,2, ... 5) (m = 1,2,3,4) is The abscissa Xn, the common logarithm of peak height lgHm / nm is the ordinate Yn, calculate the standard curve regression equation according to 6.1, draw the standard curve, and obtain the regression line slope Kn (peak height common logarithm / μg), and take 1 / Kn (Common logarithm of peak height / μg) is used as the calculation factor BM / nM (μg / common logarithm) of each group of samples.
5.3.15 Take 1uL 2 # benzene or benzene series standard sample in a 10uL micro-syringe and measure the peak height Hm / nm of the sample tube after operation according to 5.4.1 and 5.3.2 ~ 5.3.13, according to the following formula CC6H6 / n measurement (mg / mL) = 10 (lgHm / nm-B6H6 / n) × BM / nM / 1 (if benzene series n = 1 is benzene, 2 is toluene, 3 is ethylbenzene, 4 is para ) Xylene, 5 is o-xylene) Calculate the standard sample measurement concentration CC6H6 / n measurement, if the relative error τ (| CC6H6 / n measurement -CC6H6 / n | / CC6H6 / n) does not exceed 5%, then use this standard Curve, otherwise repeat 5.3.1 ~ 5.3.15.
5.4 Determination of each component of the sample
5.4.1 Turn off the carrier gas 2. Determine the peak height H0 / n0 of the baseline blank according to 5.3.11 and 5.3.12 (if the baseline is above 10mV, repeat 5.4.1).
5.4.2 Install sampling tube 1 at thermal desorption 1 and operate according to 5.3.3 and 5.3.8 ~ 5.3.13. The peak height of the sample tube is H1 / n1 (if it is benzene series n = 1,2, ... 5) (according to the sample number from small to large).
5.4.3 Calculate the concentration C1 / n1 (mg / m3) of each component of the sample according to 6.3 (if it is benzene series n = 1,2, ... 5).
5.4.4 Repeat 5.4.1 ~ 5.4.4 for the next sample measurement (if necessary).
5.4.5 Activate the capillary column and sampling tube 2 according to 5.5.3 and 5.5.2 respectively.
5.5 Various activations
(Applicable to activated carbon tubes that do not sample more than 5 days, Tenax-TA tubes that do not sample more than 14 days, and capillary columns that do not sample more than 7 days.)
5.5.1 Activated carbon tube: basically activated once, the activated carbon tube is stored in a drying dish (it can be sampled when the baseline is stable below 10mV, and can be reused 30 times.
5.5.2 Tenax-TA tube: 0.1g basic activation 1
This article is derived from the detection method of benzene and benzene series. Secondary thermal desorption gas chromatography | Scientific instrument online original link: http: //
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