Abstract: Gas chromatograph is a new general separation analysis technology with high separation efficiency, high selectivity, high sensitivity, fast analysis speed, accurate qualitative and quantitative, wide application range, and small sample consumption.
The gas chromatograph has a wide range of applications in the analysis of air and waste gas such as CO2, CH4 and some trace pollutants. Many components in the landfill gas generated by the landfill, such as CO2, CH4, and some VOCS, can be adjusted and selected for optimal operating conditions.
Such as: choice of carrier gas flow rate, choice of carrier gas, choice of column temperature, choice of column shape and column length for separation and analysis. Gas chromatography is widely used in the analysis of landfill gas.
Landfill gas is generally monitored by gas chromatography.
The main gases of landfill gas are CH4 and CO2. According to foreign data, in a typical landfill, the content of CH4 can reach 45% ~ 50%, while the content of CO2 can reach 40% ~ 60%. In China, due to the high content of food waste, the water content is also Be high abroad. Therefore, the content of CH4 in landfill gas in China is higher than that in foreign countries. Studies have shown that the content of CH4 in landfill gas in Shenzhen is 62.2%, while the content of CO2 is 34.7%. The main gas of the landfill gas must be monitored.
There is no national standard for the monitoring and analysis methods of CH4 and CO2. Currently, foreign countries mainly use portable gas analyzers for analysis. But it can also be analyzed by gas chromatography.
1. Instruments and equipment gas chromatograph, equipped with thermal conductivity cell detector, chromatography data workstation, high purity nitrogen, 100 ml medical syringe.
2. Gas chromatographic analysis conditions One glass-filled column, column length 2m, column internal diameter 3mm, internal loading 40 ~ 60 mesh GDX-502, carrier gas is high-purity nitrogen, column flow rate 60ml / min, column temperature 30 ℃, gasification The chamber temperature is 120 ° C, the detector temperature is 120 ° C, the cell current is 50mA, and the injection volume is 0.5ml.
Under these conditions, the measured gas composition is characterized by retention time and quantified by the external standard peak height method. Since both gases are inert, no obvious adsorption or desorption occurs between them and the glass injector of the sampler. The collected gas samples can be kept for a long time, and the sample concentration changes little, which has no significant effect on the measurement results. In addition, because this method uses a syringe to directly sample from the scene, the short sampling time has the advantage of instantaneous sampling, which is suitable for the measurement of gas generation. This method does not need to add any gas adsorbent during the sampling process, and there is no problem of adsorption recovery rate, so the accuracy is very high.
Gas chromatographic monitoring of landfill gas trace gas includes many trace gases in the landfill gas. Although the concentration of these trace gases is very low, they are highly toxic and pose great harm to the environment and human health. Most trace gases are volatile organic pollutants (VOCS). In some developed countries such as the United States, some trace aromatic compounds and halogenated compounds have been used as routine monitoring items for landfill air. Zou Shichun and others in China have detected up to 63 VOCS by monitoring the second landfill in Guangzhou, 16 of which are priority pollutants controlled by the US Environmental Protection Agency (USEPA), including benzene, toluene and ethylbenzene , Vinyl chloride, chloroform, chlorobenzene and other pollutants [7]. This indicates that there are toxic organic substances that can produce three-way effects in the air of the landfill, and the landfill may become a serious source of pollution.
1. Gas Chromatography Monitoring of Benzene Series 1.1 Principle Activate carbon adsorption sampling tube to enrich benzene, toluene, ethylbenzene, xylene, etc. in the air, add carbon disulfide for desorption, separate by DNP Bentane column, flame ionization Detected by the detector, qualitative by retention time, quantified by external standard method of peak height.
1.2 Instruments and equipment Gas chromatograph: with flame ionization detector, chromatographic column length 2m, inner diameter 3mm stainless steel column, filled with Chromosorb W HP DMCS (80 ~ 100 mesh) coated with 2.5% DNP and 2.5% Bentan ; Air sampler: flow rate 0 ~ 1L / min; activated carbon adsorption sampling tube.
1.3 Chromatographic conditions Column temperature: 64 ℃; gasification chamber temperature: 150 ℃; detector temperature: 150 ℃.
Carrier gas nitrogen flow rate: 50ml / min; fuel gas hydrogen flow rate: 46ml / min; auxiliary gas flow rate: 320ml / min. Under these conditions, experimental measurements were performed. Prepare the standard stock solution of benzene series first, then inject and measure, and draw the standard curve.
2. Determination of non-methane hydrocarbons by gas chromatography 2.1 Main equipment and reagents (1) Gas chromatograph, hydrogen flame ion detector (FID); (2) TD-1 thermal desorption instrument; (3) activated carbon Adsorption sampling tube, length 10cm, inner diameter 6mm, wall thickness 0.8 ~ 1mm; (4) syringe, 1ul, 5ml, 100ml; (5) atmospheric sampler, sampling flow rate 0 ~ 1L / min; (6) n-hexane standard solution.
2.2 Chromatographic analysis conditions Silanized glass microspheres (60-80 mesh) stainless steel packed column: column length 3m, injector temperature 170 ℃, detector temperature 170 ℃, auxiliary temperature 160 ℃, column temperature 75 ℃, carrier gas Flow rate (N2) 30VmL / min, gas flow rate (H2) 30Ml / min, auxiliary gas flow rate (O2) 300ml / min; injection volume: direct injection 1Ml.
2.3 The preparation of n-hexane standard gas uses N2 as the blank dilution gas. Pipette 1uL of n-hexane standard solution into a 100ml N2 syringe filled with N2. After complete volatilization, shake well. The gas in this syringe is the standard source gas. Then draw 1ml of standard source gas into another syringe with nitrogen gas and shake it. This gas is the standard gas for qualitative and quantitative analysis.
Determination of aldehydes and ketones by gas chromatography
1. Reagents and standard samples of formaldehyde, acetaldehyde, acrolein, butyraldehyde, and benzaldehyde are of analytical grade, n-valeraldehyde is of superior grade, and acetone, butanone, and acetophenone are of analytical grade. 2,4-Dinitrophenylhydrazine, AR; carbon disulfide, AR, now steamed; double-distilled water is steamed before use. 2,4-Dinitrophenylhydrazine absorption solution: dissolve the appropriate amount of 2,4-dinitrophenylhydrazine solid with 1mol·l-1 sulfuric acid to make a saturated solution, and extract twice with 1/10 (V / V) carbon disulfide . The absorption solution should be prepared and purified within 48h before sampling.
2. Apparatus and its conditions The gas chromatograph and chromatographic column are SE-54 capillary columns with a length of 25m and an internal diameter of 0.32㎜; the detector is an electron capture detector. Constant temperature of column temperature 220 ℃; gasification temperature 270 ℃; detector temperature 375 ℃; carrier gas N2, 40ml · min-1, split ratio 1:50. Inflow 1μl.
3. Experimental method Two U-shaped porous glass plate absorption tubes were used to collect air samples in series, and the absorption tube was filled with 10ml of 2,4-dinitrophenylhydrazine absorption solution. The sampling device is an air sampler, and the rotameter is calibrated with a soap film flowmeter. The sampling speed is 0.5 ～ 1.0 ml · min -1, and the sampling time is 10 ～ 60 min. After the sample is collected, it is quantitatively transferred to a 100 ml separating funnel and extracted with 2 × 5ml CS2. Transfer the organic layer to a 25 ml volumetric flask and make up to 25 ml with CS2. Qualitative by relative retention time, quantified by external standard method.
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