Determination of methane,propane,butane or isobutane by direct injection gas chromatography in the air of workplace
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Objective To establish a direct injection gas chromatography method for the determination of methane,propane, butane or isobutane in the air of workplace.Methods Methane,propane,butane or isobutane in the air of workplace were collected by a syringe or a air bag with direct injection,and then analyzed by GC.Results The method showed a good linearity with the correlation coefficient(r0.999) and the relative standard deviation 1.2%～1.6%(n = 6 ).The limit of quantification of the method was 0.50 mg/m~3.When air bag was used for sampling,methane and propane can be stored at room temperature for at least 8 days,and isobutane or butane for at least 5 or 2 days.Contrarily,when sampling with a syringe,the samples should be measured on the same day as soon as possible.Conclusion The established new method could be used for determination of methane,propane,butane or isobutane in the air of workplace.Keywords:
Isobutane
Propane
Butane
Flame ionization detector
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Abstract An analytical procedure is described for the determination of dissolved oxygen and methane in groundwater samples. The method consists of generating a helium gas headspace in a water filled bottle, and analysis of the headspace by gas chromatography. Other permanent gases such as nitrogen, and volatile aliphatic hydrocarbons such as ethane, propane, and butane could also be analyzed. BTX analyses could also be done on the sample. Detection limit for oxygen was 0.1 mg/l and 0.002 mg/l for methane. Good agreement was shown between Winkler titration and the GC-Headspace Equilibration Technique for oxygen analyses by a linear regression coefficient, R 2 = 0.998. Oxygen was greatly depleted in some field samples when they were stored for 30 days at 4°C without hydrochloric acid preservation.
Hydrochloric acid
Propane
Butane
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Low-density polyethylene
Propane
High-density polyethylene
Degradation
Propene
Butane
Hexane
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Using glass syringe(gas bag) collection of samples,which directly determined samples by gas chromatography equipped with a hydrogen flame ionization detector and double columns.Injection of 1.0 mL sample into the vaporizer,respectively in total hydrocarbon column and methane column,due to the differences in the two pillars fill material and length,total hydrocarbon was produced in the FID signal first,and then the methane.Deducted from total hydrocarbon concentrations of methane and hydrocarbon oxygen,the concentrations of non methane hydrocarbon(NMHC) methane were got,and a single sample acquired the concentrations of total hydrocarbon,methane,and NMHC.The scope of 1.37 ～ 22.3 mg/m3 standard methane gas was researched,methane standard curve equation for Y = 715x + 829 and r = 0.9990 were obtained,the relative standard deviation was 0.26% ～ 1.8%,total hydrocarbon standard curve equation for Y = 695X + 724,the relative standard deviation was 0.35% ～ 1.4%,and hydrocarbon-free air(O2-N2,20.8%) relative standard deviation was 0.75%.The method was used in analysis of NMHC in ambient air and stationary sources emission,the operation was simple and the experimental results were satisfied.
Flame ionization detector
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Objective:To establish a gas chromatographic method for determination of methylal in the air of workplace.Methods: Air sample of workplace was collected by active charcoal tube,then desorbed with CS2.The eluent was detected by gas chromatography.Results: The linear range of methylal was 0.003 mg/ml~15.05 mg/ml and correlation coefficient was 0.9999.The minimum detection concentration was 0.6 mg/m3 for 1.5 L air of workplace.The quantitative detection limits were 2.9 μg/ml,2.0 mg/m3,respectively.Relative standard deviation was below 1.0%,and average desorption efficiency was 98.8%.Conclusion: The method was suitable for determination of methylal in air of workplace.
Activated Charcoal
Relative standard deviation
Charcoal
Linear range
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Objective: To establish a solvent desorption gas chromatography method for determination of cyclohexene in workplace air. Methods: Cyclohexene in the air of workplace was collected with carbon tube and desorbed by carbon disulfide. The target toxicant was separated with the GC column and analyzed with FID detector, identified by retention time, and quantified by peak area. Results: The linear range of cyclohexene in the air of workplace was 0.77~4 050.00 μg/ml, with a correlation coefficient of 0.9999. The limit of detection was 0.23 μg/ml. The lower limit of quantification was 0.77 μg/ml. The minimum detectable concentration was 0.15 mg/m(3) under1.5 L sampling volume and 1.0 ml extraction solution volume. The within-run precision of different cyclohexene concentrations was 0.62%~1.9% and the between-run precisions was 1.5%~3.5%; The average extraction efficiency was 96.4%; Penetration capacity (100 mg of carbon tube) was 29.4 mg; The average collection efficiency was 100%; The samples could be stored for 7 days at room temperature. When placed in 4 ℃ refrigerator, the samples could be stored for 14 days. The potential coexistence of cyclohexane, hexane, benzene, toluene and ethylbenzene with cyclohexene in the air did not interfere with the results of determination. Conclusion: This method has high sensitivity, precision, accuracy and lower limit of detection and it is applicable for determination of cyclohexene in workplace air.目的： 建立工作场所空气中环己烯的溶剂解吸-气相色谱测定方法。 方法： 工作场所空气中环己烯用活性炭管采集，二硫化碳解吸后，经气相色谱柱分离，氢火焰离子化检测器检测，以保留时间定性，峰面积定量。 结果： 环己烯在0.77~4 050.00 μg/ml范围内呈线性关系，相关系数为0.999 9；方法检出限为0.23 μg/ml，定量下限为0.77 μg/ml，在采样体积为1.5 L，解吸液体积为1.0 ml的条件下，方法的最低检出浓度为0.15 mg/m(3)；批内和批间精密度（RSD）分别为0.62~1.9%、1.5~3.5%；平均解吸效率为96.4%；穿透容量（100 mg活性炭吸附剂）为29.4 mg；平均采样效率为100%；样品在室温下可保存7 d，置于4 ℃冰箱内可保存14 d；空气中可能与环己烯共存的环己烷、正己烷、苯、甲苯和乙苯，在该方法条件下不干扰测定。 结论： 本方法灵敏度高，精密度好，准确度好，检出限低，适用于工作场所空气中环己烯的现场监测。.
Carbon disulfide
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Objective To establish a gas chromatography method for the determination of butadiene in the air of workplace by solvent desorption.Methods Butadiene in the air was adsorbed by active carbon tube,and dichloromethane was used for solvent desorption,then the sample was analyzed by GC(FID) with capillary column.Results The linear regression equation was y=0.898x-2.06,at the target concentration of 0.1-4.0 mg/m3 in air(r=0.999 7).The detection limit was 0.6 μg/ml.The average desorption efficiency was 93.2%.Active carbon tube sampling butadiene tightly closed could be stored for three days at 4 ℃ and the results still remained stable.Conclusion This method is simple,sensitive,accurate and applicable to the determination of butadiene in the air of workplace.
Dichloromethane
1,3-Butadiene
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Objective:To establish a method for simultaneous determination of benzene series(benzene,tolune,xylene,ethylbenzene,styrene),n-hexane and cyclohexane in air of workplace by solvent desorption-capillary gas chromatography.Methods: The sample was collected with active carbon tube,desorbed by carbon disulfide,and separated with DB-1 capillary column and detected by FID.Results: The 7 organic chemicals could be determined simultaneously,with the relative standard deviations from 3.11% to 4.02%,and the linear ranges of method were from 0.14 to 0.33 μg/ml,the correlation coefficient was more than 0.999.The desorption efficiency were all above 95% except styrene was 80.2%.Conclusion: The method is simple,accurate and suitable for simultaneous determination of the 7 target chemicals in the air of workplace
Carbon disulfide
Flame ionization detector
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Analysis of dissolved methane, ethylene, acetylene, and ethane in water is crucial in evaluating anaerobic activity and investigating the sources of hydrocarbon contamination in aquatic environments. A rapid chromatographic method based on phase equilibrium between water and its headspace is developed for these analytes. The new method requires minimal sample preparation and no special apparatus except those associated with gas chromatography. Instead of Henry's Law used in similar previous studies, partition coefficients are used for the first time to calculate concentrations of dissolved hydrocarbon gases, which considerably simplifies the calculation involved. Partition coefficients are determined to be 128, 27.9,1.28, and 96.3 at 30°C for methane, ethylene, acetylene, and ethane, respectively. It was discovered that the volume ratio of gas-to-liquid phase is critical to the accuracy of the measurements. The method performance can be readily improved by reducing the volume ratio of the two phases. Method validation shows less than 6% variation in accuracy and precision except at low levels of methane where interferences occur in ambient air. Method detection limits are determined to be in the low ng/L range for all analytes. The performance of the method is further tested using environmental samples collected from various sites in Nova Scotia.
Acetylene
Propane
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A method of thermal desorption gas chromatographic determination of difluorodichloro methane in air over workshop was proposed according to the requirements mentioned in reference.Difluorodichloro methane in air was sampled by active carbon,from which it was desorbed by the thermo-desorbing instrument,and introduced directly into the gas chromatograph.After separation on the FFAP column,the object compound was detected by the hydrogen flame ionization detector.Linear relationship was found in the range within 2 000 mg·L-1(r=0.998 7) of difluorodichloro methane.Detection limit of the method was found to be 8.5×10-2mg·L-1.Precision of the method was tested at 3 different concentration levels(500,1 000,2 000 mg·L-1) and values of RSD′s obtained were in the range of 2.0%-4.6%.Permeability capacity calculated from the experimental data was 20 mg of difluorodichloro methane for each 100 mg of active carbon.The desorption efficiency for different concentration of difluorodichloromethane were all larger than 90%.The proposed method was suitable to be used for worksite monitoring of difluorodichloro methane in air over the workshop.
Flame ionization detector
Thermal desorption
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Propylene oxide
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