Determination of Toxic Air Substances in Workplaces Using Gas Chromatography

　　This standard is formulated to implement the "Industrial Enterprise Design Hygiene Standard" and "Occupational Exposure Limits for Hazardous Factors in the Workplace". This standard is a monitoring method supporting the occupational exposure limits for harmful factors in the workplace, and is used to monitor the concentration of heterocyclic compounds (including pyridine, furan and tetrahydrofuran, etc.) in the air of the workplace. This standard is proposed after summarizing, generalizing and improving the original standard method.

　　Determination of toxic substances in workplace air Heterocyclic compounds 1 Scope This standard specifies the method for monitoring the concentration of heterocyclic compounds in workplace air.

　　This standard applies to the determination of heterocyclic compound concentrations in workplace air.

　　2 Normative references The clauses in the following documents become the clauses of this standard through reference in this standard. For all referenced documents with dates, all subsequent amendments (excluding errata) or revisions are not applicable to this standard. However, parties that reach an agreement based on this standard are encouraged to study whether the latest versions of these documents can be used. For all referenced documents without dates, the latest versions are applicable to this standard.

　　GBZ159 Sampling Specifications for Monitoring Hazardous Substances in Workplace Air 3 Solvent Desorption of Tetrahydrofuran and Pyridine - Gas Chromatography 3.1 Principle Tetrahydrofuran in the air is collected using a 401 organic carrier tube, and pyridine is collected using an activated carbon tube. After solvent desorption, the samples are injected, separated by a chromatographic column, and detected by a hydrogen flame ionization detector. The retention time is used for qualitative analysis, and the peak height or peak area is used for quantitative analysis.

　　3.2 Instrument 3.2.1 401 organic support tube, solvent desorption type, containing 150 mg/75 mg 401 organic support.

　　3.2.2 Activated carbon tube, solvent desorption type, containing 100mg/50mg alkaline activated carbon.

　　3.2.3 Air sampler, flow rate 0~500ml/min.

　　3.2.4Solvent desorption bottle, 5ml.

　　3.2.5 Micro syringe, 10ml.

　　3.2.6GC-5890 series gas chromatograph , hydrogen flame ionization detector.

　　Automatic sampling and injection system can be selected, and automatic online analysis can also be performed. Please call us for instructions when ordering: Ms. Li 18974821899 GC-5890 Gas Chromatograph Technical Parameters 1. Temperature Control Temperature Control Range: 7℃~400℃ above room temperature (increment 0.1℃)

　　Ramp-up steps: three-step Ramp-up rate: 0.1℃~50℃/min (increment 0.1℃)

　　2. Detector FID detection limit: ≤5×10-12g/s (n-hexadecane)

　　Baseline noise: ≤6×10-12A/H Linear range: ≥105 Stable time: <20min3. TCD sensitivity of detector: ≥10000mV? ml/mg (n-hexadecane)

　　Baseline noise: ≤30uV (carrier gas is 99.999 hydrogen)

　　Gas chromatograph instrument operating conditions: chromatographic column: 2m×4mm, FFAP:ChromosorbWAWDMCS=10:100; column temperature: 100oC; vaporization chamber temperature: 160oC; detection chamber temperature: 160oC; carrier gas (nitrogen) flow rate: 45ml/min.

　　3.3 The water used in the reagent experiment is distilled water.

　　3.3.1401 Organic support, 20-40 mesh: first soak and shake with ether, filter out the ether to remove the organic matter adsorbed on the support, then wash with methanol to remove the residual ether, then wash out the methanol with distilled water, dry at 120℃ for 2h, and seal for later use.

　　3.3.2 Alkaline activated carbon, 20-40 mesh: soak in 6 mol/L hydrochloric acid solution for 30 min, wash with water until neutral, boil in 50 g/L sodium hydroxide solution for 10 min, dry at 140 °C, and seal for later use.

　　3.3.3 Desorption liquid: carbon disulfide (for tetrahydrofuran desorption), dichloromethane (for pyridine desorption), chromatographic identification without interfering peaks.

　　3.3.4FFAP, chromatographic stationary phase.

　　3.3.5ChromosorbWAWDMCS, 60~80 mesh.

　　3.3.6 Standard solution: Add about 5 ml of desorption solution to a 10 ml volumetric flask, weigh accurately, add a certain amount of tetrahydrofuran or pyridine, weigh accurately again, and dilute to the scale with desorption solution; calculate the solution concentration from the difference between the two weighings, which is the standard stock solution. Before use, dilute with desorption solution to a 1.0 mg/ml standard solution. Or prepare with a nationally recognized standard solution. [page]

　　3.4 Collection, transportation and storage of samples On-site sampling shall be carried out in accordance with GBZ159.

　　3.4.1 Short-time sampling: At the sampling point, open both ends of the solid adsorbent tube and collect air samples for 15 minutes at a flow rate of 100 ml/min.

　　3.4.2 Long-term sampling: At the sampling point, open both ends of the solid adsorbent tube and collect air samples for 2 to 8 hours at a flow rate of 50 ml/min.

　　3.4.3 Individual sampling: At the sampling point, open both ends of the solid adsorbent tube and wear it on the upper chest of the sampling subject, with the air inlet facing upwards and as close to the breathing zone as possible, and collect air samples for 2 to 8 hours at a flow rate of 50 ml/min.

　　After sampling, immediately seal both ends of the solid adsorbent tube and place it in a clean container for transportation and storage. Tetrahydrofuran can be stored in a refrigerator for 7 days. Pyridine can be stored at room temperature for 7 days.

　　3.5 Analysis steps 3.5.1 Control test: Bring the solid adsorbent tube to the sampling point. Except for not connecting the sampler to collect air samples, the rest of the operations are the same as the sample, which serves as a blank control for the sample.

　　3.5.2 Sample processing: Pour the sampled front and rear adsorbents into the solvent desorption bottle, add 1.0 ml of desorption liquid, seal, shake for 1 min, desorb for 30 min, and use the desorption liquid for determination. If the concentration of the analyte in the sample desorption liquid exceeds the determination range, it can be diluted with the desorption liquid and then determined, and the dilution factor should be multiplied when calculating.

　　3.5.3 Drawing of standard curve: Dilute the standard solution with desorption liquid to 0.0, 10.0, 25.0, 50.0, 100 and 250 mg/ml tetrahydrofuran standard series, 0, 10, 20 and 40 μg/ml pyridine standard series. Refer to the instrument operating conditions, adjust the gas chromatograph to the optimal measurement state, inject 2.0 ml respectively, and measure each standard series. Repeat the measurement 3 times for each concentration. Draw a standard curve with the measured peak height or peak area average against the tetrahydrofuran or pyridine concentration (mg/ml).

　　3.5.4 Sample determination: Determine the desorbed solution of the sample and blank control using the operating conditions of the standard series; subtract the peak height or peak area of ​​the blank control from the measured sample peak height or peak area, and obtain the concentration of tetrahydrofuran or pyridine (mg/ml) from the standard curve.

　　3.6 Calculation 3.6.1 Convert the sampling volume into the standard sampling volume according to formula (1): 293PVo=V×-----×-----……(1)

　　273 t101.3 Where: Vo - standard sampling volume, L; V - sampling volume, L; t - air temperature at the sampling point, ℃; P - atmospheric pressure at the sampling point, kPa.

　　3.6.2 Calculate the concentration of tetrahydrofuran or pyridine in the air according to formula (2).

　　(c1 c2) vC=―――――――……(2)

　　VoD: C is the concentration of tetrahydrofuran or pyridine in the air, mg/m3; c1, c2 are the measured concentrations of tetrahydrofuran or pyridine in the desorption liquid before and after, mg/ml; v is the volume of the desorption liquid, ml; Vo is the standard sampling volume, L; D is the desorption efficiency, %.

　　3.6.3 The time-weighted average allowable concentration shall be calculated in accordance with the provisions of GBZ159.

　　3.7 Description 3.7.1 The detection limit of this method is 5.1 mg/ml for tetrahydrofuran and 0.5 mg/ml for pyridine. The minimum detection concentration is 3.4 mg/m3 for tetrahydrofuran and 0.3 mg/m3 for pyridine (based on the collection of 1.5L air sample). The measurement range is 5.1~250 mg/ml for tetrahydrofuran and 0.5~40 mg/ml for pyridine. The relative standard deviation is 2.5%~5.9% for pyridine.

　　3.7.2 The penetration capacity of 100 mg of adsorbent is: 2.64 mg for tetrahydrofuran and 21 mg for pyridine. The average sampling efficiency is 100%; the average desorption efficiency is 82.5%. The desorption efficiency of each batch of solid adsorbent tubes should be measured.

　　3.7.3 Toluene, chlorobenzene, furfural and furan that may coexist in the on-site air do not interfere with the determination of tetrahydrofuran; p-dichlorobenzene does not interfere with the determination of pyridine.

　　3.7.4 This method can use corresponding capillary chromatographic columns.