Instrument: GC-7890 gas chromatograph
Thermal desorption instrument: ATDS-3420 online thermal desorption instrument
Adsorption tube: Tenax TA desorption temperature: 300 ℃
Detector: FID Temperature: 200 ℃
Chromatography column: detection of benzene derivatives using a modified PEG-20M stainless steel packed column with a diameter of 3 × 2M;
Detection of TVOC using a 50M × 0.53 TVOC specific capillary column
Carrier gas: high-purity nitrogen flow rate: 30ml/min
Column temperature: 90 ℃; The initial temperature is maintained at 50 ℃ for 10 minutes, and the temperature is raised to 250 ℃ at a rate of 5 ℃/min.
1. The thermal desorption/capillary gas chromatography method specified in the existing standard method does not specify the sampling temperature in the on-site application of Tenax adsorption tubes. The sampling flow rate is set at 0.5L/min, and the sampling time is 20 minutes. Experimental results have shown that sampling temperature, sampling flow rate, and sampling time have a significant impact on the components and adsorption rates (or adsorption penetration rates) of benzene and TVOC. Through experiments, the recommended optimal sampling conditions are: adsorption tube sampling temperature: 5 ℃± 3 ℃; Sampling flow rate: 100-250ml/min;; Sampling time: 10 minutes. Under the recommended optimal conditions above, it can be ensured that the adsorption thermal desorption recovery rate of all TVOC components, including benzene, can reach over 90%. It should be noted that the recovery rate of benzene can reach around 97%.
2. Under the condition of not using a thermal decomposition sampler and adsorption tube cold trap sampling, 20L of coconut shell activated carbon adsorption tube can be used for the determination of benzene in the air. CS2 can be used for extraction, and 1 μ L of the extraction solution can be directly injected. The chromatographic column can be a capillary column or a packed column. Through experiments, it is recommended to use a large-diameter capillary column SE30 30m × 0.53mm × 1-3 μ m or 50m × 0.53mm × 3 μ m. Compared with packed columns, its advantages are high detection sensitivity, high separation efficiency, high analysis accuracy, and long column service life. The key points to note when using activated carbon with attached tubes and CS2 extraction method are: CS2 must undergo careful purification treatment; Benzene derivatives in activated carbon are not easily activated and should be deducted from blank values; The sensitivity requirement for instrument FID detection is high, and the detection limit D should be ≤ 5 × 10-12g/s to meet the lower limit requirement of the method detection.
3. By using Tenax TA adsorption tube cold trap to sample 1-2.5L, and directly injecting it into the capillary column system with a thermal desorption sampler, accurate analysis data of benzene and TVOC can be obtained simultaneously with one sampling and one injection, saving analysis time, improving work efficiency, and avoiding the problem of using a large amount of high-purity CS2 when measuring benzene.