Jiedao IslandGC1690Sulfur hexafluoride（SF6）Introduction to Gas Chromatography:

Product name: Gas chromatograph

Model: Sulfur Hexafluoride（SF6）Gas chromatograph

Manufacturer: Jiedao

Sulfur hexafluoride（SF6）As a tracer gas, it is widely used in ventilation field pressure prevention and fire extinguishing technology to detect air leakage channels, air leakage volume, and determine the location of fire sources in goaf or fire areas. Tracer gasSF6The analysis mainly utilizes chromatography and selects an electron capture detector（ECD）The chromatograph has been used to complete the measurement, and we have chosen1690EPerform testing using a gas chromatograph. Basic principle: An electron capture detector is a selective and highly sensitive detector that only produces signals for components with electronegativity (referring to the probability of molecules or atoms capturing electrons to generate negative ions). It is suitable for analyzing substances containing halogen molecules and substances containingO、S、N、PThe sensitivity of atomic substances increases with the enhancement of their electronegativity, making them widely used in the analysis of polyhalogenated and polysulfide compounds.

1、 Jiedao IslandGC1690Sulfur hexafluoride（SF6）Experimental conditions for gas chromatography:

1Instrument:GC1690Gas chromatography detector (includingECDDetector)
2Sample gas for testing:SF6Standard gas499ppm(Shanghai)
3Carrier gas: high-purityN2（99.999%）
4Chromatography Workstation（N2000）

2、 Jiedao IslandGC1690Sulfur hexafluoride（SF6）Experimental steps of gas chromatograph

1Preparation of standard gas
SF6Standard gasSF6Standard gas sampling volume Volume after constant volume with air
499ppm 0.1mL 100mL
4.99ppm 1mL 100mL
Accurately extract a certain amount of high concentration according to the table aboveSF6Standard gas is injected separately into the air filled system100mLIn the syringe, Formulated to the required concentrationSF6And mix evenly.
2Instrument conditions
Chromatographic column:5AMolecular sieve column φ3mm×0.5mm×1m；
Column temperature:30-40℃； Vaporization chamber temperature:100℃；
Detector temperature:100℃； Sensitivity: High
Carrier gas: Nitrogen（99.999%）
Current Speed:20-40mL/minInjection volume:0.1mL
2.1 Column selection for chromatography
Due to the fact that electron capture detectors only generate signals for substances with the ability to capture electrons,SF6It is the substance with the strongest electronegativity. In actual samples, only oxygen in the air has strong electronegativity, which affectsSF6The direct measurement is therefore selected5AZui is an ideal because5Amolecular sieve adsorptionO2Compared to adsorption abilitySF6Strong ability, that is to say, in the gas sampleO2andSF6After passing through the chromatographic column, components with weak adsorption capacitySF6First, flow out of the chromatographic column, andO2Then flow out of the chromatographic column afterwards, thus avoiding largeO2Peak masking low concentrationSF6Peaks facilitate qualitative and quantitative analysis, improving analytical sensitivity.
2.2 Selection of carrier gas flow rate
The magnitude and stability of the carrier gas flow rate have a significant impact on the analysis, The flow rate range is usually selected within20~40mL/minButECDAs a concentration type detector, its detected response value is proportional to the concentration of the substance in the carrier gas and is not affected by changes in the carrier gas flow rate. However, it affects its retention time. When the flow rate is fast, the retention time is short. Due to the temperature of the column box we are currently using30℃, so at higher room temperatures,30℃ may not be controllable, it is necessary to increase the column temperature to40-50At ℃, the flow rate can be adjusted to slow down and maintain good separation.
2.3 analysis result
equalSF6When the concentration is high,SF6The generated signal is very strong and will mask itO2The peak, therefore499ppmofSF6In the chromatogram peak of the standard gasSF6Feng JiangO2Covering a part, it seems like it hasn't been separated yet.

The repeatability of peak height and peak area is shown in the following table:

The repeatability of peak height and peak area is shown in the following table:

From the above analysis results, it can be concluded that the accuracy of the analysis is high, and the repeatability is1%The analysis results have high reliability.
2.4 According to the calculation, the maximum detectable concentration is:5.0×10-11That is50ppt.

3、 Jiedao IslandGC1690Sulfur hexafluoride（SF6）Discussion and Technical Parameters of Gas Chromatography Results:

3.1 Chromatographic operating conditions:5AMolecular sieve, column length1m, inner diameter φ2mmAttenuation:1Carrier gas: high-purity nitrogen; Current Speed:40mL/minInjection volume:0.1ml
3.2 By calculation, our instrument isSF6The minimum detectable concentration has reached5.0×10-11It meets the needs of coal mine applications.

Instrument configuration

Instrument:GC1690EGas chromatograph (includingECDDetector)

Sample gas for testing:SF6Standard gas499ppm(Shanghai)

Carrier gas: high-purityN2（99.999%）

Chromatography workstation（N2000）