GB/T 44238-2024Hydrogen for proton exchange membrane fuel cell vehicles - Determination of helium, argon, nitrogen and hydrocarbons - Gas chromatography (English PDF)

5.1 Gas

5.1.1 Carrier gas and fuel gas. hydrogen, with a purity of not less than 99.999%. The contents of helium, argon and nitrogen in hydrogen shall all be less than 1 µmol/mol. It is advisable to use hydrogen produced by a hydrogen generator.

5.1.2 Tail gas. nitrogen, with a purity of not less than 99.999%.

5.1.3 Combustion-supporting gas. Air, dry air that meets the requirements for use of gas chromatograph. An air generator with a purifier can be used.

5.2 Gas reference materials

5.2.1 The qualifications of the production (development) institutions of gas reference materials shall comply with the requirements of JJF 1342.Users shall give priority to the use of certified gas reference materials. The nominal value of gas reference materials shall be 3 significant figures.

5.2.2 The recommended gas reference substances shall include the following components. helium, argon, nitrogen, methane, ethane, propane, n-butane, n-pentane, n-hexane, benzene, toluene, and the balance gas is hydrogen. The preparation scheme can also be designed according to the needs.

5.2.3 It is recommended to prepare at least 2 gas reference substances with different content levels. One of them is used as a sample for routine calibration. The target value shall be the same or similar to the technical indicator limit of the corresponding component in GB/T 37244 or other purposes of hydrogen. The other content level reference substances can be used as quality control samples.

6.1 Gas chromatography system

6.1.1 Composition of gas chromatography system The system consists of a gas chromatograph equipped with a valve injection component, a split/splitless injection port, a thermal conductivity detector and a flame ionization detector. It can also be composed of two gas chromatographs equipped with a thermal conductivity detector and a flame ionization detector respectively. The typical gas chromatograph gas flow is shown in Figure A.1 in Annex A.

6.1.2 Chromatographic columns

6.1.2.1 A chromatographic column with a stationary phase of bonded polystyrene- divinylbenzene is selected as a pre-separation column to separate helium, oxygen/argon/nitrogen components from non-target components. Other equivalent chromatographic columns may also be used. A chromatographic column with a stationary phase of molecular sieve is selected as a separation column for helium, argon, oxygen, and nitrogen components. The resolution of argon and oxygen components shall be no less than

2.Other equivalent chromatographic columns may also be used.

6.1.2.2 A chromatographic column with aluminum oxide as the stationary phase is selected as the hydrocarbon component separation column. Other equivalent chromatographic columns may also be used.

6.1.2.3 Typical chromatographic columns that meet the analysis requirements of this method are shown in A.2.

6.1.3 Thermal conductivity detector (TCD) Use TCD to detect helium, argon and nitrogen components. The technical indicators of the detector shall meet the following requirements. - The dynamic linear range is greater than 104; - The sensitivity not less than 10000 mV·mL/mg.

6.1.4 Flame ionization detector (FID) Use FID to detect hydrocarbon components. The technical specifications of the detector shall meet the following requirements. - The dynamic linear range is greater than 107; - The minimum detection limit is less than

6.2 Sampling gas cylinders Sampling gas cylinders shall comply with the requirements of GB/T 44262 and GB/T 43306.

7.3 Blank analysis Use hydrogen that meets the requirements of

5.1.1 as a blank sample and test until the baseline signal is stable. The blank value signal is lower than the lower limit of determination of the target compound.

7.4 Sampling

7.4.1 General requirements The connection between the gas cylinder and the gas chromatograph inlet shall be based on the principle of small gas contact area and short connection distance. Needle valve shall be used as gas flow regulating valve. Stainless steel pipe shall be used for connecting pipeline. The injection method and injection pressure of calibration sample and sample shall be consistent.

7.4.2 Sample injection method Open the outlet valve of the sample or calibration gas cylinder. Purge the injection system including the sample loop in one of the following two ways. - Continuous purge method. During the test sequence of a specimen, keep the gas cylinder outlet valve open. Continuously purge the sampling system with a certain flow of gas. The gas flow rate shall be stabilized at a fixed value of 80 mL/min~100 mL/min. - Intermittent purge method. Purge the injection system with a stable gas flow for at least 2 min. Close the outlet valve of the gas cylinder. After 2 s~5 s, start the analysis process immediately. Introduce the gas sample in the quantitative loop into the chromatographic column. The gas flow rate shall be stabilized at a fixed value of 80 mL/min~100 mL/min. NOTE. A flow meter can be connected to the outlet of the sample purge pipeline to observe the gas flow.

7.5 Calibration sample analysis Perform 5 initial measurements on the calibration gas reference material. Continue the measurement until the difference between two consecutive measurement results meets the repeatability requirement. Take the average value as the quantitative basis. Typical chromatograms are shown in Figures A.2 and A.3.Calibration analysis shall be performed on the day of sample analysis.

7.6 Sample analysis Using the same analytical conditions as the calibration samples, perform 5 initial measurements on the sample. Continue the measurement until the difference between two consecutive measurement results meets the repeatability requirement. Take the average of these two results as the calculation data for the sample. The sample shall be tested within 7 days after collection. The storage of the sample shall refer to the provisions of GB/T 34525.

7.7 Instrument standby When no sample analysis is being performed, the column box temperature shall be set to 150°C. The instrument shall not be shut down as much as possible. Frequent switching on and off may cause the instrument to be unstable.