GB/T 33646-2017Determination of the ester compounds in motor rasoline—Gas chromatography (English PDF)

8.1 Gas chromatographic conditions

If different instruments are used, then the optimal analysis conditions may be different; thus, it is impossible to give the general parameters for the gas chromatographic analysis. The setting parameters shall ensure the to-be-tested components to be separated and tested effectively. The parameters given in Appendix A are proven to be feasible.

8.2 Sample injection

Directly take about 1.5mL of sample and place it into 2.0mL sample flask (6.6); manually or take autosampler to inject 1.0µL specimen into gas chromatograph (6.1); perform the chromatographic analysis according to the optimized method conditions.

If the content of ester compounds in the sample exceeds the test range specified in Clause 1, the sample shall be suitably diluted (for instance, isooctane - xylene solution with volume ratio of 5:1).

8.3 Qualitative analysis

Test the standard working solution (5.5) and specimen under the same instrument analysis conditions; perform the qualitative analysis according to the retention time of ester compounds chromatographic peak. The reference retention time of 3 kinds of ester compounds can refer to Appendix B.

A.1 Establishment of valve blowback column system

A.1.1 Adjust the valve to the positive blow position (1 in Figure A.1); adjust the flowrate to control Valve A, so that the flowrate can reach the setting value in Table A.1. Measure the flowrate on the detector exit sample side.

A.1.2 Adjust the valve to the blowback position (2 in Figure A.1); measure the flowrate on the detector exit sample side. If compared with flowrate in Table A.1, the flowrate changes; adjust the flowrate control valve B, so that the flowrate is changed within ±1mL/min.

A.1.3 Switch the valve from the positive blow position to the blowback position for several times; observe the baseline; The change in pressure caused by initially switching of the valve shall not generate the change or drift of the baseline. If baseline changes, slightly adjust the flow control valve B, so that the baseline is stable.

A.2 Determination of blowback time

Prepare the n-nonane solution containing n-octane with volume ratio of 5%. Under the positive blow state, inject 1µL of such solution into the system. Record the chromatogram until the n-nonane flows out, the recorder pen returns to the baseline.

Measure the time from the sample injection to the recorder pen returns to the baseline between the n-octane and n-nonane peak, in seconds. At this point, the n-octane has flowed out, while the n-nonane has not. Half of such measurement time can be approximated as "blowback time", and shall be slightly adjusted within 30s~60s.

Repeat the above operation including the sample injection, switch to blowback state according to the above determined "blowback time". Then obtain the n-octane chromatogram, while the n-nonane peak is very small or invisible in the chromatogram.

If necessary, do the further test, adjust "blowback time" till all n-octane peaks appear; there is very small or no n-nonane peak. The "blowback time" obtained through actual valve operation is required to be used in all the following calibration and analysis.

A.3 Instrument conditional parameters

When using different instruments, the optimum analysis conditions may be different; so it is impossible to give the general parameters for gas chromatographic analysis. […]