What is a gas chromatograph? This is a chromatographic instrument using gas as mobile phase. The method uses the different partition coefficients of gas phase and fixed liquid phase of each component in the sample. The evaporated sample is carried to the tower through the carrier gas, and the component is repeated several times between the two phases. Dispersion, due to the different adsorption and solubility of each component, the movement speed of each component in the chromatographic column is also different. When the column grows to a certain length, they separate from each other, leave the column in turn and enter the detector. When the ion current signal is amplified, the chromatographic peaks of the components are recorded. There is much more we need to know about GC. Next, we will introduce you to the method of using gas chromatography. Let's see!

By gas chromatography

Turn on the power switch of nitrogen, hydrogen and air generator (or the main valve of nitrogen bottle), and adjust the output pressure to be stable at about 0.4MPa (the gas generator is generally adjusted at the factory without adjustment).

Turn on the gas phase switch of the chromatograph gas purifier to the on position. When the carrier gas of the chromatographic column is observed, the pre column pressure rise of B stabilizes for about 5 minutes, and turn on the power switch of the chromatograph.

Set the temperature of each working part. The conditions for thermogravimetric control analysis are set as follows: (a) furnace: initial furnace temperature 50 ℃, start time 10 minutes, heating rate 5 ℃ / min, heating rate 250 ℃ / min, end time 10 minutes; (b) Syringe and detector: both 250 ℃. Chromatographic conditions for determination of fatty acids: (a) box: the initial temperature of the box is 140 ° C, 5 minutes, 4 ° C / min, 4 ° C / min, and the termination temperature is 240 ° C, 15 minutes; (b) The detector temperature is 260 ° C, 280 ° C.

Ignition: when the detector temperature rises above 150 ° C, press the "display, shift, detector" button to detect hydrogen, and open the air on-off valve to the "on" state. The hydrogen and air pressure gauges on the chromatograph are stable at about 0.1MPa and 0.15Mpa respectively. Press the ignition switch (ignition time shall not exceed 6 ~ 8 seconds). At the same time, the bright metal sheet is close to the detector outlet. When the fire is turned on, the metal sheet will have obvious steam. If hydrogen cannot be ignited within 6 ~ 8 seconds, please release the ignition switch and ignite again. When water is found to condense in the white PTFE cover at the detector outlet, unscrew the detector cover during ignition operation to take out the water. Method for determining whether the hydrogen flame on the chromatographic workstation is ignited: observe that the baseline voltage after ignition of the hydrogen flame shall be greater than that before ignition.

Open the computer and workbench (analytical fatty acid, analytical iodine, analytical iodine), and open the method file: fatty acid analysis method or iodine analysis method. There should be a blue text in the lower left corner of the display to show the current voltage value and time. You can turn the "coarse tuning" knob on the ignition button on the chromatograph amplifier panel to check whether the signal is a path (when you turn the coarse tuning knob, the baseline should change). When the reference is stable, input the sample, and then click the "start" button or click the shortcut key next to the chromatograph to analyze the chromatographic data. When the analysis is finished, click the stop button, and the data will be saved automatically.

Shut down procedure: first shut down the hydrogen and gas source to put out the fire of the hydrogen flame detector. After the hydrogen flame is extinguished, the initial furnace temperature, detector temperature and injector temperature are set to room temperature (20-30 ° C). When the temperature drops to the set temperature, turn off the power supply of the chromatograph. Finally turn off nitrogen.