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1 Heating Because of the different manufacturers and quality of gas chromatographs, the way to set the temperature is different. For setting the temperature with the microcomputer setting method or the dial selection method, it is generally to directly set the number or select a suitable given temperature value to raise the temperature. If you use the knob positioning method, there are skills.
1.1 Over-temperature positioning method The temperature control knob is adjusted to a temperature lower than the operating temperature of about 30°C to increase the temperature of the gas chromatograph. When overheating to approximately the operating temperature, with the temperature indicator and heating indicator, and then gradually adjust the temperature control knob to the appropriate position.
1.2 Step-by-step incremental positioning method Turn the temperature control knob to the heating direction by an angle, the temperature rise starts, the indicator light is on; when the temperature is basically stable, turn the temperature control knob in the same direction and start to continue heating; so gradually adjust until constant temperature Working temperature.
2 adjust the pool to adjust the pool balance, in fact, adjust the balance of heat conductive bridge, so that it has a more appropriate output. Speaking of adjustment techniques, it is actually a gas chromatograph with adjustment functions such as pool balance, zero adjustment, and recording zero adjustment.
In the first step, use the pool balance or zero knob to adjust the recorder pointer to the proper position;
The second step, self-attenuation to about 16 times, observe the pointer movement of the recorder;
The third step, using the recording zero knob to turn the recorder pointer back to the original;
The fourth step, return attenuation, observe the recorder pointer movement;
In the fifth step, use the zero adjustment or the pool balance knob to return the recorder pointer to its original position.
3 Ignition of the hydrogen flame gas chromatograph requires ignition at start-up, sometimes after a flameout due to various reasons, it also requires ignition. However, we often encounter ignited conditions. Here are two kinds of ignition techniques for the peers to try.
3.1 Increase the hydrogen flow rate First, increase the hydrogen flow rate, point it to a fire, and then slowly return to work. This method is universal.
3.2 Reduce the flow rate of makeup gas First, reduce the flow of makeup gas. After ignition, re-adjust the working condition. This method is applicable to the situation where hydrogen is still used as a carrier gas, air is used as auxiliary gas, and makeup gas is used.
4 gas ratio adjustment Hydrogen flame gas chromatography gas flow ratio, the relevant information are recommended as follows: nitrogen: hydrogen: air = 1:1:10. However, due to the inaccuracy of the flow rate indicated by the rotameter, in fact, who will go to demand this ratio? I believe that for each gas to be well matched, the purpose is to have both a high detector sensitivity and a good separation effect, and it is not easy to turn off the flame.
In accordance with the above principles, the gas ratio should be adjusted according to the law.
4.1 Adjusting nitrogen flow rate After the column conditions are determined, the separation effect of the sample components is good or bad, and the nitrogen flow rate is the determining factor. When adjusting the nitrogen flow rate, the separation of the components should be observed until the nitrogen flow rate is as large as possible and the sample components are well separated.
4.2 Adjustment of Hydrogen and Air Flow The adjustment effect of hydrogen and air flow can be verified by the size of the base flow. Adjust the flow of hydrogen first to make it approximately equal to the flow of nitrogen, and then adjust the flow of air. When adjusting air flow, observe changes in base flow. As long as the base flow is increasing, it should still be adjusted to the contrary until the base flow no longer increases. Finally, increase the hydrogen flow slightly.
5 Injection technique In gas chromatography analysis, syringes or six-way valves are generally used for injection. When considering the injection technique, it is mainly aimed at syringe injection.
5.1 Injection volume The injection volume is related to factors such as gasification temperature, column capacity, and the instrument's linear response range. That is, the injection volume should be controlled to be able to instantaneously vaporize within the allowable range of the specified separation requirements and linear response. Filling column flushing method instantaneous injection volume: liquid sample or solid sample solution is generally 0.01 ~ 10μl, gas sample is generally 011 ~ 10ml, in the quantitative analysis, attention should be paid to accurate injection volume readings.
(1) Exclude all the air in the syringe. With a microsyringe to take a liquid sample, this can be done simply by repeatedly pumping the liquid into the syringe and quickly draining it back into the vial.
There is a better way to exclude all the air in the syringe. That is, replace the syringe 3 to 5 times with a sample about 2 times the planned injection volume. After each sample is taken, lift the syringe upright and the needle tip is facing up. Any air that remains in the syringe should run to the top of the needle. Push the syringe stopper and the air will be drained.
(2) Make sure the injection volume is accurate. Take a sample about 2 times the planned injection volume with the replaced syringe. Pick up the syringe vertically and put the needle upwards. Then let the needle pass through a layer of gauze so that it can be absorbed by the gauze from the needle tip. Discharged liquid. Push the syringe stopper until the desired value is read. Dry the needle tip with gauze. The exact liquid volume has been measured so far and it is necessary to pump air into the syringe. If the plunger is accidentally pushed, air can protect the liquid from being drained.
5.2 Injection method Take the syringe with both hands. Use one hand (usually the left hand) to insert the gasket against the needle, to inject a large volume sample (ie a gas sample) or when the input pressure is extremely high, to prevent the pressure from the gas chromatograph from ejecting the plunger (right thumb ).
Allow the tip of the needle to enter the inlet as deep as possible through the gasket, press the plunger for 1 to 2 seconds, and then withdraw the tip as quickly and steadily as possible (press the plunger still further).
5.3 Injection time The injection time has a great influence on column efficiency. If the injection time is too long, the chromatographic region will be widened and the column efficiency will be reduced. Therefore, for flushing chromatograms, the shorter the injection time, the better, and generally must be less than 1 second.
Analysis of Operational Skills of Gas Chromatograph
Gas chromatograph is the main tool to complete gas chromatographic analysis. However, in order to reflect the characteristics of simple operation and to achieve rapid and accurate analysis, operators must have good operating skills. Based on my experience in using gas chromatograph in the past two decades, I have developed gas chromatograph operation techniques for my colleagues.