Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

GW MB10F 0.8A 1000V rectifier bridge

Supply 1206 blue light 1206 blue LED quality assurance original authentic large number

Brand AVX TPSE226M035R0125 Low impedance tantalum capacitor AVX 22

What should you pay attention to when operating a gas chromatograph? Tips for using a gas chromatograph

Gas Chromatograph is a commonly used analytical instrument. In addition to quantitative and qualitative analysis, it can also determine the physical and chemical constants such as partition coefficient, activity coefficient, molecular weight and specific surface area of ​​the sample on the stationary phase. Biochemistry, medical and health, food industry, environmental protection and other aspects are widely used. Today we mainly introduce the use of gas chromatographs, hoping to help users better apply the product.

1 heating

The way the temperature is given is different because of the manufacturer and quality of the gas chromatograph. For the given temperature by the microcomputer setting method or the dial selection method, it is generally set directly or select a suitable temperature value to increase the temperature. And if you use the knob positioning method, there are skills.

1.1 Over temperature positioning method

Adjust the temperature control knob to about 30 ° C below the operating temperature and warm the gas chromatograph. When the temperature is too high to about the operating temperature, match the temperature indication and the heating indicator, and then gradually adjust the temperature control knob to the appropriate position.

1.2 step-by-step progressive positioning method

Turn the temperature control knob to an angle of the heating direction, the temperature rise starts, the indicator light is on; when the temperature is basically stable, turn the temperature control knob in the same direction to start to heat up; so adjust the adjustment until the constant temperature is at the working temperature.

2 pool balance

The balance of the pool is actually the balance of the heat-conducting conductive bridge, so that it has a more suitable output. The adjustment technique is actually a gas chromatograph with adjustment functions such as pool balance, zero adjustment and record zero adjustment.

In the first step, use the cell balance or zero adjustment knob to adjust the recorder pointer to the appropriate position;

The second step is to attenuate to about 16 times and observe the movement of the pointer of the recorder;

In the third step, use the record zero knob to adjust the recorder pointer back to the original position;

The fourth step is to return the attenuation and observe the movement of the recorder pointer;

In the fifth step, use the zero adjustment or the pool balance knob to return the recorder pointer to its original position.

3 ignition

The hydrogen flame gas chromatograph requires ignition when it is turned on, and sometimes it needs ignition after various reasons. However, we often encounter situations where ignition is not possible. Here are two ignition techniques for the peers to try.

3.1 Increase the hydrogen flow method

First increase the hydrogen flow rate, and then slowly return to the working condition after the fire. This method is common.

3.2 Reduce the tail gas flow method

First reduce the flow of the makeup gas, and then return to the working condition after the fire. This method is applicable to the case where hydrogen is still used as the carrier gas and air is used as the assist gas and the tail gas.

4 gas ratio adjustment

The flow ratio of the three gas of the hydrogen flame gas chromatograph is recommended: nitrogen: hydrogen: air = 1: 1:10. However, because the rotameter indicates the inaccuracy of the flow, who is going to demand this ratio? I think that the gas is well matched, and the purpose is to have both high detector sensitivity and good separation. The effect is not easy to turn off.

In accordance with the above principles, the gas ratio should be adjusted according to the following method.

4.1 Adjustment of nitrogen flow rate

After the column conditions are determined, the separation effect of the sample components is good or bad, and the flow rate of nitrogen is the determining factor. When adjusting the nitrogen flow rate, the separation of the components should be observed by injection 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 effect of hydrogen and air flow can be checked by the size of the base flow. The hydrogen flow rate is first adjusted to be equal to the flow rate of the nitrogen gas, and then the air flow rate is adjusted. When adjusting the air flow, observe the change of the base flow. As long as the base flow is increasing, it should still be adjusted in phase until the base flow no longer increases. Finally, increase the hydrogen flow rate a little.

5 injection technology

In gas chromatography analysis, it is generally injected using a syringe or a six-way valve. When considering the injection technique, it is mainly based on syringe injection.

5.1 injection volume

The injection volume is related to factors such as gasification temperature, column capacity, and the linear response range of the instrument. That is, the injection volume should be controlled within the allowable range of the specified separation requirements and linear response. The instantaneous injection volume of the packed column flushing method: the liquid sample or the solid sample solution is generally 0.01 to 10 μl, and the gas sample is generally 011 to 10 ml. In the quantitative analysis, it should be noted that the injection volume reading is accurate.

(1) Exclude all air in the syringe

This can be done by taking a liquid sample with a microsyringe as long as the liquid is repeatedly pumped into the syringe and quickly discharged back to the sample vial.

There is also a better way to exclude all the air in the syringe. That is to replace the syringe 3 to 5 times with about 2 times the planned injection volume. After each sample is taken, the syringe is picked up vertically with the needle tip 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) Ensure the accuracy of the injection volume

Use a replaced syringe to take about 2 times the planned injection volume, lift the syringe vertically, point the needle up, and let the needle pass through a layer of gauze so that the gauze can be used to absorb the liquid discharged from the tip. Push the syringe stopper until the desired value is read. Dry the tip with gauze. At this point, the exact volume of the liquid has been measured and it is necessary to pump the air into the syringe. If the plunger is inadvertently pushed, the 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 needle into the needle, inject a large volume of sample (ie a gas sample) or when the input pressure is extremely high, prevent the pressure from the gas chromatograph from ejecting the plunger (with the thumb of the right hand) ).

Let the tip of the needle pass through the shims as far as possible into the inlet, press the plunger for 1 to 2 seconds, then pull the tip as quickly and steadily as possible (continue to hold the plunger).

5.3 Injection time

The length of injection time has a great influence on column efficiency. If the injection time is too long, the chromatographic area will be widened to reduce column efficiency. Therefore, for flush chromatography, the shorter the injection time, the better, generally less than 1 second.