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What are the precautions for using the gas chromatograph FID detector?

Time:2018/10/08   Pageviews:0    Share:
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A. Check that the gas chromatograph FID igniter is illuminated during the ignition sequence.20ml GC headspace vials

B. Verify that the ignition offset is less than or equal to 2.0 pA.

C. Check for leaks or partial blockage of the nozzle.

D. Check the gas chromatograph FID airflow rate. The ratio of hydrogen to air greatly affects the ignition. Non-optimal flow settings prevent flame ignition.

E. If the flame does not ignite, there may be a large leak in the system. Large leaks can cause the measured airflow rate to differ from the actual airflow rate, resulting in non-ideal ignition conditions. Thoroughly inspect the entire system for leaks, especially the column fittings at the FID of the gas chromatograph.

F. Check the gas chromatograph column flow rate.

G. Check for leaks at the FID column fittings.

H. Make sure the gas chromatograph FID temperature is high enough to ignite (greater than 150°).

FID can be said to be the common gas chromatograph detector used in the current Zui, and the use of FID is important to pay attention to safety, in order to get good performance and accurate results. This article mainly introduces the general use precautions of FID.

First, pay attention to safety when using FID detector

The primary consideration when using FID is safety:

1. Prevent hydrogen leakage.

Never allow hydrogen to leak into the column oven to prevent explosion. The specific operation is as follows: Do not pass hydrogen before the column and column are leak tested; check whether the hydrogen is off before unloading the column; if it is double FID, be sure to use another FID when working with only one FID The bulkhead screw is blocked.

2, to prevent burns.

The FID housing is very hot and should not be exposed to the surface to prevent burns.

Second, to maintain the performance of FID on the basis of security

1. Normal ignition.

At the time of ignition, the temperature of the FID must be above 120 °C. Ignition difficulties are mainly caused by improper adjustment of the three gases. Usually, the hydrogen flow rate is appropriately increased, or the gas flow rate is recommended according to the manufacturer's recommended gas flow rate. Whether the flame is lit with a cold metal shiny surface against the FID exit test, if there is water condensation on the surface, it indicates that it has been lit.

2. Prevent silica deposition.

The column of the polysiloxane stationary phase must be fully aged before use. When used, the column temperature should be as low as possible to avoid the formation of a silicon dioxide insulating layer on the nozzle and the two electrodes after the loss of the fixing liquid, so that the sensitivity is lowered, and the noise and drift are increased. If the silanized sample is analyzed for a long period of time, also pay attention to the silica deposition on the nozzle and electrode. If the phosphate sample is analyzed for a long time, there is also the possibility of contaminating the electrode.

3. Prevent condensation of water and so on.

To prevent condensation of water and other column effluents in the FID, first shut off the hydrogen, air, vaporization chamber temperature and column temperature, etc., after the FID heating and the entire gas phase system.

Third, in the case of stable FID performance, but also to ensure the reliability of the data 20ml GC headspace vials

1, linear range.

The linear range of FID can reach 10^7, but in the actual analysis, attention should be paid to the low-limit abnormality of the capillary column: the sample capacity of the capillary column is small, which limits the upper limit of the linear range of FID. Especially when analyzed with a small-diameter, thin liquid membrane capillary column, the column sample capacity is smaller. For example, the standard capillary column 25m*0.25mm*0.25μm Zui large column capacity is only 2-5*10^-8g, with FID detection limit of 10^-12g, the linear range is only 10^4. Therefore, when using capillary column analysis, pay attention to the linear range that is actually reachable under the analysis conditions, otherwise it will bring a lot of error.

2. Flow rate measurement.

The outer casing of the FID is now sealed, with only one outlet. Carrier gas, hydrogen and air are discharged from this outlet. If you want to measure the flow rate of air or hydrogen, then the column is connected and the carrier gas is passed. Note that after the total flow rate is measured, the carrier gas flow rate is subtracted when calculating the hydrogen or air flow rate. Also note that the flow rate is temperature dependent and should be measured or compared at the same temperature setting. 20ml GC headspace vials

This is the end of the introduction of What are the precautions for using the gas chromatograph FID detector? I hope it can help you.


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