Fault analysis and application of the hottest gas

Fault analysis and application of gas chromatograph

Abstract: This paper focuses on the fault analysis and troubleshooting of gas chromatograph, for the reference of personnel engaged in the maintenance and use of gas chromatograph

key words: gas chromatograph; Fault; Chemical analysis

1 preface

gas chromatograph is a widely used organic multicomponent chemical analysis instrument. It has the advantages of high separation efficiency, fast analysis speed, less sample consumption and multi-component measurement. It plays a very important role in chemical analysis. Nearly 80% of the tasks of central control of raw materials and product analysis are completed by gas chromatography. However, due to the quality of personnel, the nature of samples and the instrument itself, there are often various analysis failures, which seriously affect the normal production analysis

therefore, it is very important to master an accurate and fast method of troubleshooting the instrument

2 composition of chromatograph

it is very important for a chromatographic analyst to master the structural principle of chromatograph and the function of each part. General gas chromatograph is composed of gas circuit part and circuit part, mainly including: gas generator injection system, separation system, detection system, data processing system

3 common faults and troubleshooting of gas chromatograph

3 1 incomplete separation

① several peaks overlap and cannot be separated. Treatment method: reduce the flow rate of carrier gas, reduce the injection volume, and reduce the column temperature. For those that can be completely separated but cannot be completely separated after a period of use, it indicates that the fixed liquid has been lost and the service life of the chromatographic column has expired, so the fixed liquid needs to be replaced

② too long separation time flattens the peak of late distillation. Treatment method: it can be solved by increasing the column temperature

and more and more new products are entering the market ③ the sensitivity of the detector is too low to detect components with small content. Treatment: it can be solved by increasing the injection volume and improving the sensitivity of the detector

3. 2. Irregular peak shape

① tailing peak appears. Treatment method: use strong polar stationary solution, eliminate the activity of the support and improve the column temperature

② flat topped or serrated peaks appear. Nowadays, the solution is to reduce the injection volume, increase the column temperature and carrier gas flow rate. In addition, when the amplifier input is saturated, a flat peak will also be formed

3. 3. The influence caused by the detector, take TCD as an example

thermal conductivity detector TCD uses the different thermal conductivity of carrier gas and measured gas to detect that the unbalanced voltage generated in the bridge is proportional to the concentration of the measured component, so as to realize the measurement of the measured component. ① Contamination of TCD detector will cause baseline drift or stepped baseline, and may cause high noise. ② TCD thermal resistance wire is burnt out, and the baseline is reduced to zero. ③ TCD power supply is not because bubbles enter the quantitative tube and are stable, with irregular pulse interference peaks

3. 4 Influence of carrier gas

the carrier gas carries the analytical sample through the stationary phase, and the separated gas is carried out of the chromatographic column one by one by the carrier gas over time and sent to the detection part for detection. Operating conditions such as the flow rate of carrier gas, the nature of carrier gas and the influence of carrier gas pressure will affect the chromatographic separation efficiency. ① If the carrier gas flow is low, the retention time will increase, the sensitivity will decrease, or there will be round peaks and tailing peaks. ② High carrier gas flow will cause high noise or component separation. ③ The carrier gas control is unstable, resulting in irregular baseline drift or wavy baseline drift

under the above conditions, check whether the pressure reducing valve exceeds the scope of use, replace the pressure reducing valve if necessary, and then check whether there is air leakage in the carrier gas

3. 5. Circuit problems

circuit faults are generally easy to judge, such as the power supply does not start, the detector and injection port are not heated, and the thermostat cannot be constant temperature, etc. If there is a periodic sine wave in the baseline, it is caused by the failure of the amplification circuit; The treatment method is generally to replace the damaged electronic components

3. 6 other

gradually approach 20% of the rated load in daily analysis (if 20% of the 2000kN press is 400.0kn, the problems not discussed above will also be encountered. If the hydrogen flame detector does not ignite, first determine whether the hydrogen and air have been turned on, and then confirm whether the ignition coil is easy to use. If these three conditions are met or not, it may be the gas leakage at the joint between the detector and the chromatographic column; for the case of peak inversion, it may be that the polarity of the host or processor is reversed. In this case, you can check it first Polarity of the instrument; If the injection volume is inconsistent with the integral area, the output signal line is likely to be connected incorrectly

4 Conclusion

the above discussion is about several common faults in gas chromatography and their troubleshooting methods, but in specific work, there are often complex situations in which several faults coexist, which requires careful analysis and judgment according to the symptoms of the faults, and then use the above methods to eliminate the faults one by one to restore the instrument to normal. (end)