Fault Analysis and Practical Application of Gas Chromatograph
Abstract: The gas chromatograph is a widely used instrument, because the quality of personnel or the quality of the instrument itself will produce a lot of problems. This article focuses on the analysis and troubleshooting of gas chromatographs for reference by personnel engaged in the maintenance and use of gas chromatographs. The carrier gas carries the analysis sample through the stationary phase , and the separated gas is carried one by one by the carrier gas and then sent out to the detection column for detection. Operational conditions such as carrier gas flow, carrier gas properties, and carrier gas pressure can affect chromatographic separation performance. 1 The carrier gas flow rate is too low , which will cause the retention time to increase , the sensitivity to decrease or the dome peak and trailing peak. â‘¡ high carrier gas flow rate, or may cause high noise components can not be separated points. 3 Unsteady carrier gas control , resulting in an irregular baseline drift or wavy baseline drift. Round Head Mat,AB Mat,Mat Jiangsu Laiao Material Technology Co., Ltd. , https://www.laiaomaterial.com
　　　　
　 1 Introduction
　　
　　 Gas chromatography is a widely used organic multi-component chemical analysis instrument. It has the advantages of high separation efficiency , fast analysis speed, small amount of sample, and multi-component measurement. It occupies a very important position in chemical analysis. Nearly 80% of raw material control and product analysis tasks are performed by gas chromatographic analysis. However, due to the nature of personnel quality samples and the instrument itself, it often occurs that such analysis failures seriously affect the normal production analysis.
　　
Therefore, it is very important to master an accurate and rapid method of troubleshooting the instrument.
　　
2, the composition of the chromatograph
　　
For a chromatographer , it is important to be proficient in the structure of the chromatograph and the role of each part. The general gas chromatograph is composed of the gas path part and the circuit part , mainly including: the gas generator sampling system separation system detection system and data processing system.
　　
　 3. Common Faults and Removal Methods of Gas Chromatograph
　　
　　 3.1 Incomplete separation
　　
1 Several peaks overlap and cannot be separated. Treatment method: reduce the carrier gas flow rate , reduce the injection volume , and reduce the column temperature. For the original separation, it will not be completely separated after a period of use, indicating that the fixed solution has been lost, the column life is over, and the fixed solution needs to be replaced.
　　
2 The separation time is too long to flatten the late-distilled peak. Treatment method: It can be solved by increasing the column temperature.
　　
3 The detector sensitivity is too low to detect components with low levels. Treatment method: It can be solved by increasing the injection volume and increasing the sensitivity of the detector.
　　
　　 3.2 Irregular peak shape
　　
A trailing peak appears. Treatment method: Use a strong polar fixative solution to eliminate carrier activity and increase column temperature.
　　
2 A flat top or sawtooth peak appears. Treatment method: Solve by reducing injection volume, increasing column temperature and carrier gas flow rate. In addition, flat peaks are formed when the amplifier input is saturated.
　　
　　 3.3 The effect of detectors , using TCD as an example
　　
Different thermal conductivity detector TCD carrier gas and thermal conductivity of the gas to be measured, is proportional to the unbalanced voltage detecting bridge sample concentration generated to achieve measurement of the component being tested. Contamination of the 1TCD detector can cause baseline drift or a stepped baseline , and can be highly noisy. 2TCD thermal resistance wire was blown and the baseline dropped to zero. 3TCD power supply instability , irregular pulse interference peak.
　　
　 3.4 Effect of Carrier Gas
　　
　　
The above situation should check whether the pressure relief valve exceeds the scope of use , if necessary, replace the pressure relief valve , and then check the carrier gas for leaks.
　　
　　 3.5 Circuit Problems
　　
Circuit failure is generally easier to judge , such as the power does not start , the detector, the inlet is not heated , the thermostat can not be constant temperature and so on. If the baseline appears a periodic sine wave , it is due to a fault in the amplifier circuit ; processing methods generally replace damaged electronic components.
　　
　 3.6 Others
　　
In the daily analysis will encounter the above-mentioned issues have not been discussed , such as the hydrogen flame detector does not fire , first of all to determine whether you have opened hydrogen and air , and then confirm the ignition coil is easy to use , if these three conditions are available or does not fire, the detector may be column leakage joints; for peak occurs inverted polarity may be a host processor or the reverse, in which case, polar check the instrument; for If the injection volume does not match the integrated area , it is very likely that the output signal lines are connected incorrectly.
　　
　 4 Conclusion
　　
The above discussion is a few kinds of common faults in gas chromatographic analysis and their exclusion methods , but in the specific work often there are several kinds of fault coexistence of the complex situation , which requires careful analysis and judgment based on the symptoms of the fault , and then use the above method to eliminate one by one Fault , make the instrument return to normal.