Gas chromatograph's common trouble and elimination method

1 Gas chromatograph is a widely used organic multi-component chemical analysis instrument. It has the advantages of high separation efficiency, fast analysis, few samples, and multi-component measurement. In the chemical analysis, it occupies a very important position. Nearly 80% of raw material control and product analysis tasks are completed by gas phase color. However, due to the nature of personnel quality samples and the instrument itself, there are often such analysis failures that 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 master the structural principles of the chromatograph and the role of each part. General gas chromatogram gas path and circuit components, including: gas generator; sampling system; separation system; detection system, 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. If the original separation can not be completely separated after a certain period of time, it indicates that the fixed solution has been lost and the column life is over. It is necessary to replace the fixed solution.

2 The separation time is too long to make the peak of the evening distillation. 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: Through the sample, improve the sensitivity of the detector to solve.

3.2 Peak shape irregularity 1 tail peak. Treatment method: Use a strong polar fixative to eliminate the activity of the support and increase the column temperature.

2 Flat tops or peaks appear. 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 influence of the detector, using TCD as an example The thermal conductivity detector TCD uses different thermal conductivity of the carrier gas and the measured gas. The unbalanced voltage generated in the detection bridge is proportional to the concentration of the measured component, so as to achieve Measuring the composition of the measurement.

1TCD detector is contaminated by baseline drift or a graded baseline appears and may be highly noisy.

2TCD thermal resistance wire was blown and the baseline dropped to zero.

3TCD power supply instability, out of pulse interference peak.

3.4 Influence of carrier gas The carrier gas carries the analytical sample through the stationary phase. The separated gas is carried one by one by the carrier gas and is sent out to the detection section. Operational conditions such as carrier gas flow, carrier gas properties, and carrier gas pressure can affect chromatographic separation performance.

A low amount of 1 will cause the retention time to increase, the sensitivity to decrease or the peak of the dome and trailing peak.

2 If the carrier gas flow is too high, it will cause high noise or component separation without carrier gas control instability, resulting in irregular baseline drift or wave-like baseline drift.

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 faults are generally easier to judge, such as the power supply does not start, the detector, the inlet is not heated, the thermostat can not be constant temperature and so on. If the sine wave appears on the baseline, it is due to a fault in the amplifier circuit; processing methods generally replace damaged electronic components.

Other problems encountered in the above-mentioned daily analysis may be encountered. For example, if the hydrogen flame detector does not ignite, it is necessary to determine whether hydrogen gas has been turned on and whether it is easy to use the ignition coil. If these three conditions are satisfied, If it does not ignite, it may be leaks at the detector and column fittings; for inverted conditions, the polarity of the host or processor may be reversed. In this case, the polarity of the instrument may be checked first; The situation where the injection volume does not match the integrated area may connect the output signal line to the wrong one.

4 concluding remarks The above discussion is a few kinds of common faults in gas chromatograph analysis and its elimination method, but in the concrete work often several kinds of breakdowns coexist the situation, this needs to carefully analyze and judge according to the symptom of the breakdown, and then uses the above-mentioned method one by one Troubleshooting will restore the instrument to normal.