Gas chromatography

If it’s confirmed that there’s no issue with the gas circuit, what about the electrical circuit? Is the voltage stable?

If the problem persists even after turning off the heat, then the issue is likely not related to the detector. In that case, check the wiring system to see if there are any poor connections; this is mainly caused by excessive dust

Let’s take a look at the previous chromatography baseline graph. Your questions fall into several categories: gas source, column, injector, detector, power supply, and signal. Rule out the ideas one by one.

I also do gas chromatography analysis, so let me share my views. (1) Reasons for an unstable baseline and high noise include: 1. Problems with the workstation or processor itself; 2. The amplifier being damp or contaminated; 3. Poor grounding of the instrument; 4. Contamination of the chromatography column or excessive loss of material from it; 5. Impure gas; 6. A dirty sample; 7. A dirty glass liner; 8. The instrument operating at high sensitivity; 9. Excessive hydrogen flow, which can damage the voltage circuit due to polarization; 10. Too low a temperature of the detector, resulting in water accumulation on it; 11. High air flow, causing the flame to fluctuate; 12. A loose tungsten wire or poor contact; 13. A dirty nozzle; 14. Sample condensation at the heat-conduction vent; 15. Contamination of the electron capture detector; 16. Too low a temperature of the electron capture detector. Baseline noise check: 1. Install the chromatography column, turn on the instrument, adjust the operating conditions without injecting any sample, and observe whether the baseline remains flat within twice the retention time. 2. If baseline noise reappears, first check for air leaks at the injection port and column connector, etc. Are there any cavities at the head of the column bed? 3. The column stationary phase generally does not decompose; however, the elution or decomposition of high-boiling-point residues in the sample is also a fault that is difficult to eliminate. Re-sample after baseline noise is removed. If a detector is not used for an extended period of time and becomes damp, it will generate more noise, which can be resolved by heating. Contamination of the chromatography column also leads to increased noise, and this issue can be addressed through aging the column. Unstable voltage can likewise cause increased noise; stabilizing the voltage and ensuring proper grounding help to solve this problem. High levels of impurities in the air, carrier gas, and fuel gas, along with unstable pressures, can also result in such issues. First, since there is no voltage stabilizer connected to the power supply, have an electrician check the voltage of the power supply to see if it is within the normal range Is it properly grounded? 2. Do not inject sample; instead, collect the baseline signal directly. 3. There is suspicion of residues in the vaporization chamber or chromatography column. Check the baseline after turning off the hydrogen gas. If the baseline noise is high before and after FID ignition, the fault is likely unrelated to the chromatography column. 4. Disconnect the input signal of the N2000 workstation from the FID signal line, and short-circuit the workstation’s input signal line to capture the baseline; at this point, the noise level decreases significantly, indicating that the workstation is functioning properly. 5. Reconnect the input signal of the workstation to the FID signal line, and disconnect the signal line from the FID (so that there is no signal entering the FID amplifier). Then collect the baseline. Based on the spectrum, it seems that the issue lies with the FID amplifier; however, considering that failures of the amplifier are very rare, it is suspected that the problem is related to the power supply. It is also possible that the reduced voltage regulation capability of the microcurrent amplifier, which simulates a regulated power supply (±15V), is the main cause of increased amplifier noise; therefore, it is necessary to check whether normal operation can be achieved by using an external regulated power supply! Baseline check: 1. Try a different chromatography column. 2. Clean the detector. 3. Replace the gas. 4. Try using a gas cylinder with a different gas. 5. Poor contact in the signal lines or elsewhere, power supply interference, or poor grounding of the instrument, etc. 6. Remove the FID nozzle, shake it, and then put it back on.