Question 1: What causes baseline instability and interference?
Answer: 1. The syringe is contaminated. Clean the injection needle; for a concentration test, the carrier gas line may also be cleaned.
2. The column is contaminated. Bake the column for a limited time of 1-2h.
3. The detector is unbalanced. The detector generally needs 24h to be balanced.
4. Change the carrier gas flow rate during the program temperature increase (normal in many cases).
Question 2: What causes excessive baseline noise?
Answer: 1. The syringe is contaminated. Clean the injection needle; for a concentration test, the carrier gas line may also be cleaned.
2. The column is contaminated. Bake the column for a limited time of 1-2h.
3. The detector is unbalanced. Cleaning the detector, usually the noise is not suddenly increased but gradually generated.
4. Pollution or reduced carrier gas quality. Use high-quality carrier gas or check for leaks. It usually happens suddenly when changing the carrier gas cylinder.
5. The post is installed too far. Can be reinstalled.
6. The carrier gas flow rate is inappropriate. Reset the flow rate.
7. Vulnerabilities occur when used in conjunction with MS, ECD, TCD, just find and eliminate the vulnerabilities.
8. The detector lamp or electron multiplier tube is aging.
Question 3: What causes the peak shape to change?
Answer: 1. The detector response changes. Check gas flow rate, temperature and settings.
2. The concentration of the sample changes. Check and check the concentration of the sample, evaporation of the sample or changes in composition may cause it.
3. The column is contaminated.
Question 4: What if the resolution drops?
1. The column temperature is different. Check the column temperature.
2. The dimension and phase of different chromatographic columns. Verify the characteristics of the column.
3. Change the carrier gas flow rate.
4. The chromatographic column is contaminated. Use solvent to clean the column.
5. Changes to the injector. Check the settings of the injector.
6. Changes in sample concentration or dissolving power. Try a different concentration.
Question 5: How to deal with split peaks?
1. Try to change the sampling method.
2. Change the solvent to make it a single solvent.
3. Reinstall the column.
4. Reduce the injection temperature.
Question 6: If it is suspected that the injector or carrier gas is contaminated, what kind of test should be used?
1. The GC is kept at 40-50 ° C for 8 hours or more.
2. Run a blank analysis (turn on the GC, but do not inject).
3. Collect the chromatogram of the blank analysis.
4. Start the second time immediately after the completion of the first blank analysis. The interval between the two should not exceed 5 minutes.
5. Collect the chromatogram of the second blank analysis and compare it with the first spectrum.
6. If the peak image contains a large number of chromatographic peaks at the first time, and the baseline is unstable, it indicates that the capillary column is contaminated (the injector or carrier gas is contaminated).
7. If both chromatogram peaks contain a small number of peaks or small drifts in the baseline, then it can be assumed that the injector or carrier gas is relatively clean. if
8. If both chromatogram peaks contain significant amounts of noise and / or baseline drift, it usually indicates contamination of the injector or carrier gas.
Question 7: How long should the guard column be?
The length of the representative guard column is 0.5-10m. Although there is no specific length suitable for all samples, the following suggestions can also be used for reference. If the sample is relatively pure and the solute is polar, the guard column should be between 0.5-1.0m; if the sample is relatively impure, the guard column should be longer. The 5-10m length is mainly for maintaining a single system. The long guard column allows the user to subtract approximately 1m and replace the entire guard column installation.
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