For the frequent failures of the gas chromatograph, summarize these faults as follows: 1: Why do some peaks appear to be tailed? A: 1 This may be due to an unclean inlet or column, or incorrect column cutting. Cool the inlet, turn off the airflow, and replace or clean the inlet components, including the inlet liner and the gold seal. Remove the column. Cut off a column to remove non-volatile residues, septum debris, and seal debris. This column can be from 1 inch to 1 meter in length and can be longer if needed. Use the correct cutting tool to cut the column. If the cut is not good, it may cause the sample to absorb. Use a soft abrasive such as a brass brush or alumina powder to scrub the inlet steel inner wall. Make sure the inlet is clean before reinstalling other components. For the 5890, it is a good idea to remove the split outlet line and clean it with solvent. 2 When analyzing in the splitless mode, long split time may cause smearing. Usually the time should be in the range of 0.5 to 1 minute. 3 Unpurged (dead) volume can also cause tailing. Make sure the column is installed correctly in the injector and detector. 4 If you consider partial loss of the column, you can use the retention gap in front of the column (prepare the column). If you do not reduce column efficiency, you can cut or replace it and extend the life of the column. However, care should be taken to preserve the gap and analyze the column connections that may cause leakage and sample absorption. 2: How to improve the peak shape? (Front peak, trailing peak) A: The peak is due to overload of the column. This can occur when the injection volume of one or more compounds exceeds the column stationary phase capacity. The thinner the liquid phase film, the less each compound remains in the column. This involves the injection volume and the concentration of the compound at each peak in the injection. The injection volume can be reduced by reducing the amount of injection, split sample, or sample with a lower injection concentration. 3: What causes the peak to be larger than the original, and it appears early? A: The too fast, too large peak is usually due to the reduction of the carrier gas discharged from the split port and the septum purge port, and more into the column; therefore, increasing the head pressure can reduce the split ratio. Check the gas flow rate of the split product. If you need to adjust the split ratio, adjust the flow rate. If the problem persists, remove and clean the split vent. This problem may also be caused by a problem with the column head pressure regulating valve. 4: When do I need to replace the septum or liner? A: Usually a good septum can guarantee at least 100 injections without problems. When the chromatographic characteristics indicate a problem with the liner, the liner needs to be replaced. Factors affecting the life of the septum are syringe size, inlet temperature and pressure, and of course less affected by pressure. The factor that affects the life of the liner is usually the cleanliness of the sample. The specific procedure required for chromatography should be selected based on the instrument maintenance history. 5: As the temperature of the injection chamber rises, does it affect the decomposition of the analyte? A: If the compound is poorly thermostable, analyte decomposition can cause problems. This is more common in the pharmaceutical industry. If the drug or intermediate thermal decomposition temperature is below the inlet temperature, a special peak will appear in the analysis or react with the analyte of interest. 6: What is the main method to eliminate the column churn problem? A: The primary method for diagnosing column chorage problems is to make a blank chromatogram when the column is first installed under the method conditions, and then compare the most recent run to the blank run chromatogram. If a lot of peaks are produced during a blank run, the column performance changes, either because the carrier gas contains oxygen or because of sample residue. If there is GC-MS, the typical loss ion (such as DB/HP-1 or 5) of the low polarity column will have a mass/charge ratio m/z of 207, 73, 281, 355, etc., most of which are cyclosiloxane. alkyl. 7: How do I know that the injection volume of the split/splitless inlet does not exceed the volume of the inlet liner chamber? A: If it is not repeated for multiple injections that cause accuracy problems, this problem will not happen often. Accuracy problems are often caused by improper injection volumes. Because the inlet flow rate of the split injection is relatively high, the sample inlet and outlet is much faster than the splitless injection. Similarly, the split mode injection volume requirements are less stringent because the solvent does not have time to diffuse out of the liner. In fact, 1 microliter is more suitable, because reducing the split ratio is more effective than increasing the peak area than increasing the injection volume. However, the splitless injection requirements are much more stringent, and it is recommended to use the vapor volume calculator to estimate the final diffusion volume. 8: What is the way to eliminate the column drain problem? A: The primary method for diagnosing column chorage problems is to make a blank chromatogram when the column is first installed under the method conditions, and then compare the most recent run to the blank run chromatogram. If a lot of peaks are produced during a blank run, the column performance changes, either because the carrier gas contains oxygen or because of sample residue. If there is GC-MS, the typical loss ion (such as DB/HP-1 or 5) of the low polarity column will have a mass/charge ratio m/z of 207, 73, 281, 355, etc., most of which are cyclosiloxane. alkyl. 9: When the chromatographic analysis is running, the peaks of the standards and samples are widened over time. Is this normal? A: If the retention time is not very different, just the widened peak tail may indicate an activation point. If the broadened peak is symmetrical, it may be due to normal column "loss and loss." If the peak is extended, the column is overloaded. 10: Why did my sample component peak appear in the blank run? A: It may be due to sample preparation or system cleaning problems. Try to use a new solvent in the sample and blank sample preparation and install a new solvent in the sample wash bottle. Try using a new syringe and septum. Remove and clean the split outlet line. Run without injection to see if only the heated column is peaked. 10: What causes baseline instability and interference? Answer: 1. The syringe is contaminated. Clean the syringe; do a concentration test and the carrier gas line may also be cleaned. 2. The column is contaminated. Bake the column for a time limit of 1-2h. 3. The detector is not balanced. The detector typically takes 24 hours to get balanced. 4. Change the carrier gas flow rate during programming (in many cases normal). 11: What causes excessive baseline noise? Answer: 1. The syringe is contaminated. Clean the syringe; do a concentration test and the carrier gas line may also be cleaned. 2. The column is contaminated. Bake the column for a time limit of 1-2h. 3. The detector is not balanced. Cleaning the detector, usually the noise does not suddenly increase but gradually. 4. Pollution or carrier gas quality is reduced. Use a high quality carrier gas or check for leaks. It usually happens suddenly when the gas cylinder is replaced. 5. The column is installed too much. Can be reinstalled. 6. The carrier gas flow rate is not suitable. Reset the flow rate. 7. Vulnerabilities occur when used in conjunction with MS, ECD, and TCD to find and eliminate vulnerabilities. 8. The detector's lamp or electron multiplier tube is aged. 12: 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, and the evaporation or compositional changes of the sample may be caused. 3. The column is contaminated. 13: If the resolution drops, what should I do? Answer: 1. The column temperature is different. Check the column temperature. 2. Dimensions and phases of different columns. Verify the characteristics of the column. 3. Change the carrier gas flow rate. 4. The column is contaminated and the column is cleaned with a solvent. 5. The change of the injector. Check the injector settings. 6. Changes in the concentration or solubility of the sample. Try a different concentration. 14: What happens if there is a split peak? A: 1. Try changing the injection method. 2. Change the solvent to make it a single solvent. 3. Reinstall the column. 4. Reduce the injection temperature. 15: What kind of test should I use if I suspect that the injector or carrier gas is contaminated? Answer: 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 to the first map. 6. If at the first time, the peak map contains a large number of peaks and the baseline is unstable, it implies that the capillary column is contaminated (the injector or carrier gas is contaminated). 7. If both chromatograms contain a small number of peaks or small drifts in the baseline, then the injector or carrier gas can be assumed to be relatively clean. Suppose 8. If both chromatograms contain significant amounts of noise and/or baseline drift, it usually indicates that the injector or carrier gas is contaminated. 16: How long should the guard column be? A: The representative guard column length is 0.5-10m. Although not a certain length is suitable for all samples, the following suggestions are also available. If the sample is relatively pure, the solute is polar, the guard column should be between 0.5 and 1.0 m; if the sample is relatively impure, the guard column should be suitably longer. 5-10m long is mainly for the maintenance of a single system. The long guard column allows the user to subtract approximately 1 m instead of the entire guard column.
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