Gas Chromatograph
Question 1: Why are some peaks tailing?
Answer: â‘ This may be due to the inlet or chromatographic column being dirty, or the chromatographic column being cut incorrectly. Cool the inlet, turn off the gas flow, and replace or clean the inlet parts, including the inlet liner and gold seal. Remove the column. Cut off a section of the column to remove non-volatile residue, septum debris, and seal ring fragments. The length of this column can be 1 inch to 1 meter, and can be longer if needed. Use the correct cutting tool to cut the column. If the cutting is not good, it may cause sample absorption. Use a soft abrasive such as a brass brush or alumina powder to scrub the steel inner wall of the inlet. Before reinstalling other components, make sure that the inlet has been cleaned. For the 5890, it is better to remove the split outlet line and clean with solvent.
â‘¡ When analysis is performed in splitless mode, a long splitless time may cause tailing. Usually the time should be in the range of 0.5 to 1 minute.
â‘¢Unpurged (dead) volume may also cause tailing. Make sure the column is installed correctly in the injector and detector.
â‘£If you consider the partial loss of the column, you can use the retention gap in front of the column (preparation column). If the efficiency of the column is not reduced, it can be cut or replaced, and the life of the column can be extended. However, it should be noted that the retention gap and the connection of the analytical column may cause leakage and sample absorption.
Question 2: How to improve the peak shape? (Front peak, tail peak)
Answer: The peak is due to the overload of the column. This may happen when the injection volume of one or more compounds exceeds the capacity of the column stationary phase. The thinner the liquid membrane, the less each compound remains in the column. This involves the injection volume and the compound concentration of each peak in the injection. The injection volume can be reduced by reducing the injection volume, splitting samples, or injecting samples with lower concentrations.
Question 3: What causes the peak to be larger than the original and appear earlier?
Answer: Excessively fast and large peaks are usually due to the reduction of the carrier gas discharged from the split port and 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 effluent and adjust the flow rate if you need to adjust the split ratio. If the problem persists, remove and clean the diverter. This problem may also be caused by a problem with the column head pressure regulating valve.
Question 4: When do I need to replace the septum or liner?
Answer: Usually better septa 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 that affect septum life are syringe size, inlet temperature, and pressure. Of course, the degree of pressure is relatively small. The factor that affects the life of the liner is usually the cleanliness of the sample. The specific procedures required for chromatography should be selected based on the instrument maintenance history.
Question 5: As the temperature of the sample chamber increases, does it affect the decomposition of the analyte?
Answer: If the compound has poor thermal stability, the decomposition of the analyte may cause some problems. This is relatively common in the pharmaceutical industry. If the thermal decomposition temperature of the drug or intermediate is lower than the inlet temperature, a special peak will appear in the analysis result or react with the target analyte.
Question 6: What is the best way to eliminate column bleed?
A: The best way to diagnose a chromatographic column for bleed problems is to first perform a blank chromatogram when installing the column under method conditions, and then compare the most recent run with a blank run chromatogram. If many peaks are generated during a blank run, the column performance changes, either because the carrier gas contains oxygen or because of sample residue. If you have a GC-MS, the typical leaching ions (such as DB / HP-1 or 5) for a low-polarity column will be m / z 207, 73, 281, 355, etc., most of which are epoxy alkyl.
Question 7: How do I know that the injection volume of the split / splitless inlet does not exceed the volume of the inlet liner reaction chamber?
A: This problem will not occur frequently if it is not caused by repeated injections. Accuracy problems are often caused by improper injection volumes. Because the inlet velocity of split injection is relatively high, the sample enters and exits the inlet much faster than splitless. Similarly, since the solvent does not have time to diffuse out of the liner, the split volume injection volume requirements are not so strict. In fact, 1 microliter is more appropriate, because reducing the split ratio is more effective for increasing the peak area than increasing the injection volume. However, splitless sampling is much more stringent and it is recommended to use a steam volume calculator to estimate the final diffusion volume.
Question 8: What is the best way to eliminate column bleed?
A: The best way to diagnose a chromatographic column for bleed problems is to first perform a blank chromatogram when installing the column under method conditions, and then compare the most recent run with a blank run chromatogram. If many peaks are generated during a blank run, the column performance changes, either because the carrier gas contains oxygen or because of sample residue. If you have a GC-MS, the typical leaching ions (such as DB / HP-1 or 5) for a low-polarity column will be m / z 207, 73, 281, 355, etc., most of which are epoxy alkyl.
Question 9: When the chromatographic analysis is running, the peaks of the standard and the sample are widened with time, is this normal?
Answer: If the retention time is not very different, just the tail of the broadened peak may indicate that there is an activation point. If the broadened peaks are symmetrical, it may be due to normal column "loss and loss". If the peak is extended, the column is overloaded.
Question 10: Why did my sample component peak appear in the blank run?
Answer: It may be due to sample preparation or system cleaning issues. Try to use new solvent in sample and blank sample preparation, and put new solvent in the sample wash bottle. Try using a new syringe and septum. Take out and clean the shunt outlet pipe. Run without injection to observe the presence of peaks on the heated column only.
Cast Iron Sink And Shower Tray
Cast iron sinks are used in kitchens of families and apartments. Grade A porcelain enamel is applied in our cast iron sinks. The package of Cast Iron Sink is individual wooden crate. We have sinks with 1 bowl or 2 bowls.
Body of Cast Iron Shower Tray is cast iron and we apply grade A porcelain enamel to the body. Package of cast iron shower tray is wooden pallet.
Cast Iron Sink And Shower Tray,Cast Iron Utility Sink,White Cast Iron Sink,Walk In Shower Tray
Anping Sunshine Sanitary Ware Co., Ltd. , https://www.sunshinebathtub.com