How Often does the Gas Chromatograph Septum be Replaced?

The replacement of the gas chromatography septum needs to be determined according to the performance of the instrument itself and the number of samples to be tested. After a batch of samples is normally completed, check whether the connection between the chromatographic column and the injection port is leaking due to damage to the septum and causing peaks. Abnormal, the septum must be replaced at this moment. If the number of samples is small, several samples are analyzed in a few days, and the septum is not damaged, causing air leakage, etc., it can be used for 1 to 2 months. If the sample amount is large, one batch Make hundreds of them. It is recommended to check the condition of the septum after finishing, and replace it immediately. You can learn more about the following:

The gas chromatograph injection port septum, abbreviated as the injection pad, is one of the key components for introducing the sample into the chromatographic column in the gas chromatograph analysis test.

During the sampling process of the gas chromatograph, only when the carrier gas pressure in the chromatographic column reaches a certain height, the sample to be tested can flow through the chromatographic column with the airflow. Here, the function of the sampling pad is to keep the gas chromatograph system in a sealed state on the one hand, to isolate the sample flow path from the outside to prevent air from entering the system or sample leakage; on the other hand, to keep the internal pressure of the chromatograph system stable.

Sampling pad is generally made of high temperature resistant and airtight silicone rubber. The standard for selecting the injection port septum is usually based on the upper limit temperature detected by the gas chromatograph. Generally speaking, the injection cushion with a lower temperature limit is softer and has good sealing performance. Compared with the pad, the puncture resistance (sample injection) is better. However, if the injection pad is used at a higher temperature, the injection pad may leak or decompose.

The sampling pad is a wearable accessory in the gas chromatograph analysis system. After a period of use, air leakage or other abnormal phenomena may occur.

The effects of damage to the sampling pad are as follows:

1. Air leakage, during the gas chromatograph detection and injection process, the syringe will cause a certain degree of damage to the injection pad and cause air leakage;

2. Decomposition. When the chromatographic column separates some samples with high boiling points, the column temperature will be relatively high. At this time, the sample pad will be slightly decomposed at high temperature;

3. Sample loss, once the sampling pad is damaged and leaks, the sample will be lost;

4. The flow rate in the chromatographic column decreases and the column efficiency decreases. When the sampling pad leaks or is decomposed, the pressure inside the chromatographic column becomes unstable, which reduces the carrier gas flow in the column and the resolution of the chromatographic column;

5. The peak output is abnormal. Once the resolution of the chromatographic column is affected, the electrical signal of the substance detected by the detector will be lost, and the formed chromatogram will be abnormal and ghost peaks will be formed. The performance of the sampling pad affects the test results of the gas chromatograph. Therefore, when the sampling pad is damaged, it should be replaced in time. So when should the gas chromatograph sampling pad be replaced?

In addition to the above phenomena, the TCD detector can also be used to detect. If there is no sample injection, there are regular small peaks on the recorder, indicating that the septum is leaking and it is time to replace it. Do not tighten the septum too tightly. Generally, the replacement is done at room temperature, and it will become tighter when the temperature rises. If the septum is tightened too tightly, it will be difficult to inject the sample and easily bend the syringe needle. Although the sampling pad is a very small accessory in chromatographic analysis, a little attention can reduce the damage to it during use. How to reduce the septum loss problem? 1. Use it in the high temperature range of the septum .

The sampling pad is generally made of silicone rubber. Silicone rubber has higher heat resistance than ordinary rubber. It can be used almost forever at 150°C without performance changes; it can be used continuously at 200°C for 10,000 hours; It can also be used for a period of time at 350 degrees. Therefore, the selection of the sampling pad must take into account the high temperature limit of the gas chromatograph to analyze the sample, and try to use it within the temperature limit, so as to avoid overheating decomposition; 2. Try to use the autosampler as much as possible to reduce the damage to the sampling pad; 3. Use a sharp-pointed syringe to reduce the force-bearing area.