How to clean the injection port of liquid chromatography

In the process of injection, the injection valve must be very clean, otherwise better results can not be obtained. After the injection valve is switched to the injection position (inject), it should be kept in this position for a period of time, so that the mobile phase can fully flush the sample quantitative tube, which can not only ensure high accuracy, but also does not need to flush the sample quantitative tube. This kind of washing controlled by chromatograph is obviously better than manual washing. Note: The volume of mobile phase required for cleaning is at least 10 times of the sample volume. For example, take 20μL of sample in 100μL sample measuring tube, and the flow rate of mobile phase is 1mL/min, then at least 12s should be kept at the injection position, that is, 20μ l×11000μ lmin-650. When the sample quantitative tube is completely flushed, the rotary handle can be turned back to the sampling position (loading) or kept in the sampling position until the next sampling. When switching back to the sampling position, pull out the sample injection needle or micro sample injection needle from the injection valve. In order to prevent cross contamination, it is not necessary to flush the injection needle inlet of the injection valve after each injection. The injection valve is directly connected to the injection hole according to the patented design, so that the front end of the injection needle can be directly connected to the end of the sample quantitative tube, and there will be no other sample residual space. In this way, during the next injection, the last residual sample will not enter the sample quantitative tube. However, in the process of inserting or pulling out the injection needle, a small amount of samples will be deposited in the sealed area of the needle. Accurate determination showed that the residue was 1nL ~ 10nL. This shows that when 20μL sample is injected, there will be 0.005% ~ 0.05% residue. After each injection, these residues can be removed by flushing the inlet of the injection needle. The process of washing the injection needle inlet is as follows: set the flow rate of mobile phase to 0.1ml/min ~1ml/min, connect the injection needle inlet washing head (Rheodyne part number 7 125-054) to a relatively large syringe, and only wash the injection needle inlet with a large amount of mobile phase at the injection position. In this way, the liquid entering the injection valve bypasses the sample quantitative tube and is discharged from the 5# port of the sample overflow tube. This process can thoroughly clean the injection needle inlet, catheter, injection needle inlet tube and injection needle sealing ring. However, the cleaning method using an inserted syringe cannot completely clean the surfaces of the above components. When the injection needle is inserted into the injection needle inlet of the injection position, the needle pushes a small amount of sample liquid in the injection needle sealing ring (left by the last cleaning of the injection needle inlet tube) into the sample quantitative tube. When the composition of the sample solution is different from that of the mobile phase used, strange peaks may appear on the highly sensitive detector by partially filling the quantitative tube. Therefore, it is best to clean the injection needle with mobile phase. If serious cross-contamination has been found, please check whether it is caused by the following reasons: ⅰ. The length of the injection needle used is not enough (the needle length should be at least 5cm), and the end of the injection needle cannot reach the stator surface. Two. The needle is not completely inserted into the inlet of the needle. Three. Contaminants in the inlet of the injection needle or worn fragments of the injection needle seal will prevent the tip of the injection needle from contacting the stator surface. When inserting or pulling out the injection needle, clean the injection needle or dilute the contaminated sample in this area, and at the same time, the injection needle inlet and sample overflow 5# port are filled with fluid, thus preventing air from entering the sample tube.