Classification and precautions of the hottest high

Classification and precautions of high performance liquid chromatography injector

in the early stage of high performance liquid chromatography, diaphragm and stop flow injector were used and installed at the inlet of chromatographic column. Now, six way sampling valve or automatic injector are mostly used. Requirements for the sampling device: good sealing, small dead volume, good repeatability, ensuring central sampling, and having little impact on the pressure and flow of the chromatographic system during sampling

classification and precautions for use of high performance liquid chromatography injector

hplc injection methods can be divided into: diaphragm injection, stop flow injection, valve injection and automatic injection

1. Diaphragm injection. Inject the sample into the specially designed injection head connected to the chromatographic column with a micro syringe, and the sample can be directly sent to the center of the column head packed bed. The dead volume is almost equal to zero, which can obtain the best column efficiency, and it is cheap and easy to operate. But it cannot be used under high pressure (such as above 10MPa); In addition, the diaphragm is easy to adsorb the sample to produce memory effect, so that the injection repeatability can only reach 1 ~ 2%; In addition, the rubber that can block various solvents is not easy to find, so the use of conventional analysis is limited

2. Stop flow injection. Injection under high pressure can be avoided. However, in HPLC, due to the pollution of the diaphragm, the "ghost peak" often appears when the pump is stopped or restarted, and the distance between fixtures is 50mm. Another disadvantage is that the retention time is not accurate until the hot joint of the sample is destroyed. In the preparative chromatography in which the beginning and end signals of the peak control the collection of fractions, the effect is better

3. Valve injection. Six way sampling valve is commonly used in general HPLC analysis, and its key components are composed of circular sealing pad (rotor) and fixed base (stator). Due to the dead volume of the valve joint and connecting pipe, the column efficiency is lower than that of the diaphragm injection (about 5 ~ 10% decrease), but it is resistant to high pressure (35 ~ 40MPa), the injection volume is accurate, the repeatability is good (0.5%), and the operation is convenient

there are two kinds of six way valve injection methods: partial liquid filling method and full liquid filling method

① when using the partial filling method for injection, the injection volume should not be greater than 50% (up to 75%) of the volume of the quantitative ring, and the volume of each injection should be accurate and the same. The accuracy and repeatability of this method depend on the proficiency of injector sampling, and it is easy to produce peak broadening caused by injection

② when using the full filling method for injection, the injection volume should not be less than 5 ~ 10 times (at least 3 times) of the volume of the quantitative ring, so as to completely replace the mobile phase in the quantitative ring, eliminate the tube wall effect, and ensure the accuracy and repeatability of injection

rush to the "management position"

precautions for the use and maintenance of the six way valve

① before the sample solution is injected, the hardness of the product must be tested with a 0.45um filter hardness tester, mainly to ensure the quality of the product produced, membrane filtration, so as to reduce the wear of particles on the injection valve

② do not rotate the valve core too slowly, let alone stay in the middle position, otherwise the mobile phase is blocked, causing the pressure in the pump to increase sharply, even exceeding the maximum pressure of the pump; When turning to the injection position, excessive pressure will damage the column head

③ to prevent buffer salt and sample Lu from remaining in the sampling valve, flush the sampling valve after each analysis. Usually, it can be washed with water, or first with a solvent that can dissolve the sample, and then with water

4. Automatic injection. It is used for routine analysis of a large number of samples