How to judge when the chromatographic column should be repla

Chromatographic workers often encounter such problems. When should the chromatographic column be replaced? Can the number of plates of chromatographic column reflect the state of chromatographic column? Determine the standard indicating that the column should be "retired". From experience, when the number of plates of a column is reduced to what percentage of a new column, it can be considered that the column can no longer be used. How do you judge that the column can not be reused in your laboratory?
It is believed that every chromatographic worker will be concerned about the resolution, which is an index to evaluate the quality of root column separation of specific samples. The core task of chromatography is to make each peak complete separation. In practice, we need to get a narrow peak with reasonable peak width in order to obtain a lower detection limit (this is not a difficult problem, the current chromatographic column can meet this requirement).
A better method is to use the mixed index of pressure, resolution and peak shape to investigate the state of root column. It is easy to measure the pressure. Generally, the chromatographic method we determine should meet the following requirements: when using a new column, the column pressure should not be less than 2500 psi, and in any case, the pressure should not exceed 3000 psi. Although modern liquid chromatography systems can be used at higher pressures, the problems of system loss and leakage caused by pressure can be very serious. When the pressure exceeds 3000 psi, consider replacing the on-line filter with a diameter of 0.5 mm between the injector and the column. If the pressure remains after the filter is replaced, the filter or column of the chromatographic column has been contaminated, which indicates that we should replace the column. Statistics show that more than 60% of the chromatographic column damage is due to overpressure.
The resolution is a very important index for us to investigate the chromatographic column. As long as the baseline separation can be obtained for the two components, there will be no problem for the quantification of the analyte. For symmetrical peaks, baseline separation can be achieved at a resolution of 1.5, and better if RS is between 1.7 and 2.0. If the tailing is serious, a higher resolution is needed. The advantage of using resolution as the evaluation index of chromatographic column is that we can directly see the separation of adjacent peaks.
The other standard to inspect the quality of chromatographic column is the tailing of the peak shape. The peak shape of the factory test report is very beautiful, but this does not represent the actual sample analysis of the chromatographic column. The actual samples always contain more or less components that cause the tailing of peaks. It is worth mentioning that compounds containing nitrogen atoms are closely bound to the free silicon hydroxyl groups on the silica gel skeleton. With the longer the chromatographic column is used, the bond phase will be lost and the tailing will be more serious. However, the change in tailing is not as immediately visible as a change in resolution. Based on this, the upper limit of a tailing factor should be determined. For example, the United States Pharmacopoeia stipulates that the tailing factor should not exceed 1.8.
The time to determine the "discard" standard of chromatographic column is when we develop analytical methods or conduct method certification. Usually, in the process of developing analytical methods, you test several columns to analyze enough actual samples, and you know what happens when the separation becomes poor. I tend to start with a wide range. Our experience is this: if you tighten the system applicability requirements at the beginning, it will be difficult to relax the requirements after the method certification. Before analyzing the actual sample, the applicability of the system should be inspected to ensure that the chromatographic method meets the standards acceptable to the analyst.
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