The Role of Chromatographic Guard Column and Precolumn
First of all, we must understand the difference between the guard column and the pre-column. The guard column is generally filled with a filler, which is equivalent to a shortened column. The length is generally about one to two centimeters in length. The column core in the guard column seems to be In front of the open minesweeper, if there is any damage to the column’s contaminants in the mobile phase and the sample, the protection column will be able to withstand it.
The precolumn now generally refers to the prior filter that is close to the injector and the column. The biggest difference between the previous filter and the guard column is that there is no filler, only the replaceable sieve plate, the precolumn can only protect The column is protected from particulate matter and does not block strong-retaining substances dissolved in the mobile phase.
Retention time is a very useful tool for diagnosing separation problems in liquid chromatography. The retention time is influenced by many factors such as the composition of the thin mobile phase, temperature, pH, flow rate, stationary phase loss, and column aging. If all these parameters are kept constant, The retention time also remains constant.
However, in practice, it is impossible to perform perfect control of each chromatographic parameter. For example, even if the column thermostat is added, the temperature will fluctuate; the composition of the mobile phase will change due to the different volatility of the components. Therefore, it is normal for the retention time to have a variation of 0.02-0.05 min above and below, and it is normal for some methods to have a 0.1-min up and down change. There are major changes in retention times, indicating that there are problems with the systems and methods. There are air bubbles in the flow path, there is a leak in the pump valve, and the retention time increases due to the reduced flow rate. Gradient mixing ratio valve failure is also one of the reasons for the retention time change.