Selection of Guard Column, How to Choose Liquid Chromatography Guard Column
How to choose a guard column without affecting the separation analysis? Often, the first thing to consider before choosing a guard column is whether the sample is clean. For most analysts, a 1 cm long guard column provides adequate protection. However, if the sample is very unclean, or if it is found to be frequently replaced with a 1cm guard column, then a 2cm or 3cm guard column should be used. The longer the guard column, the more chromatographic packing is naturally loaded, the more protective it is. Well, of course, as the length of the guard column increases, the retention time of the sample increases accordingly. Generally, the inner diameter of the guard column is the same as or equal to the inner diameter of the analytical column.
The packing method of the guard column is also very important. At present, there is a film packing method protection column, which is simple and convenient to use, and can be dry-packed in a laboratory. However, its biggest drawback is that it is uneconomical, especially for the specific situation in China, and the relative cost of one-time use is relatively high. In addition, the membrane packing method has a limited packing of chromatographic packing and can only provide very limited protection; however, because of the small amount of chromatographic packing loaded and the length of the guard column is short, the retention time of the analytical sample is The impact is also small.
Another type of guard column structure is the shortened chromatographic column, which is designed to be directly connected/hand-tight or monolithic. The monolithic design is installed directly on the chromatographic column by the manufacturer of the column and must be ordered with the chromatographic column. It can be used very conveniently, but cannot be modified. The direct-connected design allows the chromatographer to be installed at any time, can be used with any brand of column, and can choose the appropriate guard column length for different samples. The hand-tight guard column is structurally the same as the direct-connected guard column, but can be directly tightened by hand without the use of a wrench or the like when connecting. In addition, from the perspective of the structure of the guard column, the structure of the guard column is further divided into whether the pillar of the guard column can be replaced. Now, most of the guard columns can be replaced with the core, which can reduce the use cost of the guard column.
Most people choose the packing to protect the column based on the packing of the chromatographic column. Normally, the same chromatographic packing as the analytical column can be selected. However, depending on the actual analytical work, it is not necessary to fully match the packing of the analytical column.
The principle for selecting a guard column is to select a shorter guard column as much as possible while satisfying the requirements of the separation analysis, and to select as much as possible a small retaining filler for the separated sample.