How to Select Guard Column Correctly?

      How to select guard column which does not affect segregation analysis? In general, whether the sample is clean should firstly be considered before choosing the guard column. For a majority of analysis personnel, a 1cm long guard column is enough to provide adequate protection. However, if the sample is very dirty, or the 1cm long guard column has to be replaced frequently at work, the 2cm or 3cm long guard column should be selected. The longer the guard column is, the more the chromatographic packing will be and the better protection performance it will offer. Certainly, with the increase of guard column length, the sample’s retention time will also increase. Generally speaking, it is appropriate that the internal diameter of the guard column is the same or equivalent to that of the analysis chromatographic column. The packing filling method of guard column is also very important. There is a type of guard column which is filled in membrane method. With simple and convenient use process, it can be dry loaded in the laboratory. However, its biggest drawback is diseconomy: especially under China's specific conditions, one-time use cost is relatively high. In addition, the guard column filled in membrane method has a limited amount of chromatographic packing, which can only provide very limited protection; however, as there is a small amount of chromatographic packing, the guard column has short length, which will bring small impact to the retention time of sample analysis. Another type of guard column has actually shortened the chromatographic analytical column. It has the designs of direct-coupled/hand tightened or integral type. The integral type design: The guard column has been directly installed on the chromatographic analytical column by the manufacturer, and must be ordered along with the chromatographic analytical column; it can be used conveniently but cannot be modified. The direct-coupled type design: The guard column can be installed or connected by chromatographic personnel at any time; it can be used with any brand of chromatographic column; guard columns of proper length can be selected according to different samples. Hand tightened type design: The guard column of this design is the same as the direct-coupled type guard column in terms of structure; instead of using a wrench, it can be tightened by hand. In addition, from the perspective of guard column structure, guard columns can be divided into the ones with replaceable column cores and the ones with irreplaceable column cores. At present, most guard columns have replaceable column cores, which may reduce the use cost of guard columns. Most people select packing for guard columns according to the packing of chromatographic analytical column. Under normal circumstances, you may choose the same chromatographic packing for chromatographic analytical column. However, in actual analysis, the packing for guard columns is unnecessarily the same as that for chromatographic analytical column. The principles to select guard columns are as follows: In the premise of meeting segregation analysis requirement, select short guard columns as far as possible and select packing with smaller retention on samples which await separation as far as possible.