A guard column can be useful if the injection sample consists of a complex matrix with partially unknown content. However, a guard column does never make sample filtration redundant! If a guard column is to provide adequate protection for the analytical column, it must be changed often enough in order to avoid the column performance from deteriorating. By monitoring plate number (N), pressure, and resolution (Rs), the performance of the guard column, as well as the analytical column, can be assessed and a suitable moment for exchanging the guard column can be chosen.
As a rule of thumb, the guard column should be replaced when one of the following points applies:
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