Steps for Ensuring Good Column Performance

Step 3:  Know When to Use and Change a Guard Column

The main purpose of the guard column is to act as a trap for highly retained sample components and for particulate matter. It is installed after the injector and before the analytical column. Protecting your analytical column by using guard columns can substantially increase column lifetime. But it is important to know when to change the guard column for the best protection of the analytical column. To be effective the guard column must be replaced often enough to prevent contaminants from reaching the analytical column.

Monitoring Chromatographic Parameters:
A "quantitative" way of knowing when to replace a guard column
The best way to determine the right time to replace a guard column for a specific set of sample and mobile phase conditions is through experience. However it is valuable to have some quantitative measure to help make the replacement decision. By monitoring plate number (N), pressure (P), and resolution (Rs), the performance of the guard and the analytical column, can be closely watched to determine when a guard column should be replaced.

IMPORTANT NOTE:
Even though monitoring N, P, and R_s provides clues as to when guard columns should be replaced, you cannot always be certain if the guard column is adequately protecting the analytical column. Fouling of the analytical column can still take place (due to a saturated guard column) before a 10% change in N, P, or R_s is observed. It is always better to replace the guard column too soon rather than too late.

In the absence of other information, a good rule-of-thumb is to replace the guard column after every 150 sample injections or 1,000 analytical column volumes of mobile phase, whichever is reached sooner.

Table of Contents  | Section 2  |  Step 1  |   Step 2  |  Step 4  

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