This article explains how a guard column is one of those HPLC accessories that is a bit of a mixed grill – it can be a good thing or a not-so-good thing. Different aspects of guard column use will be assessed to see if they make sense for you.
The guard column is a miniature column, ideally packed with the same packing material as the analytical column. This is mounted just upstream from the analytical column to protect the analytical column. Guard columns come in a variety of dimensions. For example, on the website for one popular column supplier and for a C18 guard column to go with a 150 x 4.6 mm i.d. column packed with 5-µm particles, they list three different options: 10 x 3.0, 10 x 2.1, and 10 x 1.0 mm i.d, all packed with 5-µm particles. Guard columns inarguably will extend the life of the analytical column. This protection comes in two forms. First, the frits on the guard column are the same as those on the analytical column, so anything that might block the analytical column would block the guard column first, thus protecting the analytical column. On the other hand, guard columns are just one more thing to go wrong in the system. First, you need to figure out how long the guard column will last. If you wait until there is breakthrough of strongly retained material from the guard column to the analytical column, you have waited too long and may damage the analytical column.
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