ABSTRACT
Placing a small column in front of a more expensive analytical or preparative column to prolong its usefulness has become popular in high-performance liquid chromatography. Guard devices can be thought of as more-or-less expendable columns designed to remove anything that will interfere with the separation or shorten the lifetime of the primary column. Off-line columns sometimes referred to as clean-up columns, can remove all of the categories; however, they can add time to the analysis and cause sample loss and sample dilution. On-line methods require high-pressure, stainless steel column designs. The dimension of the guard column and type of packing combine to determine overall performance. Due to its location at the column system inlet, a guard device sees the impact of high pressure and high sample concentration so it must be changed regularly. The principles of selection and testing remain the same regardless of column inner diameter and flow rate.
