Two sizes of Guard Columns are available: 2.0 and 4.0 mm Internal Diameter (ID). Both sizes are 20mm in length and are used with the same Guard Column Holder.
The 2.0mm ID guard columns are for use with the 2.1mm ID Analytical Columns and the 4.0mm ID Guard Columns should be used with the 3.0mm and 4.6mm ID Analytical Columns.
Typically one would use the same Stationary Phase Type in both the Guard and Analytical Columns. However, in some instances it is preferred to use a Reversed Phase Guard Column (such as the Bidentate C18™) with an Aqueous Normal Phase Column (such as the Diamond Hydride™). It depends on which types of Analytes from the matrix one expects to be most problematic in terms of Carryover and Adsorption on the Analytical Column.