Samples may contain precipitates or other contaminates such as metal compounds which bind with the resin. Contaminates change the column chemistry, resulting in a decrease in the effective surface area of the column and decreasing sample retention. Pre-filter all samples through a 0.45 μm or smaller filter membrane prior to injection. Compounds which may bind irreversibly with the resins should be removed using solid phase extraction (SPE) procedures.To provide maximum protection for the analytical column, Benson Polymeric recommends the use of our pre-column (guard).