Precolumn filters are essential for protecting HPLC columns against particulate matter which can accumulate on the column frit, leading to split peaks and high backpressure. Sources of particles include mobile phases (especially when buffers are mixed with organic solvents), leaking pump and injector seals, and samples. Precolumn filters are also useful because changing the column frit is extremely difficult to do without disturbing the column packing, whereas changing the precolumn filter’s frit is easy, providing relatively inexpensive insurance against column damage.