High performance liquid chromatography (HPLC) is a separation technique used in many areas of analytical chemistry to separate, identify and qualify various compounds in a specific solution. HPLC uses a column that holds chromatographic packing material that retains molecules as they are pumped through the column, the retention time being dependent on the packing material, the carrier liquid (solvent) and the specific type of molecule. Each chemical species in the injected sample is most commonly identified by UV and mass spec detection.
Most traditional analytical HPLC packing materials have an average diameter of approximately 2 to 30 microns and are typically silica-based or alumina-based. The particle size of the packing material is usually measured using methods that assume all particles are uniformly spherical. But, this may not be the case, as in the manufacture of silica and bonding, where fines and irregularly shaped particles can be a percentage of the final product. As particle size decreases, the effect of fines and irregularly shaped particles demands a greater degree of control on incoming quality of the silica material. Variation in particle shape can directly affect reproducible performance. Filling stage backpressure of the column can vary greatly depending on the shape of the HPLC particles.