Until recently, the use of small particles (i.e.less than 3μm in diameter) was not practical because of the pressure limitations of commercially available HPLC pumps.With multiple ultra high pressure systems now available, columns packed with small particles are generating a significant amount of interest.According to the van Deemter Equation, which relates flow rate to column efficiency, when particle size is decreased large gains in efficiency can theoretically be achieved.Additionally, a flatter efficiency profile allows for a wider range of flow rates without significant loss of resolution.