Comparison Techniques For HPLC Column Performance

In the development of a chromatographic method, chromatographers often are required to determine the best column and operating conditions to address the problem at hand. With so many columns and operating conditions to choose from, it is sometimes a challenging task to choose the optimum column parameters (for example, particle size, column length, and column internal diameter) and optimum operating conditions (for example, mobile phase components, buffers, flow rates, and temperature). Often, a given is the high performance liquid chromatography (HPLC) instrumentation at hand, with its maximum pump pressure and flow rate capability and a column that can be installed in the instrument or in the drawer.
For most chromatographers, analyzing HPLC column performance consists of measuring the following four key performance parameters: the column efficiency (H or HETP) (as a function of the mobile phase flow rate), the column permeability, Kv0 (or pressure drop), the retention capacity (k value), and the column selectivity (α) for important pairs of analytes. Whereas the former two essentially are reflecting the packing quality and the mass transfer kinetics of the column, the latter two depend upon the dimensions and the chemistry of the stationary phase (1). Although the overall column quality also is determined by other factors, such as lifetime, chemical inertness, and mass loadability, the present contribution will focus on the first four parameters (H, Kv0, k, and α) because these are of a more general nature than the latter three, which depend strongly upon the chemistry and the economics of the application.