Columns particle size and

To achieve the optimum reversed-phase LC separation, one needs to explore variables such as the analyte chemistry, mobile-phase composition (solvent type, solvent composition, pH, and additives), column composition, column particle size, and column temperature. For pharmaceutical analysis using mass spectrometry, the chemistry of an analyte is rarely changed beyond manipulation of the mobile phase pH, and even there options are limited. Volatile pH modifiers (buffers) are still preferred for LC-MS, and concentrations of these modifiers are kept low. Relatively simply mobile phases consisting of water, acetonitrile, and either formic acid (0.1% v/v), ammonium acetate (1-20 mM), or both have been common. 

Table 2.8 Columns, particle sizes and their operational conditions.

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