Micellar electrokinetic capillary chromatography theory based on conventional chromatography

From the definitions of retention time (tR) and resolution (Rs) in conventional chromatography, two fundamental equations for the retention behaviour and resolution of neutral solutes are derived and proved to be valid in all cases of micellar electrokinetic capillary chromatography (MECC). Two parameters, phase velocity ratio (Pr) and column availability (Aco), are introduced to reveal clearly the relationships and differences between MECC and conventional chromatography. The tR and Rs values may be either positive or negative in MECC. A negative tR indicates that the solute migrates toward the positive electrode and a positive tR toward the negative electrode. Rs > 0 means that the solute with a smaller value of the capacity factor (k') in the pair of solutes reaches the detector first, while Rs < 0 means that the elution order is the opposite. MECC can be classified into eight cases depending on the values of Pr for convenience of discussion. So far, MECC was usually performed in case IV and the resolution was poorer than that in conventional chromatography for given values of theoretical plate number, selectivity and k'. However, a better resolution can be obtained in cases II, VI and VIII when Pr < (1-k')/2. Cases VI, VIII and II are preferable to case IV for high resolution and should be more frequently employed in the future.