CALCULATION OF MODIFIED CAPACITY FACTOR IN MICELLAR ELECTROKINETIC CHROMATOGRAPHY

In addition to the expression, k' = (t(m)-t(o))/t(o) (1-t(m)/t(mc)), w e propose the expression k'' = (t(m)-t(o))/(t(mc)-t(o)) to calculate t he capacity factor in micellar electrokinetic chromatography (MEKC), w here t(m), t(o), and t(mc) are the migration time of the analyte, the flow marker, and the micelles, respectively. The k' and k'' values tha t were obtained from simulated data as well as from MEKC analysis of d ifferent peptides (in 100 mM sodium dodecyl sulfate/0.1 N sodium berat e buffer at pH 11.0) were calculated and compared. The k' value is equ al to zero for an analyte remaining in the aqueous phase whereas it is equal to one for an analyte always staying in the micellar phase. By applying k'' a finite capacity factor can be obtained for an analyte, indicating its partition between the two moving phases (aqueous and mi cellar) even in those cases when t(m) equals t(mc). The slope of the c urve k'' as a function of t(m) is constant through the whole migration window and therefore peak compression does not occur when applying k' ' to calculate the capacity factor. A given difference in k'' correspo nds the same difference in migration times and this value does not dep end on the position within the migration window. Since k' is a normali zed parameter it is easy to evaluate the significance of a given diffe rence in capacity factor or to estimate the relative position of an an alyte with a given capacity factor in the migration window by applying k''. Therefore, k'' seems to be an adequate parameter to calculate th e capacity factor in MEKC and, similar to k', it also refers to the hy drophobicity of the analyte.