Micellar proportion: A parameter to compare the hydrophobicity of the pseudostationary phases or that of the analytes in micellar electrokinetic chromatography

Abstract

Micellar proportion, t(prop,mic) = t(mic)/t(m), a quantity expressing how much time is spent by the analyte in the micellar phase related to its whole migration time (t(m)) has been introduced by utilizing the micellar phase residence time (t(mic)). The t(prop,mic) values have been determined for analytes of different chemical structures (alkyl benzene and alkyl phenone homologous series, alcohols, strongly hydrophobic peptides) studied by micellar elektrokinetic chromatography (MEKC) using various cationic and anionic pseudostationary phases. A good linear correlation was obtained between t(prop,mic) and the calculated hydrophobicity (CLOGP) of the analytes for all pseudostationary phases (CLOGP = A.logt(prop,mic) + B). Considering a given pseudostationary phase, t(prop,mic) as a relative quantity is a suitable parameter to characterize and compare experimentally the behavior of the various analytes in MEKC. Applying a set of probe molecules with known hydrophobicity, the CLOGP(50) value (showing the value of hydrophobicity of a virtual molecule spending exactly 50% of its migration time in the pseudostationary phase) has been calculated for each pseudostationary phase applied here. This experimentally determinable numerical value (characterizing the pseudostationary phase) can be utilized to compare the hydrophobicity and hence retention ability of the pseudostationary phases. The t(prop,mic) value was found to be applicable to compare the methylene selectivity of the different pseudostationary phases as well: logt(prop,mic) = A.Z + B, where Z is the number of carbon atoms of the alkyl chain in the alkyl benzene homologous series.

Characterisation of mixed lithium dodecyl sulphate/lithium perfluorooctanesulphonate pseudo‐stationary phases in MEKC

“…The good linear relationship between the lg t prop;mic and CLOGP values has been proved not only for the single phases [35] but also in the present work in the case of the mixed phases (the R 2 value of the lg t prop;mic and CLOGP curves was better than 0.96 for each mixed phase).…”

“…Applying a set of probe molecules with known hydrophobicity the CLOGP 50 value has been introduced. Low CLOGP 50 represents a highly effective micellar phase to interact with the analyte while for a micellar phase characterised with high value of CLOGP 50 a strong interaction can be expected only for highly hydrophobic analyte [35]. This experimentally determinable numerical value proved to be applicable in comparison of hydrophobicity and hence retention power of different single PSPs.…”

“…Results calculated for the single phases have been presented in [35], and those calculated for the mixed PSPs are summarised here. Detailed experimental parameters can be found in [15,16,35].…”

“…as well as CLOGP 50 value has been calculated as they were defined in [35], (where t m , t mic and Z are the migration time and the micellar phase residence time (time spent by the analyte in the micellar phase) and carbon number of the alkyl chain, respectively).…”

“…Micellar phase residence times have been determined for analytes of different chemical structures (alkylbenzene and alkylphenone homologous series, alcohols, strongly hydrophobic peptides) in different pseudo-stationary single phases (containing only one type of surfactant) by MEKC in our previous work [35]. Micellar proportion (t prop;mic ) has been defined according to Eq.…”