Rm. Seifar et al., MECHANISM OF ELECTROKINETIC SEPARATIONS OF HYDROPHOBIC COMPOUNDS WITHSODIUM DODECYL-SULFATE IN ACETONITRILE-WATER MIXTURES, Analytical chemistry, 69(14), 1997, pp. 2772-2778
The effect of the addition of 0-70% (v/v) acetonitrile (AcCN) as organ
ic modifier, into a buffer solution containing 0-60 mmol L-1 sodium do
decyl sulfate (SDS), ion the electrokinetic behavior of neutral hydrop
hobic compounds has been studied experimentally. The effective mobilit
ies of the hydrophobic compounds sharply decreased above a certain AcC
N concentration, depending to some extent on the SDS concentration, In
solutions with up to 40% AcCN, with SDS concentrations below the lite
rature values of the critical micelle concentration, neutral hydrophob
ic analytes still showed a considerable electrophoretic mobility; The
observed mobilities were too high to be attributed to solvophobic inte
raction of the analytes with single SDS ions, From conductivity measur
ements, a strong indication was found that increasing the fraction of
AcCN in the SDS solution does not lead to a complete disintegration of
the micelles. Even with high AcCN concentrations, the mechanism of th
e separation was found to be a distribution between the aqueous phase
and micelle-like SDS aggregates. The influence of the addition of AcCN
on the mobilities could be explained as the combined effect of a decr
ease of the micellar volume fraction, a change of the micellar propert
ies, acid a decrease of the distribution constants of the analytes.