Manipulation of separation selectivity of inorganic anions in electrostatic ion chromatography by the use of mixed cationic-zwitterionic micelles as the column coating solution

This paper describes an electrostatic ion chromatographic system in which t he separation selectivity for inorganic anions, especially for sulfate and phosphate, could be manipulated by altering the molar ratio of the zwitteri onic and cationic surfactants in the column coating solution used to prepar e the stationary phase. The zwitterionic surfactant used for this study was 3-(N,N-dimethyltetradecylammonio)propane (Zwittergent-3-14) and the cation ic surfactant was tetradecyl-trimethylammonium (TTA). Using a reversed-phas e C-18 column (250 x 4.6 mm I.D.) coated with 10/10 (mM/mM) of TTA/Zwitterg ent-3-14 mixed micelles as the stationary phase and either NaHCO3 or Na2CO3 aqueous solution as the eluent, together with suppressed conductivity dete ction, baseline separation of seven model inorganic anions was obtained. Th e elution order for those anions was found to be F-< HPO42- < Cl- < SO42- < NO2- < Br- < NO3-. Under the same conditions but using 1/10 (mM/mM) of TTA /Zwittergent-3-14 mixed micelles as the column coating solution, the elutio n order for these model ions was F- < HPO42- < SO42- < Cl- < NO2- < Br- < N O3-. The early elution of phosphate and sulfate is a unique attribute of th is system. Detection limits for F-, HPO42-, Cl-, SO42-, NO2-, Br- and NO3- (S/N=3, sample injection volume 100 mul) were 0.11, 0.12, 0.12, 0.18, 0.49, 0.49, 0.52 muM, respectively. (C) 2001 Elsevier Science B;V. All rights re served.