Determination of association constants of inorganic ions with C-12- and C-14-alkyldimethylammoniopropane sulfonate zwitterionic surfactants using capillary electrochromatography

Association constants (K-ass) of 10 inorganic anions (chloride, bromide, io dide, nitrite, nitrate, chlorate, thiocyanate, iodate, perchlorate, and mol ybdate) and seven inorganic cations (lithium, sodium, potassium, rubidium, caesium, magnesium, and cerium(III)) with micelles of two zwitterionic surf actants 3-(N,N-dimethyldodecylammonio)propane sulfonate (C12N3S) and 3-(N,N -dimethylmyristylammonio)propane sulfonate (C14N3S) were determined using c apillary electrochromatography (CEC). These K-ass values of anions with C12 N3S increased as follows: Cl- (4.2 +/-0.1) < IO3- (4.6 +/-0.1) < Br- (5.9<p lus/minus>0.1) < NO2- (6.2 +/- 0.1) < MoO42- (7.8 +/- 0.1) < NO3- (14 +/- 1 ) < ClO3- (26 +/- 1) < I- (68 <plus/minus> 7) < SCN- (310 <plus/minus> 30) < ClO4- (800 +/- 200) dm(3) mol(-1). Similar K-ass values were obtained for C14N3S micelles, but K-ass values of these anions with a non-ionic surfact ant and with a non-surfactant-type zwitterion (used for comparative purpose s) were small. The Kris values of cations with the C12N3S micelle in 10 mM imidazole-20 mM 2-morpholinoethanesulfonic acid (MES) buffer of pH 6.2 incr eased as follows: Rb+ (1.4 +/- 0.1) = Cs+ (1.4 +/- 0.1) = K+ (1.4 +/- 0.1) < Na+ (3.2 <plus/minus> 0.1) < Li+ (4.5 <plus/minus> 0.1) < Mg2+ (7.8 <plus /minus> 0.1) < Ce3+ (12 <plus/minus> 1) dm(3) mol(-1). The fact that the K- ass values for polarisable anions, such as iodide and thiocyanate, were lar ger than those of cations of +2 and +3 charge, agrees well with the relativ e retentions for those ions in electrostatic ion chromatography (EIC). (C) 2001 Elsevier Science B.V. All rights reserved.