Ion-exclusion/cation-exchange chromatographic determination of common inorganic ions in human saliva by using an eluent containing zwitterionic surfactant

Ion-exclusion/cation-exchange chromatography with an eluent containing the bile salt-type zwitterionic surfactant CHAPS was performed in order to evaluate variations in anion (SO42−, NO3−, and SCN−) and cation (Na+, K+, NH4+, Mg2+, and Ca2+) concentrations in human saliva. CHAPS prevents the adsorption of proteins to the stationary phase, i.e., weakly acidic cation-exchange resin, since it aggregates proteins without denaturing them. Addition of 1 mM CHAPS to the eluent comprising 6 mM tartaric acid and 7 mM 18-crown-6 yielded reproducible separations of anions and cations in protein-containing saliva. The resolutions of anions and cations were not significantly affected by the addition of CHAPS to the eluent. The concentrations of Na+ and K+ varied before and after meals; or that of SCN−, upon smoking. The relative standard deviations of peak areas ranged from 0.3 to 5.1% in 1 day (n = 20) and from 1.4 to 5.8% over 6 days (n = 6).