Determination of inorganic anions in biological fluids with direct sample injection by electrostatic ion chromatography using zwitterionic micelles in both stationary and mobile phases

A new ion chromatographic (IC) system, which uses zwitterionic (e.g., Zwitt ergent 3-14) micelles as both stationary and mobile phases, highly useful f or the analysis of inorganic anions in biological samples, was developed. T he zwitterionic micellar stationary phase (which is obtained by immobilizin g the zwitterionic surfactant on surfaces of the reversed-phase ODS) showed high ability to confine the elution bands of the large amount of SO42- and Cl- to narrow zones. As a result, a base-line separation of NO2-, Br- and NO3- from SO42- and Cl- is always achieved. The zwitterionic micellar mobil e phase, (which is obtained by dissolving the zwitterionic surfactant with a suppressive electrolytic solution, e.g., aqueous NaHCO3 solution), on the other hand, showed high ability for rapid elution of proteins. The separat ion column is therefore always being cleaned up even after the protein-cont aining sample is directly injected. The zwitterionic micelles are also inse nsitive to conductivity detection, therefore either the suppressed or the n on-suppressed conductivity detection method is applicable for detection of the analyte ions. Urine and serum were chosen as the model real samples and were analysed with direct sample injection; the results of successful dete rmination of a number of inorganic anions (SO42-, Cl-, NO2-, Br- and NO3-) in both samples have demonstrated the usefulness of this new IC system.