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

Abstract

A new ion chromatographic (IC) system, which uses zwitterionic (e.g., Zwittergent 3-14) micelles as both stationary and mobile phases, highly useful for the analysis of inorganic anions in biological samples, was developed. The zwitterionic micellar stationary phase (which is obtained by immobilizing the zwitterionic surfactant on surfaces of the reversed-phase ODS) showed high ability to confine the elution bands of the large amount of SO4(2-) and Cl- to narrow zones. As a result, a base-line separation of NO2-, Br- and NO3- from SO4(2-) and Cl- is always achieved. The zwitterionic micellar mobile 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 separation column is therefore always being cleaned up even after the protein-containing sample is directly injected. The zwitterionic micelles are also insensitive to conductivity detection, therefore either the suppressed or the non-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 determination of a number of inorganic anions (SO4(2-), Cl-, NO2-, Br- and NO3-) in both samples have demonstrated the usefulness of this new IC system.

Electrostatic ion chromatography using a carboxybetaine-type zwitterionic surfactant as the stationary phase

“…The coated column was then conditioned with aqueous NaHCO 3 solutions as eluents for the separation of a series of test analytes (NO 2 -, H 2 PO 4 -, Cl -, Br -, NO 3 -, ClO 3 -, I -, and SCN -). NaHCO 3 was chosen as the eluent because it had been found to be applicable for the separation of anions in EIC with sulfobetaine-type zwitterionic as the stationary phase [12], and to enable suppressed conductivity detection to be used [18]. However, when NaHCO 3 eluents were used over the concentration range 1.0-30 mmol L -1 with the EF-700 stationary phase, all of the test analyte anions were unretained.…”

“…Third, EIC provides a simultaneous separation of cations and anions by using a weak/strong-charged zwitterionic surfactant [9] or a sulfobetaine-type zwitterionic surfactant mixed with a sulfonated anionic surfactant [10,11] as the stationary phase and a single electrolyte solution as eluent. The ability to directly determine ions in proteinaceous samples by adding zwitterionic micelles to the eluent [12] is another practical advantage of EIC.…”

Developments in ion chromatography using monolithic columns

“…Pelletier and Lucy [42] reported a 10% decrease in retention after 11 h when using a DDA + coated column with a cyanophenol eluent at 1 mL/min [42]. As mentioned earlier, some researchers have included small amounts of surfactant in the eluent to stabilize the coating [64,67,74]. Reproducible retention can also be achieved by periodically uncoating and recoating the column [48], but this is a time-consuming task which is poorly suited for high throughput and routine analysis.…”

Determination of monovalent inorganic anions in high-ionic-strength samples by electrostatic ion chromatography with suppressed conductometric detection

“…The eluent used in EIC has contained a small amount of the zwitterionic surfactant in order to stabilize the adsorbed layer of zwitterionic micelles comprising the stationary phase [14,15]. This approach has proved particularly suitable for direct spectrophotometric detection of inorganic anions in a range of samples [16][17][18][19][20]. Although suppressed conductometric detection has been applied successfully in EIC [21,22], the inclusion of the surfactant in the eluent has been detrimental to the membrane material of the electric membrane-based self-regenerating suppressor, leading to poor suppression performance and limited lifetime of the suppressor.…”