Evaluation of an ODS Column Modified with Zwitterionic/Nonionic Mixed Surfactants and Its Application to Direct Injection Determination of Inorganic Anions

• Published in: Analytical Sciences 2005, Vol.21(8), pp.913-916
• Main Authors: HASEGAWA, Takuya, UMEMURA, Tomonari, KOIDE, Akira, CHIBA, Koichi, UEKI, Yuji, TSUNODA, Kin-ichi, HARAGUCHI, Hiroki
• Format: Article
• Language: English
• Subjects: Anions - analysis; Anions - chemistry; Chromatography - instrumentation; Chromatography - methods; Silicon Dioxide - chemistry; Surface-Active Agents - chemistry
• ISSN: 0910-6340; 1348-2246
• DOI: 10.2116/analsci.21.913

An octadecylsilica (ODS) column modified with zwitterionic/nonionic mixed surfactants was evaluated for the direct injection determination of inorganic anions in biological fluids by ion chromatography. A zwitterionic surfactant (sulfobetaine-type) and a nonionic surfactant (polyoxyethylene-type) were used for a stationary-phase modification. When aqueous electrolyte solutions with concentrations of sub-mM to several mM were used as a mobile phase, the zwitterionic surfactant coated on the ODS surface exhibited unique separation selectivity for ionic species, while the nonionic surfactant coated on the ODS might have formed a hydrophilic network over the ODS surface and restricted matrix proteins from adsorbing on the stationary phase. Consequently, the mixed surfactant-modified column system allowed an efficient ion chromatographic separation of inorganic anions as well as a size-exclusive removal of column-fouling proteins. This separation system was applied to the direct injection determination of UV-absorbing anions in human saliva. The detection limits for nitrite, nitrate, iodide and thiocyanate were 3.1, 2.7, 4.5 and 25 µM, respectively, with UV detection at 210 nm (injection volume; 20 µl), and their relative standard deviations for 5 replicate measurements of saliva samples spiked with 100 µM each of those anions were 1.4, 0.9, 2.2 and 5.5%, respectively.