Ion-exclusion/cation-exchange chromatography (IEC/CEC) on a weakly acidic cation-exchange resin using on acidic eluent,

Ion-exclusion/cation-exchange chromatography (IEC/CEC) on a weakly acidic cation-exchange resin using on acidic eluent, developed by Tanaka et al. in 1994, has been employed to monitor the quality of environmental water samples such as acid rainwater and river water, to analyze body fluid samples such as saliva, and to evaluate water purification by photocatalytic materials.1–8 One advantage of IEC/CEC is the ability to simultaneously separate common inorganic/organic anions and cations in a single run using a simple equipment configuration with just a single column, injection, elution, and detector. In addition, the development of IEC/CEC is ongoing, and analytical performance has been improved for the purpose of analyzing water samples originating from various environments. For example, Mori et al. achieved the high-speed separation of three anions and five cations within 4 min using a separation column packed with a weakly acidic cation-exchange resin with relatively low cation-exchange capacity (0.2 meq/mL) and small particle size (3 μm f) using sulfosalicylic acid as the eluent,6 something that had originally required 30 min. The high-speed analytical method was successfully adapted to a portable-type onsite chromatographic analyzer. Nakatani et al. separated 12 different ions by combining UV detection with postcolumn derivatization for phosphate and silicate ions after conductometric detection (CD).8 The method was successfully applied to the analysis of river water and wastewater samples. Typically, CD is used in conjunction with IEC/CEC, but its analytical sensitivity is quite dependent on the types and the concentrations of acid added to the eluent. When strong acid such as sulfosalicylic acid is used as an eluent, the overall retention time is shortened due to the strong elution power for cation separation by cation exchange. However, the sensitivity for anion separation by ion-exclusion is weaker due to increased conductometric background. In contrast, when weak acid such as phthalic acid is used, the conductometric background is reduced, and the sensitivity for anion separation is improved. However, the lower background levels reduce the sensitivity for cation detection in the negative direction. Therefore, using CD in conjunction with IEC/CEC requires the optimization of the eluent and consideration of the sensitivity needed for both anions and cations. Surprisingly, the use of IEC/CEC with detection methods other than CD have not been reported, except for direct 2013 © The Japan Society for Analytical Chemistry