Ion-interaction chromatography

In reversed-phase HPLC with water/organic eluents, ionic interactions always play an important role in regard to analyte retention, solvation, ionic equilibria, and other processes. To some extent, chromatographic effects and practical use of ionic interactions have been discussed in the previous sections of this chapter. In this section the influence of the ionic additives in the mobile phase on the retention of ionic or ionizable analytes will be discussed. 

Ion-interaction chromatography is an intermediate between reversed-phase and ion-exchange chromatography. Introduction of amphiphilic and Uo-philic ions into the mobile phase causes their adsorption on the hydrophobic surface of packing material with subsequent transformation into a pseudo ion-exchange surface. Ionic interactions with charged analytes can occur in the mobile phase and with counterions that may be adsorbed on the stationary-phase surface. 

Specific effect of amphiphilic ions on the retention of charged analytes was observed by many researchers more than three decades ago [112-115]. 

Remarkable number of different names was introduced to these methods. The technique has been called soap chromatography [113], solventgenerated ion-exchange [114], ion-interaction [115], and ion-pair [116]. Researchers introduced a similar number of different theories for the description of the effect of ionic mobile-phase additives on the retention of charged analytes essentially, each specific name for this technique corresponds to its own distinct retention theory. Melander and Horvath [116] divided existing theories into two main groups stoichiometric [113,114,117-119] and nonsto-ichiometric [120-133]. 

Phenomenologically, two different mechanisms could be envisioned (a) the formation of the ion pair between the analyte and amphiphilic counterion with subsequent adsorption of this complex on the stationary phase and (b) adsorption of the amphiphilic counterion itself on the stationary phase surface and subsequent retention of charged analyte in essentially an ion-exchange mode. Melander and Horvath [117] concluded that, in reality, probably both mechanisms coexist in the chromatographic system. 

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Janos, P., Separation of some metals as their anionic oxalate complexes by reversed-phase ion-interaction chromatography, /. Chromatogr., 635, 257,1993. 

A thermodynamic approach has also been employed on ion interaction chromatography (IIC) to predict the retention of neutral and ionic analyte species. The basic equations describing retention are... 

T. Cecchi, Extended thermodynamic approach to ion interaction chromatography a thorough comparison with the electrostatic approach, and further quantitative validation. J. Chromatogr.A 958 (2002) 51-58. 

An overview and discussion is given of literature methods published after 1989 devoted to the ion-interaction chromatographic determination of inorganic anions. Seventy references are quoted. Ion-interaction chromatography makes use of commercial reversed-phase stationary phase and conventional high-performance liquid chromatography instrumentation. The basis of the technique, the modification of the stationary phase surface, the choice of the ion-interaction reagent as well as the dependence of retention on the different variables involved are discussed. Examples of application in the fields of environmental, clinical and food chemistry are presented. The experimental conditions of stationary phase, of mobile phase composition as well as detection mode, detection limit and application are also summarized in tables. 1997 Elsevier Science B.V. 

Keywords Reviews Ion-interaction chromatography Inorganic anions... 

This review is devoted to the ion-interaction chromatographic determination of inorganic anions. Ion-interaction chromatography is a powerful tech-... 

Separation of rare earths by dynamic coating ion-interaction chromatography. 68... 

Cecchi, T., PucciareUi, F., and Passamonti, P. Extended thermodynamic approach to ion interaction chromatography influence of the organic modifier concentration. Chromatographia 2003, 58, 411-419. 

Iskandarani, Z. and Pietrzyk, D. J. Ion interaction chromatography of organic anions in the presence of tetraaUcylammonium salts. Anal. Chem. 1982, 54,1065-1071. 

Xianren, Q. and Baeyens, W. Retention and separation of inorganic anions by reversed-phase ion-interaction chromatography on octadecyl silica. J. Chwmatogr. 1988, 456, 267-285. 

Bidlingmeyer, B.A. Separation of ionic compounds by reversed-phase liquid chromatography an update of ion-pairing techniques. J. Chmmatogr. 1980,18, 525-539. Sarzanini, C. et al.. Retention model for anionic, neutral and cationic analytes in reversed-phase ion interaction chromatography. AnaL Chem. 1996, 68,4494-4500. 

Zou, J., Motomi, S., and Fukutomi, H. Reversed-phase ion-interaction chromatography of inorganic anions with tetraaUcylammonium ions and divalent organic anions using... 

Cecchi, T., Pucciarelli, R, and Passamonti, P. Ion interaction chromatography of neutral molecules. Chromatographia 2000, 53, 27-34. 

Cecchi, T. et al. Chromatographia The dipole approach to ion interaction chromatography of zwitterions. Chromatographia 2001, 54,38-44. 

Cecchi, T. et al. The fractional charge approach in ion-interaction chromatography of zwitterions influence of the stationary phase concentration of the ion interaction reagent and pH. J. Liq. Chromatogr. Rel. Technol. 2005, 28, 2655-2667. 

Cecchi, T. Comprehensive thermodynamic approach to ion interaction chromatography. In Dekker Encyclopedia of Chromatography. Cazes, J., Ed., Marcel Dekker New York,... 

Zappoli, S. and Bottura, C. Interpretation of the retention mechanism of transition metal cations in ion interaction chromatography. Anal. Chem. 1994, 66, 3492-3499. 

Sacchero, G. et al. Comparison of prediction power between theoretical and neural-network models in ion-interaction chromatography. J. Chromatogr. A. 1998, 799, 35-45. 

Okamoto, T., Isozaki, A., and Nagashima, H. Studies on elution conditions for the determination of anions by suppressed ion interaction chromatography using a graphitized carbon column. /. Chromatogr. A. 1998, 800, 239-245. 

Connolly, D. and Pauli, B. Rapid detemination of nitrite and nitrate in drinking water samples using ion-interaction chromatography. Anal. Chim. Acta 2001, 441, 53-62. 

Zappoli, S., Morselh, L., and Osti, F. Apphcation of ion interaction chromatography to the determination of metal ions in natural water samples. J. Chromatogr. A. 1996,721, 269-277. 

Sivaraman, N. et al. Separation of lanthanides using ion-interaction chromatography with HDEHP coated columns. J. Radioanal. Nucl. Chem. 2002, 252, 491-495. 

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