Extended thermodynamic approach to ion interaction chromatography. A mono- and bivariate strategy to model the influence of ionic strength

• Published in: Journal of separation science 2004-11, Vol.27 (15-16), p.1323-1332
• Main Authors: Cecchi, Teresa, Pucciarelli, Filippo, Passamonti, Paolo
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Chemistry; Chromatographic methods and physical methods associated with chromatography; Chromatography - methods; Column liquid chromatography; Dopamine - chemistry; Electrolytes - analysis; Electrolytes - chemistry; Epinephrine - chemistry; Exact sciences and technology; Hydrogen - chemistry; Ion interaction chromatography; Ion interaction reagent concentration; Ionic strength; Ions - chemistry; Models, Chemical; Osmolar Concentration; Other chromatographic methods; Thermodynamic model; Thermodynamics; Tyramine - chemistry
• ISSN: 1615-9306; 1615-9314
• DOI: 10.1002/jssc.200401901

Recent breakthroughs in the theory of ion interaction chromatography (IIC) permit new analyses of the dependence of retention on different interdependent factors. The influence of the ionic strength I on the surface potential, the Donnan effect, and salting effects are taken into account to model the chromatographic behaviour of charged analytes in IIC. The most reliable experimental results found in the literature were used to test the retention equations that were developed following both a monovariate (I changes as the concentration of H, ion interaction reagent, changes) and a bivariate (I changes because of the simultaneous variation of H and of the background electrolyte concentrations) approaches. The present extended thermodynamic model builds on the sound intuition of the electrostatic approach and proves to provide the most successful and exhaustive quantitative explanation of experimental evidence. It is also able to rationalise the less extensive agreement between the pure electrostatic approach predictions and experimental results. The adequacy of the model is supported by physically reliable estimates of the adjustable constant (ion‐pair constants, ΔG°). Moreover statistical practice demonstrates that all the adjustable parameters (three at the most) are statistically significant. A linear, zero crossing function with unit slope is obtained when kpred is plotted against kexp. The mean percent error between kpred and kexp is 4.5% at most. In the absence of H the present retention equation reduces, as expected, to the relationship that describes the influence of I on the retention behaviour in reversed‐phase liquid chromatography.