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Extended thermodynamic approach to ion interaction chromatography. Influence of the chain length of the solute ion: a chromatographic method for the determination of ion‐pairing constants
Author(s) -
Cecchi Teresa
Publication year - 2005
Publication title -
journal of separation science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.72
H-Index - 102
eISSN - 1615-9314
pISSN - 1615-9306
DOI - 10.1002/jssc.200401936
Subject(s) - chemistry , lipophilicity , analyte , ion , ion chromatography , chromatography , column chromatography , reagent , chemometrics , bromide , methanol , reversed phase chromatography , analytical chemistry (journal) , inorganic chemistry , high performance liquid chromatography , organic chemistry
The influence of the chain length in Ion Interaction Chromatography (IIC), previously named Ion Pair Chromatography, was investigated. The system examined is a C18 stationary phase and a variable, salt‐controlled, mixture of a phosphate buffer pH 2.1 in methanol containing tetrabutylammonium bromide as Ion Interaction Reagent. IIC proves to be a good alternative to the well established spectrophotometric and conductometric methods of obtaining thermodynamic ion‐pairing constants. The latter increase with increasing analyte chain length and decrease with increasing methanol concentration in the eluent: both results support a physical chemical description of the hydrophobic ion‐pairing process at variance with the classical, Bjerrum‐type modelling of the purely electrostatic interaction between inorganic ions. The calculated Δ G° are reliable because they compare to non‐chromatographic estimates of Δ G° for similar systems. The present extended thermodynamic approach is able to predict and explain why the purely electrostatic approach works better for lower analyte lipophilicity or higher organic modifier concentration.