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Influence of electrolyte nature on the separation selectivity of amphetamines in nonaqueous capillary electrophoresis: Protonation degree versus ion pairing effects
Author(s) -
Descroix Stéphanie,
Varenne Anne,
Geiser Laurent,
Cherkaoui Samir,
Veuthey JeanLuc,
Gareil Pierre
Publication year - 2003
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/elps.200305372
Subject(s) - chemistry , electrolyte , capillary electrophoresis , ionic strength , ion , acetonitrile , solvent , selectivity , protonation , ionic bonding , dilution , electrophoresis , formate , inorganic chemistry , analytical chemistry (journal) , chromatography , organic chemistry , aqueous solution , thermodynamics , electrode , physics , catalysis
The simultaneous analysis of Ecstasy and its derivatives in an acetonitrile‐methanol (80:20 v/v) mixture was previously shown to be strongly dependent on the nature of the electrolyte (acetate versus formate). To elucidate the phenomena involved, systematic experiments were conducted in this solvent medium. Conductivity measurements allowed to evaluate the ion‐pairing rate in the background electrolyte (BGE) and thereby distinguish between electrolyte concentration and ionic strength. The influence of electrolyte concentration on analyte effective mobilities (μ eff ) was studied by capillary electrophoresis (CE). As μ eff extrapolated to infinite dilution proved to be independent of the nature of the electrolyte, selectivity changes could not be attributed to a modification in the protonation degree of amphetamines. Experimental mobility data were then confronted to existing theoretical mobility models to discriminate between ion pairing or simple ionic strength effect. Ion‐pair formation in a BGE containing acetate was highlighted with an ion‐pairing model and ion‐pair formation constants between each amphetamine and acetate ion were calculated.