Dionium Cations as Novel Sensing and Separation Reagents for Phthalates in Ion-Selective Electrode Method and in Ion-Pair Chromatography

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An ion selective electrode was prepared which exhibited selectivity for terephthalate over various interfering anions including phthalate under alkaline conditions; a dionium cation, decamethylenebis(trioctylphosphonium) (abbreviated as C₁₀BP), was used as the sensing material. Ion selective electrodes based on conventional monoonium cations such as "Capriquat" did not exhibit such selectivity. The butyl analogs of C_nBPs were examined as ion-pair reagents in ion-pair chromatography for phthalates. Under alkaline elution conditions, the base-line separation of three phthalate isomers (phthalate, isophthalate and terephthalate) was achieved. When monoonium reagents such as tetrabutyl-ammonium were used, the retentions of these isomers considerably decreased, compared to the case of dionium reagents, and the separation could not be attained. The superiority of the dionium cations in both the sensing and separation systems was discussed.