Substantiation of the Selection of Trifluoroacetophenone Derivatives for the Manufacture of Membranes of Sulfate- and Carbonate-Selective Electrodes

Resumo

The distribution of trifluoroacetophenone (TFAP) and its derivatives—p-methyl trifluoroacetophenone (p-MTFAP), 2,4-dimethyl trifluoroacetophenone (DMTFAP), 2,4,6-trimethyl trifluoroacetophenone (TMTFAP), and heptyl p-trifluoroacetylbenzoate (H-p-TFAB)—in a hexane–water system, which simplifies a polyvinylchloride membrane of selective electrodes, is studied by UV spectrophotometry and chromatography. These substances are used as neutral carriers (NCs) in membranes of ion-selective electrodes reversible to doubly charged carbonate and sulfate ions. The hydration of TFAP and some of its derivatives is systematically investigated. It is found that TFAP has higher solubility in water (partition coefficient D = 415) compared to those of p-MTFAP, DMTFAP, TMTFAP, and H-p-TFAB (D = 1360–2700), which makes it unsuitable as a neutral carrier for manufacturing membrane electrodes. H-p-TFAB is most strongly hydrated in an alkaline medium. It is found that p-MTFAP and H-p-TFAB form crystalline hydrates. The selectivity coefficients for the carbonate- and sulfate-selective electrodes are determined for all the neutral carriers studied; the selectivity of the electrodes increases in the series TFAP < p-MTFAP < DMTFAP < TMTFAP < p-BTFAP (p-butyl trifluoroacetophenone) < H-p-TFAB.