SULPHA-DRUG SENSITIVE ELECTRODES: SELECTIVITY AND POTENTIOMETRIC TITRATION

Sulpha-drug sensitive electrodes have been suggested for the potentiometric titration of sulpha-drugs using a standard sulphuric acid solution as titrant with distinct potential jump at the equivalence point and a maximum error of 0.7%. Direct potentiometry is also possible. No significant interferences are caused by commonly met inorganic anions. The selectivity of the electrodes toward different sulpha-drugs has been investigated in detail. It has been found that for all electrodes tested including cetyltrioctylammonium sulphathiazole, sulphadoxine and sulphadimethoxine electrodes, the logK_ij values for the sulpha-drugs can be expressed as a function of molecular connectivity index, pK_a and the electronic charge at the ionizing nitrogen atom of the amide group according to the following equation: logK_ij=ax-b pK_a+cp-d. The correlation has been shown to be significant. However, the correlations between log K_ij and molecular connectivity index, pK., electronic charge either separately or binarily are rather poor.