Characteristics of new composite- and classical potentiometric sensors for the determination of pharmaceutical drugs

The characteristics of new types of coated wire potentiometric sensors based on composite coatings were compared with classical potentiometric sensors. The composite sensors contained respectively the clay montmorillonite (MM) and the zeolite NaY as the ionically conducting components, embedded in PVC based rubber phase membranes. The behavior of 20 basic medicinal drugs and 5 biogenic amines was studied on 9 potentiometric sensors of different composition. The behavior of 3 composite sensors, and 6 more classical PVC based sensors either of the “inner solution” or “coated wire” type were studied. The analytes were chosen to cover a wide log P range of, e.g. −1.54 (noradrenaline) up to +5.55 (promethazine). All sensors were tested using a high-throughput FIA-based method. The results were interpreted via statistical data analysis. The responses of all electrodes had a very high correlation to the log P of the analytes. This was also the case for the ion-pair based electrodes containing a specific cationic drug as the counterion. Classical ion-pair based sensors containing tetrakis (p-chlorophenyl) borate (TCPB) and a counterion with a high log P value (e.g. promazine) were the least sensitive. The composite-based sensors were the most sensitive. Coated wire electrodes were statistically shown to behave in the same way (selectivity and sensitivity) as inner solution electrodes. The results are discussed using a physico-chemical model. Practical applications of the most performant (composite) sensors are shown in HPLC detection of the pharmaceutical drugs and the biogenic amines. Detection limits in the 10−7 M regio (injected concentrations) are obtained for lipophilic drugs (log P > 2).