Concepción Sánchez-Pedreño

The construction and electrochemical response characteristics of a poly(vinylchloride) (PVC) membrane selective electrode for the determination of tiapride (TPD) are described. The sensing membrane comprised an ion-pair formed between the protonated drug and tetraphenylborate (TPB-) in a plasticized PVC matrix. The influence of membrane composition on the electrode response was studied. The electrode showed a fast, stable and Nernstian response over a wide tiapride concentration range (1x10^-5-1x10^-2 M) with a slope of 57.5±0.2 mV dec^-1 of concentration, a detection limit of 4.3x10^-6±2.5x10^-7 M, a wide working pH range (2-8) and a fast response time (< 5 s). The electrode showed good selectivity towards tiapride with respect to some inorganic and organic compounds. The electrode has been applied to the determination of tiapride in human urine and iontophoresis solution.

A flow-through spectrophotometric bulk optode for the flow-injectiondetermination of thiocyanate is described. As active constituents, the optode incorporatesthe lipophilized pH indicator 5-octadecanoyloxy-2-(4-nitrophenylazo)phenol andmethyltridodecyl ammonium chloride, dissolved in a plasticized poly(vinyl)chloridemembrane entrapped in a cellulose support. The optode is applied, in conjunction with theflow injection technique, to the determination of thiocyanate at pH 7.5 (TRIS/H2SO4). Thesensor is readily regenerated with a 10^-2 M NaOH carrier solution. The analyticalcharacteristics of this optode with respect to thiocyanate response time, dynamicmeasurement range, reproducibility and selectivity are discussed. The proposed FI methodis applied to the determination of thiocyanate in waters from different sources and in humansaliva samples in order to distinguish between smokers and non-smokers.

A flow-through spectrophotometric bulk optode for the flow-injection determination of thiocyanate is described. As active constituents, the optode incorporates the lipophilized pH indicator 5-octadecanoyloxy-2-(4-nitrophenylazo)phenol and methyltridodecyl ammonium chloride, dissolved in a plasticized poly(vinyl)chloride membrane entrapped in a cellulose support. The optode is applied, in conjunction with the flow injection technique, to the determination of thiocyanate at pH 7.5 (TRIS/H2SO4). The sensor is readily regenerated with a 10-2 M NaOH carrier solution. The analytical characteristics of this optode with respect to thiocyanate response time, dynamic measurement range, reproducibility and selectivity are discussed. The proposed FI method is applied to the determination of thiocyanate in waters from different sources and in human saliva samples in order to distinguish between smokers and non-smokers.

An amperometric detector for hydrophobic ions based on a plasticized poly(vinyl) chloride (PVC) membrane incorporated in a flow‐injection system was developed. A four‐electrode potentiostat with ohmic drop compensation was used, while a flow‐through cell incorporated the four electrodes and the membrane, which contained tetrabutylammonium tetraphenylborate. When the influence of the applied potential and of the flow‐injection variables on the determination of tetrabutylammonium was studied, a linear relationship was observed between current peak height and ion concentration over a range of 5×10⁻⁶–6×10⁻⁵ M tetrabutylammonium. Good repeatability and between‐day reproducibility and high sample frequency were obtained. The effect of other ions was studied. Two different amperometric methods, indirect and direct, were also developed for the determination of dodecylsulfate in the concentration range 3×10⁻⁵–9×10⁻⁴ M.

The dynamic potential response of an 18‐crown‐6 based ion‐selective electrode towards Li⁺, Na⁺, K⁺ and Ca²⁺, in a flow‐injection system is studied. Different double nonmonotonic transient signals are obtained for the different ions. The influence of the flow‐injection variables and of ion concentration on the signals is studied. Two signal parameters, the relative return rates, are found to be characteristic for each ion and are constant for a concentration range of 1–3 decades. The nonmomotonic transient signals obtained are explained by reference to the theoretical models reported.