Flow-through Bulk Optode for Spectrophotometric Determination of Thiocyanate and Its Application to Water and Saliva Analysis

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/H(2)SO(4)). 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.