Mn(III)-porphyrin-based thiocyanate-selective membrane electrodes: Characterization and application in flow injection determination of thiocyanate in saliva

The response properties of a new thiocyanate‐selective solvent‐polymeric membrane electrode are reported. The membrane contains (5,10,15,20‐tetrakis(2,4,6‐triphenylphenyl)porphyrinato)manganese(III) chloride (Mn[TPPP]CI) in a plasticized polyvinyl chloride matrix. The electrode deviates from the Hofmeister selectivity pattern by responding to thiocyanate preferentially over inorganic anions (perchlorate, chloride, iodide, and bromide) and several organic anions often present in biological samples (ascorbate, citrate, urate, and salicylate). The performance of this electrode as an ion‐selective detector in a low‐dispersion, flow‐injection system is also evaluated. While selectivity in such a nonequilibrium flow arrangement is found to be somewhat different than that observed under equilibrium conditions, the electrode's response and selectivity is still adequate to allow for measurement of thiocyanate in biological samples. This application is demonstrated via the flow‐injection analysis (FIA) detection of thiocyanate in 22 human saliva samples with good correlation to a classical colorimetric method (r = 0.981).