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)manganew( Ill) chloride (Mn[TI'I'I'JCI) in a plasticized polyvinyl chloride matrix. The electrode deviates from the tiofmeister selectivity pattern by responding t o 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).It is well known that solvent-polymeric membrane electrodes prepared with conventional dissociated anion exchangers (e.g., tetraalkyl ammonium or similar compounds) exhibit potentiometric anion selectivity patterns in accordance with that predicted by the Hofmeister series [ 11 (i.e,, maximum response to lipophilic anions). Recently, however, various metal-ligand complexes and organometallic species have been used to construct polymeric membrane electrodes that display markedly different anion selectivity sequences 12-12], Metalloporphyrins are one such class of membrane-active molecules that already have proven to be useful in the design of new anion-selective sensors. Previous work has established that differences in potentiometric selectivity can be achieved by changing the metal center [7, 91 and/or altering the peripheral structure of the porphyrin ring [6]. The latter approach is further demonstrated in the present study in which we describe the response ' Present address: