FLOW-INJECTION AMPEROMETRIC DETERMINATION OF THIOCYANATE AND SELENOCYANATE AT A COBALT PHTHALOCYANINE MODIFIED CARBON-PASTE ELECTRODE

Inorganic anions containing sulfur (SO32-, S2O3-, and SCN-), selenium (SeO32- and SeCN-), nitrogen (NO2-), and arsenic (AsO2-) oxidize readily at a carbon paste electrode (CPE) modified with cobalt phthalocyanine (CoPC-CPE). All of these anions are virtually non electroactive (with the exception of SeCN-) towards the CPE. The CoPC-CPE was used as an amperometric flow sensor for the direct determination of SCN- and SeCN-. The application of a potential alternating between an anodic detection potential and a cathodic reactivation potential provided a more stable detector response for both anions. Potentials alternating in the ranges +0.85 to -0.30 V and +0.60 to -0.30 V were used for SCN- and SeCN-, respectively. The linear response ranges and the detection limits were 250 mu mol l(-1) and 0.8 mu mol l(-1) (at pH 2.0), respectively, for SCN-, and 0.2-20 mu mol l(-1) and 0.1 mu mol l(-1) (at pH 7.0), respectively, for SeCN-. Thiocyanate can be readily determined in saliva samples following 100-fold dilution with the supporting electrolyte solution. The results are comparable to those obtained using a standard spectrophotometric method.