Flow injection amperometric determination of thiocyanate and selenocyanate at a cobalt phthalocyanine modified carbon paste electrode

Abstract

Inorganic anions containing sulfur (SO32–, S2O32–, 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 2–50 µmol l–1 and 0.8 µmol l–1(at pH 2.0), respectively, for SCN–, and 0.2–20 µmol l–1 and 0.1 µmol 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.