Electrochemical determination of free chlorine on pseudo-graphite electrode

Pseudo-graphite from the University of Idaho Thermolyzed Asphalt Reaction also known as GUITAR is a new form of carbon. It shares morphological features with graphites, including basal and edge planes. Unlike graphites and other sp²-hybridized carbons, GUITAR has fast heterogeneous electron transfer across its basal planes and resistance to corrosion similar to boron-doped diamond electrodes. In this contribution GUITAR electrodes were examined as sensors for aqueous free chlorine (HOCl and OCl^-) at pH 7.0 with cyclic voltammetric (CV) and chronoamperometric (CA) methods. Using CV at 50 mV s^-1 GUITAR has a limit of detection of 1.0 μmol L^-1, linear range of 0-5,000 μmol L^-1, sensitivity of 215.8 μA L mmol^-1 cm^-2 and a signal stability of 4 days in constant exposure to 1 mmol L^-1 free chlorine in pH 7.0, 0.1 mol L^-1 phosphate buffer system. After 7 days of exposure GUITAR electrodes lost 37% of the former sensitivity, which was recovered by an in-situ regeneration procedure. The common aqueous ions, Ca²⁺, Na⁺, NO₃^-, SO₄^2-, Cl^-, CO₃^2- and dissolved oxygen did not affect the response of the GUITAR-based sensor. The combination of limit of detection, linear range, sensitivity, sensor lifetime and its relative lack of interferences indicate that GUITAR is one of the best performers in free chlorine sensors.