Flow injection-pulse amperometric detection of ephedrine at a cobalt phthalocyanine modified carbon paste electrode

Abstract

Direct detection of ephedrines and other underivatized amino compounds (amines, alicyclic amines, alkanolamines, and amino acids) can be carried out via electrocatalytic oxidation at a carbon paste electrode (CPE) modified with cobalt phthalocyanine (CoPC) in alkaline solution (0.10 mol L⁻¹ NaOH). Most of the amino compounds tested could be determined using the CoPC/CPE in an amperometric flow detector. The analytical signal of ephedrine was stabilised by alternating the potential between an anodic detection potential of +0.30 V (+0.45 V for other amino compounds) applied for 220 ms and a cathodic reactivation potential of −0.30 V applied for 100 ms (potentials versus SCE). The linear response range for ephedrine was within 1–100 μmol L⁻¹ and the detection limit was 0.8 μmol L⁻¹ with a 100 μL sample loop and a typical sampling rate of 60 h⁻¹. The signal (oxidation peak current) reproducibility was 2–3%. The method was applied to the determination of ephedrine in pharmaceutical formulations with results comparable to those obtained with a standard spectrophotometric method.