A carbon paste electrode modified with kaolin for the detection of diquat

A carbon paste electrode modified with kaolin was employed for the quantification of diquat from aqueous solutions. The new electrode (K-CPE) revealed interesting electroanalytical detection of diquat based on the adsorption of this herbicide onto kaolin under open circuit conditions. The diquat reduction peaks were observed around − 0.69 V and − 0.97 V respectively for peaks P 1 and P 2 (vs. SCE) in 0.1 mol L − 1 K 2SO 4 using square wave voltammetry. The response depends on the concentration of diquat in the bulk solution as well as the parameters involved in the preconcentration, pH and the measurement steps. The best results were obtained under the following optimized conditions: 5 min accumulation time, 5 mV pulse amplitude, 1 mV s − 1 scan rate in 0.1 mol L − 1 potassium sulfate. Using such parameters a linear dynamic range up 80 mol L − 1 diquat was observed with a detection and quantification limits of 4.21 × 10 − 9 mol L − 1 and 3.55 × 10 − 8 mol L − 1 respectively. The recovery (I%) was obtained by spiking natural water with 2 × 10 − 5 mol L − 1 diquat.