Voltammetric behaviour of the synthetic pyrethroid lambda-cyhalothrin and its determination in soil and well water

The pyrethroid lambda-cyhalothrin is a common insecticide which is widespread in the environment. A study of the electrochemical reduction of the pesticide on a hanging mercury drop electrode (HMDE) was performed as basis for the development of a sensitive analytical method for determination of lambda-cyhalothrin in natural samples. Two electrochemical techniques—cyclic voltammetry (CV) and differential pulse voltammetry (DPV)—were applied. The study was performed in the pH range 2–13 using Britton–Robinson (B–R) buffer to control the pH of the measuring solutions and tetrabutylammonium chloride (TBAC) salt as supporting electrolyte. In DPV, a single reduction peak was observed at both pH<4.0 and pH>10.5 while two cathodic peaks were produced in the pH range 4.0–10.5. The results showed that the reduction of lambda-cyhalothrin in the measuring solution is irreversible. The limiting current was found to be diffusion-controlled and free of adsorption of the electroactive species to HMDE over the whole pH range tested. For the analytical DPV method running at pH 2 the relationship between peak current and lambda-cyhalothrin concentration was linear up to 500 (mu)g l^-1 (1.1×10^-6 mol l^-1) with a detection limit of 2.5 (mu)g l^-1. The repeatability in terms of relative standard deviation (n=10) was in the order of 3.5% at concentration levels of 5 and 10 (mu)g l^-1. A DPV method for determining lambda-cyhalothrin in the agrochemical formulation Karate, spiked soil and well water was developed. The recovery was about 94% in well water and 92% in soil samples at concentration range of 0.05–0.5 (mu)g l^-1 and 0.05–0.5 (mu)g g^-1, respectively.