Voltammetric Determination of the Insect Repellent Dipropyl Pyridine-2,5-dicarboxylate in Non-aqueous Solvents

Abstract

The insect repellent di-propyl pyridine-2,5-dicarboxylate (MGK 326) may be reduced in aprotic acetonitrile at glassy carbon, platinum and hanging mercury drop (HMDE) electrodes to give an analytically ideal, reversible one-electron process with a reversible potential (E°′ value) of –1840 mV versus Ag/Ag⁺. In contrast, the reduction of MGK 326 in the protic solvent methanol and acetonitrile containing a molar excess of phenol occurs as a single two-electron chemically irreversible step. The addition of a proton source to acetonitrile can be observed to cause irreversibility in the reduction of MGK 326 with an accompanying positive shift in the reduction potential. Thus, in the presence of a proton source, the initially formed radical anion is protonated and further reduced at a potential less negative than the E°′ value. The reduction process in acetonitrile at a glassy carbon electrode was applied to the selective determination of MGK 326 in a commercial insect repellent formulation. Using differential-pulse voltammetry, a concentration of 41.4

g l^–1 with an RSD of 4.6% was obtained, compared with the concentration of 41.8 g l^–1 stated by the manufacturer. The limits of detection (3ς) of MGK 326 in acetonitrile, using differential-pulse voltammetry, were 7.2 × 10^–7M at an HMDE and 1.4 × 10^–6M at a glassy carbon electrode. The limits of quantification (10ς) were 1.8 × 10^–6 and 4.3 × 10^–6M at an HMDE and a glassy carbon electrode, respectively.