Determination of morpholine fungicides using the tris(2,2′-bipyridine) ruthenium(ii) chemiluminescence reaction

Abstract

Chemiluminescence and electrogenerated chemiluminescence (ECL) methods based on the tris(2,2′-bipyridine) ruthenium(II) chemiluminescence reaction were compared for the analysis of morpholine fungicides. Both methods proved to be sensitive and selective for the determination of dodemorph. In the chemiluminescence system the tris(2,2′-bipyridine) ruthenium(II) was oxidised with Ce(IV) and the flow rate, coil length and pH were optimised by a multivariate method. In the ECL system, the tris(2,2′-bipyridine) ruthenium(II) was oxidised at an aluminium working electrode. The calibration characteristics of the two methods were similar. The linear range was between 2 × 10⁻⁷–1 × 10⁻⁵ mol l⁻¹ for the chemiluminescence method and 1 × 10⁻⁷–3 × 10⁻⁵ mol l⁻¹ for the ECL method. The limits of detection were 4.8 × 10⁻⁸ mol l⁻¹ for chemiluminescence and 4.4 x10⁻⁸ mol l⁻¹ for ECL. A related fungicide tridemorph was also determined by ECL and the linear range for that was between 5 × 10⁻⁷ and 5 × 10⁻⁵ mol l⁻¹, with a limit of detection of 4.5 × 10⁻⁷ mol l⁻¹. An interference study showed that the main interferences for both methods were ascorbic acid and oxalic acid that interfered at the 2 × 10⁻⁶ and 1.0 × 10⁻⁶ mol l⁻¹ level, respectively. Good recoveries (96–100%) were obtained for the determination of dodemorph on cotton gloves and laboratory coats although a methanol extraction was used for the chemiluminescence method and a water extraction for the ECL method. This was because methanol depressed the ECL signal. A study of dodemorph uptake in barley was also carried out. Although ECL was the more elegant method for analysis it was less tolerant to methanol and this could be a disadvantage if it were required to extract the analyte from the sample.