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

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(2,2,2'-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 x 10(-7)-1 x 10(-5) mol 1(-1) for the chemiluminescence method and 1 x 10(-7)-3 x 10(-5) mol 1(-1) for the ECL method. The limits of detection were 4.8 x 10(-8) mol 1(-1) for chemiluminescence and 4.4 x 10(-8) mol 1(-1) for ECL. A related fungicide tridemorph was also determined by ECL and the linear range for that was between 5 x 10(-7) and 5 x 10(-5) mol 1(-1), with a limit of detection of 4.5 x 10(-7) mol 1(-1). An interference study showed that the main interferences for both methods were ascorbic acid and oxalic acid that interfered at the 2 x 10(-6) and 1.0 x 10(-6) mol 1(-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.