The measurement of multiple spray deposits by sequential application of metal chelate tracers

Chelates of the transition metals copper, cobalt, manganese and zinc, available as foliar feeds, were identified as the most suitable spray tracers for comparisons of deposits arising from up to four sequential applications to a single target. Their use minimised many of the disadvantages associated with other commonly used tracers such as visible and fluorescent dyes, and it was possible to quantify each tracer when present on the target in ratios of up to 100: 1. Each spray solution contained a single chelate at a metal concentration of 1 g litre(-1). The recovery of metal chelates from plant tissue may not be quantitative, as a consequence of absorption or adsorption by leaves for example. The food colorant tartrazine, at a concentration of 10 g litre(-1), was shown to be a suitable internal standard for estimation of percentage recovery. Combined spray deposits were recovered readily from apple leaves and fruit by aqueous extraction and analysed by atomic absorption spectroscopy. The spray deposit of each metal tracer was calculated from the raw analytical data using procedures for generating calibration curves designed to optimise the accuracy of the analysis.