New Developments in Trace Analysis of Plant Materials

Poor sample transport efficiency severely limits the sensitivity in traditional flame atomic absorption spectrometry. An alternative is the Delves Microsampling Cup System which allows the introduction of the sample directly into the flame. The sample is vaporized as a discrete mass of material and passes into a heated silica or ceramic tube which maintains the atomic vapour within the light path of the atomic absorption spectrometer sufficiently long for good sensitivity to be achieved. Attempts at analysing solid (unground / untreated) samples of plant material have encountered many difficulties. Eastwood(1987), working without background correction, was unable to time resolve the smoke peak from the analyte peak and found that calibration against a slurry standard was unreliable when analysing unground solid discs of plant samples . An ashing step at 440 ⁰C was found to both remove the ash peak and to disrupt the whole solid sample sufficiently so as to allow calibration against slurried standards. Whilst Eastwood found no loss of lead at these temperatures, the risk, which will be more pronounced for other metals, still exists The variability of replicate determinations from ashed solid discs was considerably higher than that from ashed slurry samples. no doubt, partly due to the innate heterogeneity within any sample. This preliminary work attempted to follow a similar line to Eastwood, but using low temperature ashing in a stream of ozone to facilitate both sample homogeneity and the oxidation of organic matrix. Following ozone oxidation the samples are slurried in water or dilute nitric acid by the application if ultrasound. The intention is to apply these methods to study the distribution of metals in wetland plants grown as part of an experimental reed bed system