Avaliação de procedimentos para preparo de amostras agronômicas visando determinação multielementar por espectrometria de emissão ótica com plasma induzido.
Abstract
Sample preparation was always considered a limiting factor for sample
throughput in the analytical sequence due to its high time consumption and great
probability for error insertion in the results. Therefore, purposes to generate
lower analysis time and, mainly, to make sample handling a feasible process are
readily wished. Two procedures for preparation of agricultural samples (bovine
milk and fruit juices) for multielemental determination by inductively coupled
plasma optical emission spectrometry have been investigated. A procedure for
bovine milk treatment based on use of proteolytic enzymes (pepsin) and protein
precipitator agent (trichloroacetic acid) for extraction of Ca, Fe, Mg, and Zn was
investigated. Application of these reagents allowed to check the complex
interaction between Fe and milk proteins. Quantitative determinations from
simple protein precipitation in solution showed good results for Ca, Mg, and Zn.
Results obtained for Fe, using protein precipitation, confirmed the strong bound
of this element with the casein micelle. In general, the recovery of Fe on protein
precipitate was around 100 %. Taking into account the procedure for fruit juices
treatment, a flow system operating at high temperature and high pressure was
developed. This system presented decomposition efficiency around 99 % for
different carbon sources when 300 oC and 60 bar was applied. As result, it can
be suggested that the use of diluted nitric acid (HNO3 1.4 mol L-1) associated to
hydrogen peroxide as auxiliary oxidant agent (H2O2 3.0 % v v-1), does not
compromise the decomposition efficiency if high temperature is applied.
Recoveries of Ca, K, Mg, and Na in the digestates obtained by the flow system
were in agreement with those found in the closed vessel-MW assisted acid
decomposition. The flow system behavior for vegetal tissues slurries
decomposition was also evaluated. At the same time the spectrometers
performance was evaluated. Figures of merit, warm up time, long and short term
stability, spectral resolution, and limit of detection were compared for axially-
and radially-viewed configurations. The performed experiments showed similar
performance for both configurations, differing only on the warm up time and
limit of detection. Taking into account the obtained results it is possible to infer
that most of the applications performed with the radially-viewed configuration
could be carried out in axially-viewed ICP OES s with no analytical
performance degradation.