Electroanalytical stripping techniques have been well-used for trace-metal determinations, because of their
remarkable sensitivity and selectivity. However, when these techniques are applied for organic materials, such
as crude oil and petroleum-based fuels, the samples must be decomposed. This paper evaluates the use of
different microwave ovens for the decomposition of crude oil and diesel fuel to determine the content of
copper, lead, mercury, and zinc in the digestates. A focused-microwave (FM) oven using H2SO4/HNO3/H2O2,
operated at atmospheric pressure, and a closed-vessel microwave (CVM) oven using HNO3/H2O2, operated
under pressure in a vessel, were evaluated. Square-wave stripping voltammetry (SWSV) and stripping
chronopotentiometry (SCP) at gold film electrodes were applied for copper, lead, and mercury. Potentiometric
stripping analysis (PSA) at mercury film electrodes was applied for copper, lead, and zinc. SWSV was more
affected by residual organic matter, especially for lead determination. SCP presented higher sensitivity for
copper and mercury at gold electrodes. PSA at mercury electrodes was preferred for lead and zinc determination.
Better detection limits were attained for FM-digested solutions, after 0.8−1.0 g of sample can be digested, in
contrast to the low quantities (0.10−0.25 g) used when pressurized vessels were explored. Nevertheless, the
loss of mercury was verified when samples were decomposed in the FM oven.
Recebido em 23/1/02; aceito em 17/4/02 CLAY SLURRIES ANALYSIS USING INDUCTIVELY COUPLED PLASMA OPTICAL EMISSION SPECTROMETRY WITH AXIAL VIEW CONFIGURATION. The goal of this study was to evaluate the feasibility of direct introduction of clay slurries in an inductively coupled plasma optical emission spectrometer with axial view configuration. Calibration was performed using a certified reference material with a mean particle size of 13 µm (IPT-42) and the analytical curve was applied for quantification of two others reference materials (IPT-28 and IPT-32) and four samples. It was demonstrated that the analytical curve thus obtained was not completely suitable for IPT-28 and samples due to different mineralogical phases determined by X-ray diffraction. After considering this effect, it was possible for most elements to obtain results in agreement with certified values or with values obtained by a conventional technique at a 95% confidence level. It was demonstrated that the ICP-OES with axial view configuration did not present any incompatibility with the direct introduction of a complex inorganic suspension.
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