Mercury determination in petroleum products by electrothermal atomic absorption spectrometry after in situ preconcentration using multiple injections

Abstract

A simple method for mercury determination in petroleum fractions (e.g. naphtha) using electrothermal atomic absorption spectrometry (ETAAS) associated with multiple injection technique for direct preconcentration in the graphite tube has been developed. Oil-in-water micro-emulsions (three-component solutions) were prepared using a mixture of sample, propan-1-ol and HNO₃. No additional sample pretreatment was required. In the procedure, three successive 30 μL micro-emulsion aliquots are delivered to the graphite tube. The pyrolysis and atomization temperatures were set to 400 °C and 1400 °C, respectively. The calibration curves showed a linear response up to analyte concentrations of 150 μg L⁻¹ with a correlation coefficient of 0.993. The precision calculated from fifteen consecutive measurements and defined as the coefficient of variation of solutions containing 5.0 and 30 μg L⁻¹ of Hg were 6.4% and 4.7%, respectively. The limit of detection (LOD), defined as the Hg concentration that gives a response equivalent to three times the standard deviation (s) of the blank (n = 10), was found to be 0.78 μg L⁻¹. The proposed procedure was used for mercury determination in naphtha feeds processed in Braskem S.A. (Salvador, Bahia, Brazil).