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

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 microemulsions (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 mu L micro-emulsion aliquots are delivered to the graphite tube. The pyrolysis and atomization temperatures were set to 400 degrees C and 1400 degrees C, respectively. The calibration curves showed a linear response up to analyte concentrations of 150 mu g 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 mg 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 mg L-1. The proposed procedure was used for mercury determination in naphtha feeds processed in Braskem S. A. (Salvador, Bahia, Brazil).