Simultaneous determination of cobalt and vanadium in undiluted crude oil using high-resolution continuum source graphite furnace atomic absorption spectrometry

A fast, simple and sensitive screening method for the simultaneous determination of Co and V in crude oil samples by high-resolution continuum source graphite furnace atomic absorption spectrometry is proposed. The simultaneous determination is possible as two secondary lines for V, at 240.674 nm and 240.789 nm, are in the vicinity of the most sensitive Co line at 240.725 nm and within the wavelength interval covered by the linear charge-coupled device array detector. The samples have been analyzed directly without dilution after a 10-minute homogenization in an ultrasonic bath. Aliquots of 0.6-8.0 mg have been weighed onto solid-sampling platforms and a chemical modifier solution of Pd and Triton X-100 has been added over the samples. Although the volatility of the two analytes is different, it has been no problem to find compromise conditions, i.e., a pyrolysis temperature of 1300 degrees C, and an atomization temperature of 2650 degrees C; aqueous standard solutions have been used for calibration. Two certified oil reference materials have been analyzed to validate the accuracy of the method, and the results were in agreement with the certified or reported values, according to the t-test for a 95% confidence level. The limits of detection (3 sigma, n = 10) were 8 mu g kg(-1) for Co and 1.2 mg kg(-1) for V, as a secondary, less sensitive line has been used for the determination of this element. Five crude oils samples were analyzed using the proposed procedure. The precision, expressed as RSD, ranged from 3 to 13% for Co, and from 7 to 24% for V, except for one sample, the V content of which was very close to the limit of quantification.