Determination of total contents and volatile and non-volatile fractions of nickel and vanadium in gasohol by graphite furnace atomic absorption spectrometry after extraction induced by emulsion-breaking

Abstract

The determination of the total contents and volatile and non-volatile fractions of nickel and vanadium in gasohol by graphite furnace atomic absorption spectrometry (GF AAS) after extraction induced by emulsion-breaking (EIEB) is proposed. In the extraction procedure, a 0.5 mL aliquot of 6% (v/v) Triton X-114 solution diluted in 10% (v/v) HNO3 was added to 5.0 mL of a gasohol sample. The system was subjected to an ultrasonic bath for 10 min. The emulsion formed was broken at 90 °C, and the hydroalcoholic phase was collected for analysis. The determination of the total contents and non-volatile and volatile (by difference) fractions of nickel and vanadium was carried out by assessing the differences in the thermal behavior of the species during the pyrolysis step. Because the extracted phase was less complex than the original matrix, it was possible to use pyrolysis temperatures at 300 and 200 °C, in the presence of Pd(NO3)2, to determine the total contents of V and Ni, respectively. The thermostable (non-volatile) fractions were determined without the use of a modifier at higher pyrolysis temperatures (1700 and 1500 °C for V and Ni, respectively). For vanadium, the limits of detection, precision (% RSD, n = 8, 10 μg L−1) and values for the recovery test were 1.1 and 0.42 μg L−1, 5.8 and 3.4% and 96–108 and 100–108% for the total content and non-volatile fraction, respectively. For the nickel, the limits of detection, precision (% RSD, n = 8, 10 μg L−1) and values for the recovery test were 3.5 and 1.7 μg L−1, 9.6 and 2.0%, and 86–101 and 91–109% for the total content and non-volatile fraction, respectively. Enrichment factors between 2.5 and 5.0 times were found for both metals. This method was applied to the determination of the total contents (3.70–31.98 and 15.71–126.1 μg L−1), non-volatile fractions (2.16–14.33 and 2.00–10.99 μg L−1) and volatile fractions (1.54–20.54 and 13.71–115.1 μg L−1) of vanadium and nickel, respectively, in gasohol samples.