Calibration Techniques and Modifiers for the Determination of Cd, Pb and Tl in Biodiesel as Microemulsion by Graphite Furnace Atomic Absorption Spectrometry

Different calibration approaches and modifiers were tested for Cd, Pb and Tl determination in biodiesel by graphite furnace atomic absorption spectrometry (GF AAS). Microemulsions were prepared by mixing 2 g of biodiesel, 1 mL of a 10% (v/v) nitric acid aqueous solution and n-propanol to a 10 mL final volume. Pyrolysis temperatures of 600 degrees C for Cd and Tl with Pd as permanent modifier, and 800 degrees C for Pb with Ru as permanent modifier were used. Atomization temperatures were also optimized. Calibration solution prepared in aqueous medium did not correct non-spectral interferences, but matrix matching calibration using base oil led to accurate results with recoveries from 80 to 116%. The RSD values were lower than 8% for Cd and Pb and the LOD values were 0.5 ng g(-1) for Cd, 6 ng g(-1) for Pb and 1 ng g(-1) for Tl. The obtained results using the analyte additions method or by matrix matching calibration were in agreement, confirming the accuracy of the proposed procedure. Organometallic standards were not required and different samples were analyzed.