A rapid and sensitive voltammetric determination of sulphur in biodiesel in samples no treated and treated with TMAH

The control of environmental pollution has demanded increasingly determination of sulphur in a variety of matrices. Different analytical methods have been developed for the determination of this analyte in biodiesel fuel using various analytical techniques, including spectroanalytic and chromatographic methods. In this work a square-wave cathodic adsorptive stripping voltammetric (SW-AdCSV) procedure is proposed for the determination of sulphur in biodiesel, using a glassy carbon electrode modified with mercury-film (MFE). A buffer solution containing sodium acetate 1.4 mol L−1 and acetic acid 2% was used as supporting electrolyte in two different media (methanol an propanol). The voltammetric measurements were performed adding 70 μL of biodiesel sample previously treated with tetramethylammonium hydroxide (TMAH) to the supporting electrolyte. The method showed good linearity (r = 0.998) in the determination of sulphur in biodiesel (medium-concentration of 2.68 × 10−8 mol L−1 (1.07 × 10−3 mg kg−1) for a confidential level of 95%. Low values of limit of detection-LOD (3.29 × 10−10 mol L−1 (1.32 × 10−5 mg kg−1) and limit of quantification-LOQ (1.10 × 10−9 mol L−1 (4.40 × 10−5 mg kg−1) indicate a good sensitivity of the method. A validation of the procedure was carried out by comparing this procedure with the results obtained by an official method, using the same sample, through Teste-t of Student (confidence level of 95%). These results indicated that both methods are statistically equivalent, thus demonstrating the feasibility of the new method.