Fast sequential determination of manganese and chromium in vegetable oil and biodiesel samples by high-resolution continuum source graphite furnace atomic absorption spectrometry

Abstract

A fast method for the sequential determination of Mn and Cr in vegetable oil and biodiesel samples using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) was developed. Propan-1-ol, propanone and methyl isobutyl ketone (MIBK) were evaluated as solvents for diluting the samples in different proportions to reduce the viscosity of the samples. MIBK was established as a diluent in a proportion of 40% (v/v). All measurements for the determination of Mn and Cr were performed sequentially using their main atomic lines at 279.4817 and 357.8687 nm, respectively. Two atomization temperatures were used sequentially, 1900 and 2500 °C for Mn and Cr, respectively, due to differences in their volatilities. Mg was employed as a modifier to avoid the loss of Cr and to obtain the best conditions for pyrolysis and atomization. The developed method allowed for the sequential determination of both metals in different types of vegetable oil and biodiesel samples, and it presented limits of quantification of 4.48 and 3.57 ng g⁻¹ for Mn and Cr, respectively. Addition and recovery tests were performed, and the results ranged from 79 to 108% for Mn and from 79 to 115% for Cr. The matrix effect was evaluated by comparing organic and aqueous calibration curves, and the results indicated that external calibration was possible. Vegetable oil and biodiesel samples were analyzed by the proposed method and another procedure using acid digestion, and the results from the two methods were consistent. The proposed method was applied for the determination of Mn and Cr in commercial vegetable oil and biodiesel samples produced from soybean, canola, sunflower and corn.