A new spectrophotometric method for determination of biodiesel content in biodiesel/diesel blends

In this paper a new quantitative analytical method is described for determining the biodiesel content in biodiesel/diesel mixture through of the fatty acid methyl ester reaction with hydroxylamine hydrochloride and iron(III) nitrate. The ferric hydroxamate complex diluted in n-heptane was analyzed by UV-visible spectroscopy in a range of 420-440 nm wavelength to determine the biodiesel content in biodiesel/diesel blends. The method has shown excellent repeatability and linearity for determining biodiesel content in biodiesel/diesel blends in the 0.5-5.0% quantification range and in small intervals of biodiesel content in diesel oil (0.1%). For levels over 5% of biodiesel in biodiesel/diesel blends, the linearity and repeatability is also excellent but it is necessary to increase the dilution of n-heptane of the ferric hydroxamate complex to still obtain a linear relationship between concentration and absorbance. The results obtained for biodiesel produced from different feedstocks are very similar, except for biodiesel produced from castor oil, what means that the method purposed has low influence of the feedstock used in biodiesel production. The parameters evaluated indicate that the method proposed is analytically reliable for determining biodiesel content in biodiesel/diesel blends.