Optimization of coprecipitation using response surface methodology in combination with experimental design for determination of trace Ni by flame atomic absorption spectrometry in biodiesel produced from waste cooking oil

Abstract

In this study, the Box-Behnken design (BBD) of the response surface methodology (RSM) has been used to optimize the coprecipitation variables (coprecipitation pH, Al:Ni mole ratio, injection speed of base) for preconcentation of Ni using aluminum hydroxide to obtain accurate quantitation of Ni in biodiesel samples produced from waste cooking oil (WCO) by homemade flame atomic absorption spectrometer. The performance of homemade flame atomic absorption spectrometer has been evaluated through comparison with Perkin-Elmer 5100 PC flame atomic absorption spectrometer using aqueous standard solution of Cu, Ni. The predicted optimal conditions of statistical are pH=10.5 and Al:Ni mole ratio of 1.96×10⁴, while the injection speed for NaOH is 0.85mL/min at the concentration of 1.0mol/L. The concentration of Ni is µg/L level and preconcentration factors is between 50~200. To assess the accuracy of purposed method, a recovery test has been performed and compared to analytical values of Perkin-Elmer 5100 PC GFAAS.