Determination of Anions and Cations in Biodiesel with On-line Sample Pretreatment Column-switching Ion Chromatography

Abstract

An ion chromatographic approach with on-line sample pretreatment column-switching technique was proposed for the determination of anions and cations in biodiesel. By the employment of the column-switching technique combined with a polymer-based reversed-phase column (An IonPac NG1 guard column), organic residues in the aqueous extracts of biodiesel samples could be on-line removed automatically before flowing into analytical columns. An IonPac AG 11–HC guard column and IonPac AS 11–HC separation column were utilized for the anion separation, whereas an IonPac CG 12A guard column and IonPac CS12A was utilized for cations. Under the optimized separation conditions, a series of standard solutions consisting of nine anions of various concentrations from 0.05 to 40 mg/kg were analyzed with correlation coefficients r ≥ 0.9990, as well as six cations of various concentrations from 0.05 to 20 mg/kg. The limits of detection were in the range of 3.2 to 23.3 µg/kg for anions and 5.1 to 31.3 µg/kg for cations. Relative standard deviations of both anions and cations for retention time, peak area, and peak height were less than 2.98%. A spiking study was performed with satisfactory recoveries between 88.6 and 104.0% for all ions. The chromatographic system was successfully applied to the analysis of five biodiesel samples.