Determination of total phosphorus in biodiesel by ion chromatography

Abstract

Phosphorus content in biodiesel is an important parameter for evaluating its quality. In this paper, the total amount of phosphorus in biodiesel was determined by Ion Chromatography (IC) with on-line matrix elimination function. An effective and safe sample pretreatment method and IC quantification method were adopted. The method has good linear correlation (r = 0.9998), low detection limit (Cmin = 0.007 mg L−1) and reasonable reproducibility. By measuring the residual carbon of biodiesel ashing products at different temperature points as an index of ashing degree, phosphate from biodiesel ashing products at different temperature points was determined by IC; the optimum ashing temperature was 680 °C. At 680 °C, the amount of phosphorus in Jatropha curcas biodiesel was determined by both IC and ICP-OES; the measured phosphorus content was 13.53 mg·kg−1 and 11.25 mg·kg−1, respectively, and exceeded the national standard of 10 mg·kg−1. In addition, the phosphorus content of soybean oil biodiesel was tested by IC at different ashing temperatures. Those results showed that at 680 °C, the biodiesel phosphorus content in soybean oil was 5.41 mg·kg−1, lower than the 10 mg·kg−1 stipulated by ASTM D 6751 and GB 25199, but higher than the 4 mg·kg−1 stipulated by EN14214.