Direct determination of phosphate in raw Jatropha curcas oil by ion chromatography

Raw Jatropha curcas oil is a promising feedstock for biodiesel, and its quality assessment is essential. The phosphorus content, especially that of organic phospholipids is one of the important quality parameters. Nevertheless, there is no standard method for measuring phospholipids directly, and the existing standards for content and measurement are for total phosphorus. In this study, a new method was developed to measure the content of inorganic phosphate in oil samples, by direct injection of solvent extracted oil into ion chromatography. Meantime, the total phosphorus content in oils was measured by the ISO 10540 standard molybdate colorimetric method, and the content of organic phospholipids can be derived by the difference between the total phosphorous and phosphate content. Various J. curcas seeds were obtained from the South-East Asia regions, and the raw oil therein was extracted and separated. Oils were dissolved in acetone and an ion chromatography system with sample matrix elimination function was applied to directly determine their phosphate content against acetone based standards. The results show that the J. curcas raw oils tested had phosphate contents ranging from 3 to above 50 mg kg−1, and the total P content of 30 to over 400 mg kg−1. Compared to the water-oil extraction procedure previously used for phosphate measurement in oil, this new method was simple, less labor-intensive, reasonably accurate and reliable for practical applications in biodiesel industries.

► A new IC method was developed to directly measure phosphate in biodiesel feedstock.
► The IC can eliminate solvent in the sample matrix and measure ions therein.
► Good linearity, detection limit, and reasonable reproducibility were obtained.
► PO43− and total P contents of 10 raw Jatropha curcas oils were measured.
► The new method was fast, simple, less labor-intensive, accurate and reliable.