| Biodiesel is a complex system containing C14~C24 fatty acid methyl esters as the main ingredients with a bit residues of monoglycerides, diglycerides, triglycerides and other trace impurities. In order to avoid the disturbance of the above heavy components, facilitate the sample pretreatment and improve testing efficiency, the headspace gas chromatography was used to simultaneously determine the contents of methanol and xylenes in biodiesel quickly. The results showed that under proper headspace sampling and chromatographic conditions, the four components (methanol, para-xylene, meta-xylene, ortho-xylene) were well separated in 46 min. It presented excellent linear relationships for methanol in the range of 0.002%-1.038% (mass fraction) and xylenes (para-xylene, meta-xylene and ortho-xylene) in the range of 0.001%-0.508% (mass fraction). The correlation coefficient R2 was 0.999 7. The lowest limit of detection of each component was in the range of 0.001%-0.002% (mass fraction); moreover, the relative standard deviations were less than 5% and the standard addition recoveries were in the range of 98.8%-106.7%. Thus, a reliable method for determining the contents of methanol and xylene in biodiesel was established with good precision and repetition. |
