顶空气相色谱法测定生物柴油中甲醇和二甲苯含量

Determination of the contents of methanol and xylene in biodiesel by headspace gas chromatography

生物柴油是以C14~C24脂肪酸甲酯为主要成分,残留少量单脂肪酸甘油酯、二脂肪酸甘油酯、三脂肪酸甘油酯及其他微量杂质的复杂重组分体系。为避免上述重组分对分析结果的影响和干扰以及减少样品前处理步骤、提高测试效率,采用顶空气相色谱法同时快速测定生物柴油中微量甲醇与二甲苯含量。结果表明,在一定的顶空与色谱条件下,46 min内同时完成4组分（甲醇、对二甲苯、间二甲苯、邻二甲苯）的测试且具有良好的分离效果。甲醇在0.002%~1.038%（质量分数）之间、二甲苯（对二甲苯、间二甲苯、邻二甲苯）在0.001%~0.508%（质量分数）之间均呈现良好的线性关系,相关系数R2为0.999 7。各组分的最低检出限在0.001%~0.002%（质量分数）之间,相对标准偏差小于5%,加标回收率在98.8%~106.7%之间。定量数据的精密度良好,定量结果准确可靠,是测定生物柴油中甲醇与二甲苯含量的有效方法。

Biodiesel is a complex system containing C14 -C24 fatty acid methyl esters as the main ingredi- ents 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 - xy- lene） 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.