Liquid–liquid extraction is proposed as a clean sample preparation procedure for the determination of Na, K, Ca, and Mg in biodiesel by line source flame atomic absorption spectrometry (LS FAAS) and of Na and K by flame photometry (FP). A full 2³ factorial design was used to optimize the sample preparation. The investigated variables were the temperature effect, the use of acid and the stirring time for the extraction of metals in biodiesel. The sample preparation method essentially consisted of extracting metals from biodiesel with an aqueous solution of HNO₃ (1%, v/v) at 25 °C and manual agitation for 4 min. The instrumental limits of detection (LODs) for LS FAAS and FP were in the ranges 0.04–0.21 and 0.18–0.36 mg kg⁻¹, respectively. The accuracy of the method was checked by means of addition and recovery tests, and the recovery results for LS FAAS and FP varied from 80 to 114%, with RSD less than 14%. No significant differences were observed (p = 0.05) between the results obtained by the proposed technique and a comparative method. Interlaboratory studies were performed using different instruments, different samples and the same analyst. For this, addition and recovery tests and CRM analyses were performed by high resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS) and FP. The recoveries varied from 84 to 107%, with RSD less than 11% and the results for Na, K, Ca and Mg were in agreement with the certified values at the 95% confidence level (t-test; p < 0.05). The findings indicate that the liquid–liquid extraction method is reproducible, simple, and clean, and can be used as an alternative method of sample preparation for the determination of Na, K, Ca, and Mg in biodiesel samples.

中文翻译：

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液液萃取作为测定生物柴油中Na，K，Ca和Mg的样品前处理程序

建议采用液-液萃取作为一种清洁的样品前处理程序，用于通过线源火焰原子吸收光谱法（LS FAAS）测定生物柴油中的Na，K，Ca和Mg，通过火焰光度法（FP）测定钠和K中的钠和钾。完整的2 ³析因设计用于优化样品制备。研究的变量是温度效应，酸的使用和搅拌时间，以提取生物柴油中的金属。样品制备方法主要包括在25°C下用HNO ₃（1％，v / v）的水溶液从生物柴油中提取金属，并手动搅拌4分钟。LS FAAS和FP的仪器检出限（LOD）在0.04–0.21和0.18–0.36 mg kg ^-1之间， 分别。通过添加和回收率测试检查了该方法的准确性，LS FAAS和FP的回收率从80％到114％不等，RSD不到14％。通过所提出的技术和比较方法获得的结果之间没有观察到显着差异（p = 0.05）。实验室间研究是使用不同的仪器，不同的样品和同一位分析人员进行的。为此，通过高分辨率连续谱源火焰原子吸收光谱仪（HR-CS FAAS）和FP进行了添加和回收测试以及CRM分析。回收率从84％到107％，RSD小于11％，Na，K，Ca和Mg的结果与95％置信度下的认证值一致（t检验；p<0.05）。研究结果表明，液-液萃取方法具有可重复性，简单性和清洁性，可作为测定生物柴油样品中Na，K，Ca和Mg的另一种样品前处理方法。