Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland.
Talanta. 2011 Sep 30;85(4):2000-6. doi: 10.1016/j.talanta.2011.07.046. Epub 2011 Jul 19.
The determination of fatty acid methyl esters (FAME) in diesel fuel blends is an important aspect of production and blending process as well as quality control of distribution operations. In this study, energy-dispersive X-ray fluorescence spectrometer (EDXRF) is used for the first time for determination of FAME in biodiesel blends. The principle of the method is based on intensity difference of X-ray radiation scattered from hydrocarbons and from FAME. The experiment shows that coherent and incoherent radiation, commonly applied for evaluation of the average atomic number of the sample with light matrix, cannot be applied for FAME determination. However, the application of scattered continuous radiation gives excellent correlation between FAME concentration and intensity of scattered radiation. The best results are obtained if continuum is collected in the range of energy between 10.5 and 15.0 keV for rhodium X-ray tube, operated at 35 kV. Linear relationship between the FAME concentration and the inverse of scattered continuous radiation is obtained with the correlation coefficients of 0.999. Standard deviation of measurement is ca. 0.46% (v/v) of FAME and detection limit is 1.2% (v/v) for 600 s counting time and 50% dead-time loss using Si-PIN detector. The investigation shows that crucial issue in determination of FAME in biodiesel blends using EDXRF spectrometer is the precision of measurements resulting from the counting statistics. Therefore, much better results (0.20% (v/v) standard deviation and 0.52% (v/v) detection limit) can be expected if higher intensity of primary radiation is applied and X-ray spectrum is collected by silicon drift detector of high input count rate. For concentration of FAME from 10 to 100% (v/v), the differences between reference method (Fourier transform infrared spectrometry) and the proposed method usually do not exceed 1% (v/v) of FAME. The proposed method is fast, simple and enables FAME determination in wide range of concentration up to 100% of FAME without any sample treatment.
测定柴油燃料混合物中的脂肪酸甲酯（FAME）是生产和混合过程以及分销操作质量控制的重要方面。在本研究中，能量色散 X 射线荧光光谱仪（EDXRF）首次用于测定生物柴油混合物中的 FAME。该方法的原理基于从碳氢化合物和 FAME 散射的 X 射线辐射强度差异。实验表明，通常用于评估轻基体样品平均原子数的相干和非相干辐射不能用于 FAME 测定。然而，散射连续辐射的应用可获得 FAME 浓度与散射辐射强度之间的极佳相关性。如果使用铑 X 射线管在 35 kV 下操作，在 10.5 至 15.0 keV 的能量范围内收集连续谱，则可获得最佳结果。对于 rhodium X 射线管，在 35 kV 下操作，在 10.5 至 15.0 keV 的能量范围内收集连续谱时，可获得 FAME 浓度与散射连续辐射倒数之间的线性关系，相关系数为 0.999。使用 Si-PIN 探测器进行 600 s 计数时间和 50%死时间损失时，测量的标准偏差约为 FAME 的 0.46%（v/v），检测限为 1.2%（v/v）。研究表明，在使用 EDXRF 光谱仪测定生物柴油混合物中的 FAME 时，关键问题是测量的精度取决于计数统计数据。因此，如果应用更高强度的初级辐射并使用高输入计数率的硅漂移探测器收集 X 射线光谱，则可以获得更好的结果（标准偏差为 0.20%（v/v），检测限为 0.52%（v/v））。对于 FAME 浓度从 10 到 100%（v/v）的情况，参考方法（傅里叶变换红外光谱法）和建议方法之间的差异通常不超过 FAME 的 1%（v/v）。该方法快速、简单，无需任何样品处理即可在高达 100%FAME 的宽浓度范围内测定 FAME。
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