Division of Metrology in Chemistry, National Institute of Metrology, Beijing 100013, China.
J Chromatogr A. 2013 Feb 15;1277:69-75. doi: 10.1016/j.chroma.2012.12.038. Epub 2013 Jan 3.
Identification and quantification of related-structure impurity is a research focus in the purity assessment of organic compounds. Determination of the purity value and uncertainty assessment are also important in the metrological research. A method for the determination of related-structure impurity in pure aldrin sample has been developed by using heart-cut multi-dimensional gas chromatography-mass spectrometry (MDGC/MS). Compared to the traditional one-dimensional (1-D) GC system, the two separated columns in the MDGC/MS system can effectively reduce co-elution, enhance separation capability, and thus improve detectability of the trace-level impurities. In addition, MDGC/MS system was simultaneously equipped with flame ionization detector (FID) or electron capture detector (ECD) in the first GC unit and mass spectrometry (MS) detector in the second GC unit. Therefore, accurate quantitative results of the trace-level impurities can be easily achieved by isolation of principal component to the second dimension column using "heart-cut" process. The mass fraction of related-structure impurities in aldrin samples obtained using MDGC/MS system ranged from 6.8×10⁻³ mg g⁻¹ to 26.47 mg g⁻¹ with five orders of magnitude, which is hard to be realized by mean of the 1-D GC. Excellent linearity with correlation coefficients of above 0.999 was achieved for each impurity analysis over a wide range of concentrations. Limits of quantification (LOQ) varied from 250 ng g⁻¹ to 330 ng g⁻¹ for FID, and from 1.0 ng g⁻¹ to 2.0 ng g⁻¹ detected by ECD. The combined standard uncertainty (u(c)) was lower than 0.37 mg g⁻¹ and 0.040 mg g⁻¹ detected using FID and ECD, respectively. Therefore, performance characterization of MDGC/MS used in the study is fit for quantification analysis of trace-level impurity. These results demonstrate that the MDGC/MS is extremely suitable for the purity assessment of organic compounds with medium structural complexity and low polarity.
鉴定和定量有关结构杂质是有机化合物纯度评估的研究重点。纯度值的测定和不确定度评估也是计量研究中的重要内容。本研究采用中心切割多维气相色谱-质谱联用（MDGC/MS）方法测定纯艾氏剂中有关结构杂质。与传统的一维（1-D）GC 系统相比，MDGC/MS 系统中的两个分离柱可以有效减少共洗脱，提高分离能力，从而提高痕量杂质的检测能力。此外，MDGC/MS 系统在第一根 GC 柱上同时配备火焰离子化检测器（FID）或电子俘获检测器（ECD），在第二根 GC 柱上配备质谱（MS）检测器。因此，通过“中心切割”过程将主成分分离到第二根色谱柱上，可以很容易地实现痕量杂质的准确定量结果。用 MDGC/MS 系统测定艾氏剂样品中有关结构杂质的质量分数范围为 6.8×10⁻³ mg g⁻¹26.47 mg g⁻¹，跨越 5 个数量级，这是一维 GC 难以实现的。每种杂质在较宽浓度范围内的分析均具有良好的线性关系，相关系数均大于 0.999。FID 的检出限（LOQ）为 250 ng g⁻¹330 ng g⁻¹，ECD 的检出限为 1.0 ng g⁻¹~2.0 ng g⁻¹。使用 FID 和 ECD 时，组合标准不确定度（u(c)）分别低于 0.37 mg g⁻¹和 0.040 mg g⁻¹。因此，本研究中使用的 MDGC/MS 的性能特征适合痕量杂质的定量分析。这些结果表明，MDGC/MS 非常适合中等结构复杂性和低极性的有机化合物的纯度评估。
