无内标-多外标校正激光剥蚀等离子体质谱法测定磁铁矿微量元素组成

Determination of Trace Elements in Magnetite by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry Using Multiple External Standards without an Internal Standard Calibration

激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)常用于磁铁矿原位微量元素分析,按照校正策略不同,主要分为内标法和无内标法。内标法需要用电子探针(EMPA)预先测定磁铁矿中内标元素Fe的含量,过程较繁琐,且待测元素含量会受到内标元素含量测定的影响。本文采用铁含量较高的玄武质玻璃BCR-2G、BIR-1G、BHVO-2G和GSE-1G作为外标,避免了内标元素含量的测定,建立了无内标-多外标校正LA-ICP-MS测定磁铁矿微量元素组成的分析方法。利用该方法测定了科马提岩玻璃GOR-128g和自然岩浆磁铁矿BC 28的微量元素组成以评估方法的可靠性。结果表明,科马提岩玻璃的测定结果与推荐值及前人内标法的测定值一致,多数元素的相对标准偏差RSD<5%;自然岩浆磁铁矿的测定结果与推荐值相比,多数元素的RSD<7%,低于前人内标法的RSD(<15%)。由此说明无内标-多外标法可以实现富铁硅酸岩或磁铁矿微量元素含量的准确校正,克服了基体效应的影响。因此,无内标-多外标法是一种原位测定磁铁矿微量元素含量的快速、准确方法,具有一定的应用潜力。

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry（ LA-ICP-MS） is commonly used to analyze trace elements in magnetite,which can be divided into internal standard（ IS） and no internal standard（ NIS）methods according to calibration techniques. IS method involves a relatively complex process for the determination of Fe content by Electron Microprobe. Moreover, elemental content are affected by the analytical accuracy of IS elemental iron. An analytical method for determination of trace elements in magnetite by LA-ICP-MS using multiple external standards（ basaltic glasses BCR- 2G,BIR- 1G,BHVO- 2G,GSE- 1G） without an IS element has been developed. The proposed method avoids the determination of the IS element. Trace element compositions of komatitic glass（ GOR- 128g） and natural magmatic magnetite（ BC 28）were determined by the proposed method and used to evaluate the reliability of the method. Results show that the analytical values of komatitic glass are consistent with the certified values and reported values by the existing IS method. The relative standard deviation（ RSD） of most elements is smaller than 5%. Most elements of natural magmatic magnetite have RSD better than 7% between the analytical values and the certified values,and RSD better than 15% between the analytical values and the reported values by the IS method. This indicates that multiple external standards without an IS method can determine accurate calibration of trace element concentrations of iron-rich silicates and magnetite,overcoming the matrix effects. Therefore,multiple external standards without an IS method is a fast and precise method for determination of trace elements in magnetite,which has a great application potential.