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

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RSD5%;自然岩浆磁铁矿的测定结果与推荐值相比,多数元素的RSD7%,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。

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

Microscopic pore structures of shale are the basis of investigating the adsorption and migration mechanism of shale gas and building geological model. Ar ion milling combined with scanning electron microscopy is the main technique to carry out such researches. However, previous researches mainly focused on the pore classification,and pore structures still lacked quantification and needed further study. In this study, edge detection, watershed,auto and manual thresholding methods were adopted to perform pore segmentation of mineral matrix pore and organic matter pore based on secondary scanning electron images. By comparisons, the results indicated that manual thresholding method was more suitable for shale pore (>1 nm) segmentation. Thresholding could identify the organic matter, pores and brittle minerals accurately by selecting accurate segmentation thresholding value, guaranteeing the results converged to the true states and providing an effective method for shale pore structures quantification.