Sequential Ionizing-direct Mass Spectrometry Analysis Of Ore Sample

The physical and chemical property of an element is closely associated with its existing form.Obtaining the speciation information of an element is helpful in knowing its physio-chemical property and biological activity more accurately.It can also provide a plenty of information for the deep study of the important scientific and technical problems in the fields of geoscience,environmental science,life science,and so on.Nevertheless,the conventional speciation analysis usually requires to treat the sample to separate different speciation of the element before a quantitative analysis.This results in a lengthy and inefficient analysis and more importantly,this can probably increase the uncertainty of the analytical result because of the key information loss due to the complicated sample processing.Recently,with the development of direct mass spectrometry,the molecular and quantitative information of an analyte in the complex sample matrix is obtained without pre-processing the sample.Direct mass spectrometry has been widely used in biomedicine,environmental monitoring,etc...However,it is scarcely used in the elemental speciation analysis.Therefore,by utilizing the strategy of direct mass spectrometry,this dissertation extracts sequentially the different species of an element in the geological and mineral sample without pre-processing the sample by adjusting the interaction selectivity and strength between the reagent and energy and the sample.The extracted elemental species are simultaneously transferred online to the inductively coupled plasma-mass spectrometry（ICP-MS）for ionization and mass spectrometry analysis.This dissertation mainly studies:1)Chemical speciation analysis of arsenic（As）in ferrihydrite.Arsenic is an important environmental pollutant.Obtaining chemical speciation of As is of great significance to assess its biological toxicity.With the home-made online sequential elution device,this chapter uses H₂O,NH₄NO₃,NH₄H₂PO₄,（NH₄）₂C₂O₄ and HF to extract effectively the water-soluble,non-specifically adsorbed,specifically adsorbed,iron oxide-complexed and residual As,respectively.The extracts are transferred online simultaneously to ICP-MS to analyze each As speciation quantitatively.The results demonstrate that water-soluble As is not detected in the sample and As exists mainly in a form binding with iron oxide（>80%）.There is also a certain amount of non-specifically-adsorbed and specifically adsorbed As（10%）.The detection limit of As（III）is 0.008μg·kg^-1 and that of As（V）is 0.013μg·kg^-1.The method has advantages of low sample consumption,high detection throughput and convenient and fast experimental procedure.It provides a new option for the chemical speciation analysis of As in solid matrix（for example,iron oxide,etc...）in a sensitive,fast and accurate manner.2)Chemical speciation analysis of rare earth elements（REE）in ion-adsorbing rare earth deposits.Obtaining the speciation of the rare earth elements in the rare earth ore samples is very important in the study of ore formation mechanism,in the assessment of ore grade and in the determination of mining method.Therefore,in this chapter,rapid fractionation analysis of 15REEs and accompanied metal（Fe,Mn,etc.）in ore samples has been achieved within 1 h using ICP-MS with a homemade device for online sequential solvent extraction.H₂O,CH₃COONH₄,NH₂OH·HCl,HNO₃/H₂O₂ and HF/HNO₃are sequentially used as the eluting reagent.Five fractionations for REEs occurrences,i.e.,water soluble,exchangeable,reducible,oxidizable and crystalline,have been identified,offering chemical insights which not only reveal the formation mechanism of REEs ores but also show great implications for guiding the exploitation and separation of REEs.In comparison with conventional methods,the present approach significantly shortened the analysis time（1 h vs.～80 h）and reduced the sample consumption（1.0 mg vs.5.0 g）with high recovery（>95%）,providing a useful platform for the rapid quantitative fractionation analysis of REEs in complexed samples such as ore,soil and fossils.3)Chemical speciation analysis of rare earth elements（REE）in dinosaur fossils.The distribution characteristic of rare earth elements（REEs）is widely used in provenance discrimination,taphonomy and palaeoenvironment evaluations.It is often used in the stratigraphy study such as stratigraphic dating in the vertebrate fossils.In this chapter,an online sequential ionization approach is constructed by the usage of home-made soft sequential ionizing device.We analyse the rare earth element speciation of the sample from the inner,middle and outer layer of the dinosaur fossils,respectively.The results show the rare earth elements in the fossil are mainly in oxidation states（>96%）.There is a small amount of elements that are in water soluble states（<1%）.The amount of elements in silicate-binding states is also small（<1%）.Meanwhile,the total amount of rare earth in outer layer is 10 times that in inner layer.The study indicates that the rare earth elements react with the calcium ions in the apatite by a substitution mechanism and enter the fossil via an isomorphism pathway.The rare earth ore is thus formed having strong chemical bonds.The substitution mechansim plays a major role in the accumulation of rare earth elements in fossils.The approach developed in this chapter is convenient and fast（1 h in analysis time）,consumes low amount of sample（1mg）and has high analytical precision.4)Direct mass spectrometry of uranium ore.Speciation of uranium can reflect the grade and leaching difficulty of uranium ore.In order to increase the element extraction efficiency for the geological and mineral samples,we further couple the energy control on the basis of the adjustment of the interaction between the reagent and the geological and mineral sample.This chapter uses the typical uranium ore as the research target and refines the sample holder module in the soft sequential ionizing device by adding a heating device to change extraction temperature.The extraction speed of the uranium element species are therefore enhanced and the direct mass spectrometry for uranium speciation analysis is achieved.The results show that the uranium content of Songliao ore is 149.6μg·g^-1 and that of alaskite in Namibia is 1579.2μg·g^-1.The accuracy of this method is high as verified by the comparison with the result for standard sample.The method’s precision is good（RSD<4%）.The result also shows that uranium exists mainly in an oxidized state,consistent with the fact that uranium ores are only stable in a reduced environment.The study on the sequential ionization mass spectrometry analysis of ferrihydrite,ion-adsorbing rare earth deposits,dinosaur fossil and uranium ore prove that the methods developed in this dissertation analyses samples fast and accurately,consumes low amount of samples and offers rich analytical information.They are applicable to online direct analysis of various ores without pre-processing samples.The application of the methods can extend to the fields of material,energy,environment,life science,etc...