Refractory Mineral Laser Sample Preparation-gas Mass Spectrometry Oxygen Isotope Composition Analysis Method

The complex composition of refractory minerals requires high temperature for reaction.The analysis of oxygen isotopic composition using conventional BrF₅method demonstrates that such method bears the disadvantages of large sample consumption,multiple influence factors,potentional pollution to the reaction devices and possible safety hazards,etc.Currently,the analysis of oxygen isotopic conposition trends toward microscale and microzone on the basis of the conventional BrF₅ method,by using laser heating.Laser BrF₅ method boasts the advantages of small sample consumption,fast fusion,high analysis efficiency as well as available for monitoring the entire reaction process,which altogether makes it suitable for analyzing the oxygen isotopic composition of refractory minerals.The thesis is designed to define reaction temperature and influence factors by using conditional BrF₅ method.The experimental devices for Laser BrF₅ have been designed and the method of Laser Sampling-Gas Mass Spectrometry for analyzing the oxygen isopotic composition of refractory minerals has been established.Details are presented as follows.The thesis makes a detailed dicussion on the optimum reaction temperature of refractory minerals,the influence of iron-bearing mineral on the reaction devices as well as the influence from the environmental humidity by using conventional BrF₅method.The optimum reaction temperature for some refractory minerals by conventional BrF₅ method is well defigned.For instance,the optimum reaction temperature for garnet is 600⁶80?,olivine 670⁶90?,quartz 550⁶40?and magnetite 650⁶80?.The analysis of ore-bearing samples heavily pollutes the pipeline,which causes inaccuracy on the test results of the subsequent samples.By analyzing the standard quartz samples of GBW04409 in each month of the year,it is concluded that the higher the environmental humidity is,the lower the value of?¹⁸O is and the highest humidity falls in the months of July and August.With reference to the existing experimental devices for conventional BrF₅method and Laser BrF₅ method,the author designs the devices for the analysis of oxygen isotopic composition by using Laser BrF₅ method.The laser pod is featured by fast exaction of oxygen isotopes from trace minerals,easy disassemly designed and quick vaccum.If suitable laser heating made were chosen and such parameters as laser enegy,size of beam spot,dosage of fluoridant,size and dosage of the samples as well as reaction time were set perfectly,refractory minerals would fully react with BrF₅ reagents.Laser BrF₅ method has been adopted to analyze the oxygen isotopic composition of such standard matter as Penglai zircon,Bixiling garnet,olivine,garnet and wolframite.The result shows that the analyzed value of the aforementioned stardand metter is consistent with the theoretical value.The test results for olivine and garnet of the both methods?conventional BrF₅ and laser BrF₅?are consistent,yet,the consistency for wolframite falls short.In addition,the experiment results are further discussed and reassessed by integrating the features from EPA,spectrometry and backscattering of the refractory minerals.All in all,it comes to the conclusion that Laser BrF₅ method is applicable to the analytical test of the oxygen isotopic composition of refractory minerals and the method of Laser Sampling-Gas spectrometry for the analysis has been established.