Efficient Pretreatment Technologies For Whole Rock And In-situ ICP-MS Analyses: Design And Development Of Multifunctional Reagent Purification System And Soft Laser Ablation Cell

In the field of earth science and related areas,accurate data is the basis,and efficient pretreatment technique for geological samples is an important prerequisite to obtain accurate data.In recent years,this has also been a prevailing research field in order to expand the application of mass spectrometry.In the present work,based on systematic reviews of previous research and development trends of pretreatment technique for whole-rock and in-situ ICP-MS analyses,two devices were designed and developed:1)A multifunctional reagent purification system,which conquers the limitations of the existing sample preparation processes and the purification techniques for NH₄HF₂ and NH₄F,both of which are efficient digestion reagents used in earth science;2)A soft laser ablation cell,which breaks through the limitations of the sample size and shape by the traditional laser ablation cell,and makes in-situ analyses for large unbreakable samples by LA-ICP-MS possible.1.A multifunctional reagent purification system was designed and developed to efficiently purify NH₄HF₂ and NH₄F.The multifunctional reagent purification system presented here adopts a totally enclosed integrated design and consists of six main parts:a condenser,a purifier,a collection bottle,a waste liquid processor,a numerical control device,and a purge hood.The whole purification processes include three steps:1)The reagent to be purified is heated to sub-boiling state,which is regulated by the numerical temperature control device;2)The produced pure reagent steam is cooled and liquified in the condenser,and then is recovered in the collection bottle;3)The waste liquid is recovered to the waste liquid processor.All parts of the equipment that come into contact with the reagents are made of PFA or PTFE,which have excellent chemical stability.The heater is built inside the equipment,and no metal parts can be seen from outside.There is an automatic protection design for less acid or higher temperature than expected.The purification process is airtight and free from environmental pollution.Cooling water is not needed.The device presented here can not only purify solid NH₄HF₂ and NH₄F,but also can purify common chemical laboratory reagents,such as liquid nitric acid,hydrochloric acid,hydrofluoric acid and water.Solid-state NH₄HF₂ and NH₄F are two new kinds of"green geological sample digestion reagents"with superior digestion capacity,and both can be purified by this multifunctional reagent purification system.The solid NH₄HF₂ and NH₄F are distilled in a sub-boiling state,the speed of which is controlled according to the principle of sub-boiling distillation phase equilibrium.Then,the steam cools down automatically and crystallize to remove the original impurities.The rates for purifying NH₄HF₂ and NH₄F are 25-40 g/h and for liquid nitric acid,hydrochloric acid,hydrofluoric acid and water,the rates are 20-35 ml/h.The purified NH₄HF₂ has a background level of 0.001-0.8 ngg^-1for Li,Be,Cr,Co,Ni,Cu,Zn,Rb,Zr,Ag,Ba,Hf and Pb.The background values of Cr and Ni,which have the highest contents among all elements,decreased from 23.23 ngg^-1and 7.847 ng g^-1 before distillation,to 0.280 ng g^-1 and 0.073 ng g^-1 after purification,respectively,and the background values decreased by 80-fold and 100-fold,respectively.Using purified NH₄HF₂ and NH₄F to digest BHVO-2,BCR-2,AGV-2,GSP-2,G-2 and other international reference materials,the deviations of measured values from the recommended values are within 10%.The qualification rate for our data is 100%in the GeoPT proficiency testing program.The NH₄HF₂ and NH₄F purified by this system can be used as super pure digestion reagents.The purification system and the method for purifying NH₄HF₂ and NH₄F presented in this work play an important role in advancing the efficient pretreatment technology for geological samples.2.A soft laser ablation cell that can accommodate samples with variable shapes and volumes was designed and developed,and a preliminary experimental method for the direct and nondestructive in-situ analyses of large samples was established.The soft laser ablation cell consists of four parts:an observation window,a local extraction device,an outer cavity of TP flexible sample cell and a base.The sample is placed in the base of the cell.The transparent and flexible outer cavity is adjusted so that the area to be measured of the sample falls on the optimal ablation spot under the observation window.The optimal focusing distance is adjusted according to the height of the outlet of the local extraction device.Using the same instrument parameters,the international standard NIST610 was analyzed in the standard ablation cell of the GeoLas2005 system and in our soft ablation cell,respectively.The 32?m laser beam spot and 10 Hz ablation frequency were used to continuously ablate for 40s.The washout time was 18s and 1s,respectively.The washout time of the soft cell is about 94%faster than that of the standard ablation cell,the signal intensity is increased by 6%-30%,and the aerosol's transmission efficiency is 18 times that of the standard ablation cell.The shortest washout time obtained by the soft cell was only about 750 ms.The signal intensities of the international standard NIST612 obtained in six different three-dimensional positions were consistent,and the RSD was less than 3.21%.Two types of large samples,a blue-and-white porcelain pot and a stalagmite,were selected and in-situ analyzed using the soft cell as case studies.The results show that the distributions of elements such as Al,K,Co,Na,Pb,Mn,and Fe in the analysis spot of the blue and white porcelain are consistent with the element distributions of blue patterns in the region,and the results of trace elements in stalagmite are also in good agreement with the previous reported data.Compared to the fixed-form standard small-size ablation cell,a new type of flexible TP synthetic material was used,for the first time,to mold the outer cavity of the soft cell,allowing it to accommodate irregular samples with different shapes and volumes.The design of the local extraction device ensures efficient aerosol transport,extremely short washout time,and stable three-dimensional spatial reproducibility.Soft cell provides an important technology for in-situ analyses of large non-destructive samples and expands the application of LA-ICP-MS.