硼酸溶液敞口酸溶-电感耦合等离子体质谱法测定萤石中稀土元素

Determination of Rare Earth Elements in Fluorite Samples by Open Boric Acid Dissolution and Inductively Coupled Plasma-Mass Spectrometry

萤石中稀土元素的研究对揭示成矿物质来源、成矿流体的性质和矿床成因均具有十分重要的意义。传统的过氧化钠碱熔一电感耦合等离子体质谱（ICP—MS）分析方法可以解决萤石中稀土元素的测定问题，但过氧化钠提纯难度高，过程繁杂，不宜大量样品的处理，且待测溶液总盐度大易产生基体干扰等；常规的酸溶法因使用的试剂一般为硝酸和氢氟酸，这些酸均不与萤石的主要成分氟化钙发生反应而很少应用。本文基于氟化钙能溶于硫酸和硼酸，采用硼酸溶液（10％硫酸和25％盐酸介质）和氢氟酸处理样品，硝酸提取，引入^103Rh和博^185Re双内标，建立了硼酸溶液敞口酸溶ICP—MS测定萤石中稀土元素的分析方法。相比于传统的过氧化钠碱熔方法，本方法采用的试剂纯度高，可以有效地降低空白，方法检出限为0．002～0．016μg／g，低于过氧化钠碱熔方法的检出限（0．006～0．058μg／g），回收率在94．0％～107．6％之间，方法精密度（RSD）为0．7％～2．7％。本方法配制的硼酸溶液能够有效地与萤石反应，可充分分解萤石样品，简化了样品处理流程，有效地控制了稀土元素的损失，数据可靠性高，适用于大量萤石样品的稀土元素分析。

The research of rare earth elements （REEs） in fluorite has very important significance for determining the source of ore-forming materials, the nature of ore-forming fluid and genesis. The determination of REEs in fluorite can be solved by Inductively Coupled Plasma-Mass Spectrometry （ICP-MS） with sodium peroxide fusion, but the sample handling process is complex; sodium peroxide is difficult to purify and matrix interferences derive from high salinity solution, making it unsuitable for processing large numbers of samples. Nitric acid and hydrofluoric acid, which are used for the conventional method, do not react with calcium fluoride, which can be dissolved in sulfuric acid and boric acid. To this end, a method for the determination of 15 rare earth elements in fluorite by ICP-MS has been developed. The fluorite samples were decomposed with boric acid solution （ media with 10% H2SO4 and 25% HC1） and hydrofluoric acid in PTFE beakers, and then dissolved with nitric acid. Two internal standards of 103 Rh and 185 Re were selected to compensate the drift of analytical signals and correct matrix effects by ICP-MS. Compared with the traditional sodium peroxide alkali fusion method, this method adopted the reagents of high purity which can reduce the background effectively. The detection limits were 0. 002 - 0. 016 ~g/g, which is lower than that by sodium peroxide fusion （0. 006 -0. 058 μg/g）, and the precisions were 0.7% -2. 7%. The results of this method were consistent with the results by sodium peroxide fusion. The new established method was is simple and had has a low detection limit for processing large numbers of fluorite samples.