硼硅酸盐矿物硼的化学分离纯化与同位素测定方法

Improvement on Extraction and Determination Procedures of Boron Isotopic Composition in Tourmalines

采用碱熔法分解电气石样品,研究了3种不同纯化分离方法对硼回收和同位素测定的影响。实验表明:电气石中富含的Fe^(3+)和Al^(3+)对甲亚胺-H酸分光光度法测定硼含量有较大干扰,并在硼特效树脂交换分离中形成氢氧化物沉淀,阻塞交换柱;同时吸附溶液中硼元素造成回收率降低。本实验依次采用阴/阳离子混合树脂,硼特效树脂和阴/阳离子混合树脂三步离子交换进行电气石样品的纯化分离方法,实现了复杂基体中硼的完全回收(回收率99%)。在TIMS(Triton TI)采用H3和H4法拉第杯,并通过优化Zoom Optics参数(Focus Quad:15;Dispersion Quad:-85)实现静态双接收硼同位素组成测定。本方法对NIST SRM 951标准样品测定结果为^(11)B/^(10)B=4.05044±0.00012(2σ,n=8,1μg B),测定内外精度优于传统的动态峰跳扫。NIST SRM951测定结果为-0.3‰,表明预处理过程中无硼同位素分馏效应。天然样品硼同位素组成分别采用静态多接收PTIMS-Cs_2BO_2^+法和MC-ICP-MS测定,数据点基本分布在1:1线上,说明MC-ICP-MS测定结果与PTIMS方法结果相一致。

Tourmaline was decomposed by using alkali fusion,and then separated and purified by three different procedures.It is found that both Fe^（3＋） and Al^（3＋） ions that are rich in tourmaline samples seriously affect the accurate determination of boron concentration by azomethine-H spectrophotometric method and also cause the loss of boron by specific adsorption when large amount of amorphous hydroxide precipitate formed in ion exchange columns.The addition of small amount of EDTA can eliminate the influence,but brings serious isobaric interference on boron isotopic analysis by TIMS. Finally,we establish a three-column ion-exchange procedure including the first mixed resin column, the peristaltic pump coupled boron specific resin column,and the second mixed resin column,which ensures the full recovery of boron（about 99%） from tourmaline samples with complex matrices.The positive thermal ionization mass spectrometry（PTIMS）-Cs_2BO_2~＋ -static double-collection method was established by selecting H3-H4 Faraday cups and optimizing parameters in Zoom Optics（Focus Quad：15;Dispersion Quad：-85） in a Triton TI mass spectrometer.The determined average ^（11）B/^（10）B value of NIST SRM 951 is ^（11）B/^（10）B=4.05044±0.00012（2σ,n = 8,1μg B）,which is superior to the dynamic collection method in internal/external precision.Aδ^（11） B value of -0.3%o for NIST SRM 951 through the same pretreatment procedure was obtained,indicating that there was no isotopic fractionation occurred during the extraction procedure.The comparison of boron isotopes in natural samples by TIMS and MC-ICP-MS after chemistry procedure turns out that S＂B values determined by the PTIMS-Cs_2BO_2~＋ method are in good agreement with that by MC-ICP-MS.