磁式电感耦合等离子体质谱仪及其在核地质分析中的典型应用

Inductively Coupled Plasma-Sector Field Mass Spectrometers and Typical Applications in Nuclear Geology

磁式电感耦合等离子体质谱(ICP-SFMS)主要包括高分辨等离子体质谱(HR-ICP-MS)、多接收等离子体质谱(MC-ICP-MS)和全谱等离子体质谱(Spectro-ICP-MS)。HR-ICP-MS一般采用反向Nier-Johnson结构磁-电双聚焦布置,MC-ICP-MS采用正向Nier-Johnson结构电-磁双聚焦布置,而采用检测器阵列的全谱磁式ICP-MS则采用Mattauch-Herzog结构布置。磁式电感耦合等离子体质谱仪性能改进主要体现在:调频ICP设计提高了对基体的耐受性及可靠性;采用J型采样锥和X型截取锥提高了灵敏度;大抽速接口泵可提高接口区真空度和仪器的灵敏度;改进的离子传输透镜系统可提高对锕系同位素的丰度灵敏度;改变接收器前的狭缝宽度可获得高分辨同位素比值;多个Daly检测器的使用可提高对低丰度同位素的检测能力;通过软件自动切换法拉第杯放大器高阻,能提高低丰度同位素测量的信号输出。磁式ICP-MS性能的改善,使其在核地质分析中的应用更广泛。使用激光烧蚀高分辨等离子体质谱(LA-HR-ICP-MS)可进行铀矿物微区原位U-Pb定年,使用MC-ICP-MS可高精密度地测定U同位素分馏,采用无熔剂制样LA-HR-ICP-MS可测定U、Th、Nb、Ta、Zr、Hf等难溶元素。

Inductively coupled plasma sector field mass spectrometers(ICP-SFMS)mainly include high-resolution ICP-MS(HR-ICP-MS),multi collector ICP-MS(MC-ICP-MS)and full spectrum ICP-MS.The HR-ICP-MS generally adopts the revise Nier-Johnson magnetic-electrostatic sectors double focusing geometry,the MC-ICP-MS generally adopts the forward Nier Johnson electrostatic-magnetic sectors double focusing geometry,and the full spectrum ICP-MS with detector array adopts the Mattauch-Herzog geometry.The performance improvement of ICP-SFMS is mainly reflected in the frequency turning ICP design,which improves the tolerance and reliability to the matrix,the J-type sampler cone and X-type skimmer cone are used to improve the sensitivity,the large pumping speed interface pump can reduce the vacuum in the interface area and improve the sensitivity of the instrument,and the improved ion transfer lens system can improve the abundance sensitivity of actinide isotopes.High resolution isotope ratio can be obtained by changing the slit width in front of the detectors.The use of multiple Daly detectors can improve the detection ability of low abundance isotopes.The signal output of low abundance isotope measurement can be improved by automatically switching the high resistance of Faraday cup amplifier through software.The improvement of the performance of ICP-SFMS makes it more widely used in nuclear geological analysis.In situ U-Pb dating of pitchblende micro area can be carried out by LA-HR-ICP-MS,uranium isotope fractionation can be determined with high precision by MC-ICP-MS,and refractory elements such as U,Th,Nb,Ta,Zr and Hf can be determined by LA-HR-ICP-MS.