Research Of Absolute Determination Of Isotopic Abundance Using Multiple-Collector Inductively Coupled Plasma Mass Spectrometry And Determination Of Samarium Atomic Weight

Absolute determination of mass spectrometry, also called corrected determination of mass spectrometry, is a high precision and high accuracy method. After purification and quantitative dissolved, two concentrated isotope are blended to prepare synthetical isotope samples (isotope standards) by gravimetry using exact balance. According to measurement of isotope standards by mass spectrometry, the correction factor of system error can be confirmed. So the results of samples are corrected and measurement accuracy is ensured. The method is accepted by IUPAC to obtain isotopic abundance of unknown sample. In determination of atomic weight and isotope certified reference materials preparation, isotopic abundance almost is determined by this method. Typical instrument is thermal ionization mass spectrometry (TIMS).In this work determination of neodymium isotopic abundance by TIMS were studied. Sample loading and instrumental parameters were adjusted to optimization. Research of neodymium isotopic abundance measurement provides experimental and technical support of determination of neodymium atomic weight.Isobaric impurities must be removed before measurement because they will interfere the accuracy of results. In order to gain high chemical purity isotopes, separation process with P507 extraction resin of 200-300 meshes was used to remove rare earth elements impurities in neodymium and oxalate precipitation was used to determine the total content. All impurities of rare earth elements are less than 20ppm and the recoverability of neodymium is 93%.Multiple collectors inductively coupled plasma mass spectrometry (MC-ICP/MS) is a new type mass spectrometry for isotopic measurement. Its precision can be comparative to TIMS, but accuracy is not good because of more interferences. Optimum concentration, sampling position, nebulizer gas flow rate, collision gas flow rate and ion lens system were researched. The precision of isotopic ratio can be better than 0.01%. Concentrated isotope 152Sm and l54Sm were blended by gravimetry to prepare isotope standards. System error of MC-ICP/MS was corrected and absolute determination of MC-ICP/MS was established. Comparing with TIMS, the results of main isotopic ratio 154Srn/152Sm is better than 0.03%.According to this method, atomic weight of samarium was determined by MC-ICP/MS. The value is 150.3610?.0036. Comparing with the value 150.3600 determined by TIMS, the deviation is only 0.001%. This agreement shows that the method is available to complete the determination of atomic weight. It has advantages of simple pre-treatment, small sampling and rapid measurement. The research work provides a new optional method for value of isotope certified reference materials and develop the application of MC-ICP/MS.In order to conform to international standards and to ensure the quality of analysis work, a mathematical model was established for the uncertainty evaluation. This paper evaluated the uncertainty of the testing result, provided with the collection of all the parameters and the calculation methods needed for the calculation process, and evaluated the values of standard uncertainty, combined standard uncertainty, degrees of freedom and expanded uncertainty.