Ultratrace and precise isotope analysis by double-focusing sector field inductively coupled plasma mass spectrometry

Abstract

Double-focusing sector field inductively coupled plasma source mass spectrometry with its capability of providing a very sensitive multi-element analysis has been established for the determination of trace and ultratrace elements in high-purity materials, environmental samples and radioactive waste materials. Some applications of double-focusing sector field ICP-MS for the multi-element analysis of trace and ultratrace impurities in high-purity inorganic materials are described. A matrix separation procedure for ZrO₂ by liquid–liquid extraction after microwave-induced dissolution in an acid mixture is proposed in order to determine ultratrace impurities. The detection limits of ICP-MS reached after matrix separation in solid samples are in the low ng g^–1 concentration range. The detection limits in ICP-MS (determined by the blank values of the chemicals used) are comparable to those of solid-state mass spectrometry, which allows the direct determination of trace impurities in high-purity solids. Isotope ratio measurements of Mg, K and Ca were performed to investigate the transport phenomena of nutrient solutions in plants by tracer experiments using highly enriched ²⁵Mg, ²⁶Mg, ⁴¹K, ⁴²Ca and ⁴⁴Ca isotopes. In order to separate the ³⁸ArH⁺ and ⁴⁰ArH⁺ ions from the ³⁹K⁺ and ⁴¹K⁺analyte ions for potassium isotope ratio measurements, double-focusing sector field ICP-MS with an ultrasonic nebulizer was used at a mass resolution of 9000. The precision of potassium isotope ratio measurements was 0.7% (at a potassium concentration of 100 µg l^–1). Isotope ratios of Mg and Ca (each at a concentration of 50 µg l^–1) were determined at a mass resolution of 3000 with a precision of 0.4 and 0.5% on real biological samples. The accuracy of isotope ratio measurements of K and Mg was determined using isotopic standard reference materials with natural isotope composition (NBS SRM 985 and 980). The results of isotope ratio measurements of K, Mg and Ca on real biological samples doped with enriched stable isotopes are discussed.