Development of a high ratio isotope dilution mass spectrometry calibration technique for chemical metrology

Abstract

IDMS with calibration by ''exact'' or ''approximate signal matching'' methods offers a number of advantages for chemical metrology applications where measurements of low uncertainty are required for analytes at low concentrations in complex matrices. These methods have been applied extensively but are unsuitable for some important applications because in many cases, the concentration of the spike isotope in each measured blend of a sample or standard should be as close as possible to the concentration of the natural analyte isotope. In this paper we discuss recent work investigating the extent to which it is possible to move away from this ideal 1 : 1 blend isotope ratio whilst retaining the key benefits of the approximate matching technique. This has been used for the first time for applications where the sample has a very high analyte concentration, which would require unacceptably high amounts of spike with the existing method. The methodology has been validated for sulfur using a well-characterised candidate matrix reference material -NIST SRM1624d. This is a diesel fuel sample that contains approximately 4000 mg g À1 sulfur. Results were obtained using a ratio for 32 S/ 34 S of 14, achieving accuracy and uncertainty comparable with the original method using a blend isotope ratio of 1.

Validation of isotope dilution surface‐enhanced Raman scattering (IDSERS) as a higher order reference method for clinical measurands employing international comparison schemes

“…[6,7] Today, IDMS is the only accepted method to realize SI-traceable amount-of-substance measurements, and, thus, most national metrology institutes (NMIs) have built their national standards in analytical chemistry upon this technique. [8,9] From a metrological point of view, it is therefore desirable to have an alternative approach, which is based on a different physical principle. Tackling analytical problems with different measurement techniques allows the identification of hidden contributions to the measurement uncertainty and might generally improve the reliability of a comparison.…”

An Isotope Dilution ICP‐MS Method for the Determination of Mg/Ca and Sr/Ca Ratios in Calcium Carbonate

“…The isotopic ratios attained in this way for coral samples were: 24 Mg ⁄ 25 Mg $ 0.4, 48 Ca ⁄ 43 Ca $ 0.12 and 88 Sr ⁄ 87 Sr $ 1.2, close to the optimal ratios predicted by isotope dilution error equations of 0.34, 0.04 and 1 respectively. In the case of Ca, a ratio three times larger was used in order to minimise the use of this costly isotope, although this does not entail a significant deterioration of the method precision (Hearn et al 2005). Solutions were aspirated in aliquots of about 50 ll (for the lowest flow rate nebuliser), at least three times during the analysis sequence.…”

Determination of low‐level (sub‐microgram) sulfur concentrations by isotope dilution multi‐collector inductively couple plasma mass spectrometry using a 33S spike and internal normalization for mass bias correction

“…In recent years, inductively coupled plasma mass spectrometry (ICP‐MS) has been investigated as a means of measuring the sulfur amount of lower concentration materials . The main advantage of ICP‐MS techniques over ID‐TIMS is the elimination of the chemical reduction procedure needed for the latter technique.…”

“…ICP‐MS techniques generally require less sample processing and consequently are relatively free of chemical processing blank contributions. The use of ID‐ICP‐MS, whether employing a quadrupole ICP‐MS or a sector‐field instrument, has shown that lower blanks are achievable . However, corrections for instrumental and matrix‐induced mass bias are larger and more variable than those observed for TIMS.…”

“…Measurement of sulfur by quadrupole ICP‐MS are also complicated by the generation of interfering ions that cannot be resolved from the sulfur peaks of interest (Table ). High‐resolution sector field ICP‐MS instruments, in contrast, are capable of resolving many of these interferences when operated in medium resolution (3000) mode …”