Accurate and precise determination of isotopic ratios by MC‐ICP‐MS: A review

Abstract

For many decades the accurate and precise determination of isotope ratios has remained a very strong interest to many researchers due to its important applications in earth, environmental, biological, archeological, and medical sciences. Traditionally, thermal ionization mass spectrometry (TIMS) has been the technique of choice for achieving the highest accuracy and precision. However, recent developments in multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) have brought a new dimension to this field. In addition to its simple and robust sample introduction, high sample throughput, and high mass resolution, the flat-topped peaks generated by this technique provide for accurate and precise determination of isotope ratios with precision reaching 0.001%, comparable to that achieved with TIMS. These features, in combination with the ability of the ICP source to ionize nearly all elements in the periodic table, have resulted in an increased use of MC-ICP-MS for such measurements in various sample matrices. To determine accurate and precise isotope ratios with MC-ICP-MS, utmost care must be exercised during sample preparation, optimization of the instrument, and mass bias corrections. Unfortunately, there are inconsistencies and errors evident in many MC-ICP-MS publications, including errors in mass bias correction models. This review examines "state-of-the-art" methodologies presented in the literature for achievement of precise and accurate determinations of isotope ratios by MC-ICP-MS. Some general rules for such accurate and precise measurements are suggested, and calculations of combined uncertainty of the data using a few common mass bias correction models are outlined.

Accurate and Precise Determination of Silver Isotope Fractionation in Environmental Samples by Multicollector-ICPMS

“…used in previous studies [21][22][23][24] is both unnecessary and incorrect 20,25 . Thus, a mass bias correction approach based on internal normalization with Pd in combination with standard-sample-standard bracketing used previously for Ag isotope ratio determination in commercial products 20 was adopted here.…”

“…As detailed in a recent review 25 , for accurate and precise isotope ratio determination it is essential to correct for mass discrimination observed in MC-ICP-MS. It is a common practice to use internal standard for mass bias correction of analyte isotope ratios.…”

Resolving the Germanium Atomic Weight Disparity Using Multicollector ICPMS

“…11 Recent developments in MC-ICP-MS has brought a new dimension to this field. In addition to its simple and robust sample introduction, high sample throughput and high mass resolution, the relative precision of the isotope ratio measurements can be as low as ten parts per million, which is comparable to TIMS.…”

Observations of Large Mass-Independent Fractionation Occurring in MC-ICPMS: Implications for Determination of Accurate Isotope Amount Ratios

“…Many massbias correction models were initially developed for use with TIMS systems. 7 The Russell mass-bias correction model, eq 1, remains the most popular:…”

“…When MC-ICPMS became commercially available in the 1990s, this correction model was adapted and has since become a standard curriculum. 7 Owing to the empirical nature of the Russell's model, many other mathematical expressions are in widespread use. These can be expressed in the following generalized power-law expression: 8…”