Instrumental Isotopic Fractionation

Abstract

In mass spectrometry, the term ‘instrumental isotopic fractionation’ is recommended to describe the sum of the effects in a mass spectrometer occurring during sample introduction, ion formation, ion extraction, ion separation and ion detection leading to a difference of the measured isotope ratio from the true isotope ratio in a sample. Instrumental isotopic fractionation (IIF) describes the instrumental fractionation between nuclides of the same element resulting in erroneous results of isotope ratios. The major aspects of IIF for the different techniques (i.e. (LA)-ICP-MS, GDMS, TIMS, SIMS and IRMS) based on magnetic sector field analysers are presented. A special focus is set on the description of the major causes of IIF, the areas of occurrence in the respective instrumentations as well as the impact of IIF on the final measurement result and the related measurement uncertainty. The described techniques differ strongly in the extent of IIF, mainly due to the different ionization sources as well as vacuum conditions.

Performance of second generation ICP-TOFMS for (multi-)isotope ratio analysis: a case study on B, Sr and Pb and their isotope fractionation behavior during the measurements

“…Throughout the present study, measurement precision under different specied conditions of measurement are considered: 45 (i) isotope ratio precision (aka internal precision), expressed as RSD, refers to the standard deviation of M runs averaged to one measurement result, (ii) repeatability is the standard deviation of N measurements taken within a short time period, and (iii) intermediate precision is the standard deviation of N measurements over several days and used here as a measure for long-term stability.…”

“…35,37 This external IIF correction model can correct for mass dependent and mass independent IIF. 35 Taking a closer look at IIF, 34,41 previous studies using the rst generation of ICP-TOFMS reported that the IIF per mass unit is substantial for light elements (e.g., Li has −13%) whereas for high mass elements the IIF per mass unit is signicantly lower (e.g., Pb has 0.2%). 24 This is similar to observations from MC ICP-MS and ICP-QMS measurements, where the IIF typically varies systematically from about −13% to −15% for Li to −0.2% for U.…”

“…17,34 This phenomenon is referred to as instrumental isotopic fractionation (IIF, aka mass bias, mass discrimination) and has to be corrected for. 34 IIF includes all discrimination effects, and it is mainly determined by mass dependent effects but mass independent fractionation has also been observed for ICP-MS. The potential occurrence of mass independent IIF has signicant impact on the choice of the IIF correction model to determine reliable isotope ratios.…”

Application of non-traditional stable isotopes in analytical ecogeochemistry assessed by MC ICP-MS - A critical review

“…In ICP-MS, the ionization source and the interface are believed to play a major role in IIF, mainly due to the large pressure drop between the ion source and the expansion region. These phenomena have recently been described in more detail for ICP-MS, GDMS, TIMS, SIMS and IRMS [17].…”

“…Today, MC ICP-MS allows determining isotope ratios with measurement precisions comparable to those of TIMS (down to 0.001%) [10]. This might include preparatory work to fully separate the analyte isotopes from the matrix in order to overcome systematic errors derived from matrix-induced interferences as well as changes in instrumental isotopic fractionation (aka mass bias), which is significantly larger for MC ICP-MS [14][15][16] than for TIMS [12,17,18].…”