Isobaric Spike Method for Absolute Isotopic Ratio Determination by MC-ICP-MS

Area of Science:

• Geochemistry
• Analytical Chemistry
• Isotope Analysis

Background:

• High-precision natural isotopic abundance data are often unavailable for elements with few isotopes or isobaric interferences.
• Accurate absolute isotope ratios are essential for isobaric interference corrections and spike calibrations in mass spectrometry.

Purpose of the Study:

• To develop a novel method for absolute isotope ratio analysis integrating the double-spike concept with isobaric element pair analysis.
• To determine absolute isotopic ratios for Ca, V, Cr, Ni, and In using multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS).

Main Methods:

• Integration of the double-spike method with isotopic analysis of element pairs sharing isobaric isotopes.
• Utilizing multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) to measure mixtures of sample and spike elements.
• Simultaneous measurement of Ti and Ca isotopes to establish a quantitative relationship between instrumental mass fractionation and element mass.

Main Results:

• Absolute isotopic ratios were successfully determined for Ca, V, Cr, Ni, and In with per mil level accuracy.
• A quantitative relationship between instrumental mass fractionation factors and elemental masses was established.
• Obtained absolute ratios show excellent agreement with existing literature data after instrumental mass fractionation correction.

Conclusions:

• The developed method effectively measures absolute isotope ratios for elements with isobaric interferences, addressing a critical data gap.
• This technique improves the accuracy of isobaric interference corrections, especially in challenging analytical scenarios like laser ablation.
• The established relationship between mass fractionation and elemental mass offers a valuable tool for advanced isotopic analysis.