Determination of Calcium Isotopes Using Inductive Coupled Plasma-Tandem Mass Spectrometry with Ozone-Induced...

Area of Science:

• Analytical Chemistry
• Isotope Geochemistry
• Mass Spectrometry

Background:

• Calcium (Ca) isotope analysis using Inductively Coupled Plasma-Tandem Mass Spectrometry (ICP-MS/MS) is challenged by isobaric interference from Argon (Ar).
• The most abundant Ca isotope, ⁴⁰Ca, shares the same mass as ⁴⁰Ar, a common carrier gas in ICP-MS, significantly reducing detection sensitivity.
• Existing methods struggle to accurately quantify Ca isotopes in the presence of high Ar concentrations.

Purpose of the Study:

• To develop a novel ICP-MS/MS method for precise and sensitive determination of calcium isotopes.
• To mitigate the spectral interference caused by ⁴⁰Ar during ⁴⁰Ca measurements.
• To enable the detection of less abundant Ca isotopes (⁴³Ca, ⁴⁴Ca, ⁴⁶Ca, ⁴⁸Ca) with high sensitivity.

Main Methods:

• Utilized inductive coupled plasma-tandem mass spectrometry (ICP-MS/MS) for Ca isotope analysis.
• Introduced ozone (O₃) as a reaction gas within the collision cell to selectively react with Ca ions.
• Investigated the reaction mechanism of Ca⁺ with O₃ and Ar⁺ with O₃ using quantum chemistry calculations (density functional theory).

Main Results:

• The reaction of Ca⁺ with O₃ preferentially formed CaO₃⁺, effectively differentiating Ca from Ar.
• Argon ions (Ar⁺) reacted with O₃ to form ArO⁺ and subsequently Ar⁺, not ArO₃⁺, minimizing Ar interference.
• The developed method successfully detected low-abundance Ca isotopes (⁴³Ca, ⁴⁴Ca, ⁴⁶Ca, ⁴⁸Ca) in certified reference materials with high sensitivity.

Conclusions:

• The proposed ICP-MS/MS method using ozone effectively resolves the ⁴⁰Ar interference issue in Ca isotope determination.
• This technique significantly enhances the sensitivity and accuracy for measuring various calcium isotopes.
• The study provides a robust analytical approach for precise Ca isotope quantification in diverse sample matrices.