Hydrogen compounds formation of calcium in an ICP-DRC-MS

Abstract

Isobaric ions overlap an isotope of interest in mass spectrometry, and an inductively coupled plasma-dynamic reaction cell-mass spectrometry (ICP-DRC-MS) analysis also bears the same problem. In this research, processes of ⁴⁰CaH⁺ formation and decreasing methods were studied. Plasma power was swept from 1300 W to 600 W to investigate ⁴⁰CaH⁺ formation in the plasma. 1.90 × 10⁻⁴ of ⁴⁰CaH⁺/⁴⁰Ca⁺ with 1300 W decreased to 1.27 × 10⁻⁴ when 750 W of plasma power was applied. Deionized water of samples was replaced with heavy water to verify if ⁴⁰CaH⁺ is formed in the interface part of the equipment. Normally NH₃ gas is injected into the DRC to remove argide ions for a measurement of calcium samples in an ICP-DRC-MS, but we found NH₃ contributes to form hydrogen compounds in the DRC by introducing a strontium sample, which is the same alkaline earth metal as calcium. 1.59 × 10⁻⁴ of ⁴⁰CaH⁺/⁴⁰Ca⁺ at 0.8 ml min⁻¹ of NH₃ cell gas decreased to 1.72 × 10⁻⁵ with 0.85 ml min⁻¹ of additional O₂cell gas injection. Results verify that hydrogen compounds made from NH₃ in an ICP-DRC-MS could affect ultra trace isotope ratio analysis.