Assessment of Polyatomic Interferences Elimination Using a Collision Reaction Interface (CRI) for Inorganic Analysis of Fuel Ethanol by ICP-QMS

Abstract

The effectiveness of a collision-reaction interface (CRI) as instrumental device and the addition of oxygen in the composition of auxiliary gas were evaluated to minimize polyatomic species generated in plasma gas caused by direct introduction of fuel ethanol samples through spray chambers in inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). The oxygen flow-rate was optimized as a compromise among signal counts, signal to background ratio (SBR), and background equivalent concentration (BEC). For 12.5 mL min⁻¹ O₂, ethanol samples diluted 20 times were introduced into the plasma and deposits of carbon compounds on the sampler and/or skimmer cones were not observed. The performance of CRI using H₂ and He inserted through the sampler or skimmer cones was evaluated. Hydrogen gas added through the skimmer cone was more efficient to reduce blank and BEC values. This strategy was necessary to eliminate spectral interferences caused by ⁴⁰Ar¹²C⁺, ⁴⁰Ar¹⁶O⁺, ¹²C¹⁶O⁺, at isotopes ⁵²Cr⁺, ⁵⁶Fe⁺, ²⁸Si⁺ and ²⁴Mg⁺, respectively. Using matrix-matching calibration and Y internal standard, the optimized method was applied to the determination of Al, Ba, Co, Cr, Cu, Fe, Mg, Mn, Mo, Na, Ni, Pb, Sb, Si, V, and Zn in fuel ethanol. Accuracy of developed method was checked after addition/recovery tests. Recoveries and RSD (n = 12) for all elements varied within the 78–114% and 0.4–2% ranges, respectively. Limits of detection for all elements obtained by combining CRI and ICP-QMS were always better than 0.80 µg L⁻¹ except for Si at 14 µg L⁻¹.

Keywords:

• Collision-reaction interface
• Ethanol fuel
• ICP-QMS
• Polyatomic interference

Acknowledgments

Authors would like to thank the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for financially supporting this work (Grants 2006/59083-9 and 2010/17387-7). Authors are also grateful to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for fellowships to D.R.N. and R.S.A., and research grants to José A. Gomes Neto and J. A. Nóbrega.