Evaluation of Partial Digestion as a Strategy for Elemental Analysis of Inorganic Samples by Inductively Coupled Plasma–Optical Emission Spectrometry (ICP OES)—A Proof of Concept Study

Abstract

This study discusses the application of microwave-assisted sample preparation for inorganic samples using concentrated or diluted HNO₃ solutions followed by determination of Al, Ca, Cu, Cr, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Si, and Zn using inductively coupled plasma–optical emission spectrometry (ICP OES). Aiming the total digestion (reference procedure), samples were decomposed in a heating block using a mixture of 2 mL of 40% v v⁻¹ HF and 5 mL of 14 mol L⁻¹ HNO₃. Four digestion mixtures composed by (1) 14, (2) 7.0, (3) 4.0, and (4) 2.0 mol L⁻¹ HNO₃ plus 3 mL of concentrated H₂O₂ were evaluated as alternatives for microwave-assisted digestion of six inorganic samples (partial digestion). Considering all evaluated procedures, quantitative recoveries were obtained applying reference and partial digestion procedures. Therefore, the use of HNO₃ dilute solutions as an alternative for HF is a feasible procedure for quantitative analysis of zinc oxide, kaolin, zinc residue, and zinc sulfide. However, tailored procedures must be taken into consideration, since quantitative determination depends on digestion mixture, sample matrix, and analytes.

Keywords:

• Inductively coupled plasma–optical emission spectrometry (ICP OES)
• inorganic samples
• microwave-assisted digestion
• partial digestion
• sample preparation

Conflicts of interest

There are no conflicts of interest to declare.

Additional information

Funding

The authors are grateful to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq,147727/2018-9, 141634/2017-0, 305201/2018-2 and 428558/2018-6) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES/PNPD – Graduate Program in Chemistry, Federal University of São Carlos). Instrumental support provided by Analítica (São Paulo, SP, Brazil), Milestone (Sorisole, Italy) and Thermo Scientific (São Paulo, SP, Brazil) is gratefully acknowledged. The authors also would like to express their gratitude to the Instituto Nacional de Ciências e Tecnologias Analíticas Avançadas – CNPq, Grant No. 573894/2008-6 and FAPESP, Grant No. 2014/50951-4.