New approach for understanding the fundamental chemistry of the oxidative sample digestion in spectrochemical analysis

ABSTRACT

The process known as “wet digestion” is widely used in analytical chemistry as the most common way of dissolving solid samples for elemental spectrochemical analysis. Wet digestion involves the use of oxidizing reagents and acids–mainly HNO₃, H₂O₂, H₂SO₄, HClO₄, and other complementary acid reagents such as HF, HCl, or their mixtures. Wet digestion has become popular and attractive to users in part owing to the application of modern equipment with new technologies such as temperature-controlled heating blocks, microwave systems, and automated digestion systems, among others. Nonetheless, the use of modern, sophisticated instruments does not change the physical and chemical foundations of the classic chemical process. Until now, simplified equations have been used to explain this process. However, fundamental chemical mechanisms and thermodynamic concepts have been commonly left aside. In this work, the acid digestion of samples has been approached based on the chemical reactions, detailing the role and the effect of main reagents and intermediaries. The reactions that can occur during the digestion process have been specified considering the fundamental thermodynamic properties of the reagents used, especially the oxidizing reagents HNO₃ and H₂O₂. This article will be a beneficial resource for students, instructors, and professionals alike.

KEYWORDS:

• Fundamentals
• sample digestion
• HNO₃
• H₂O₂
• spectrochemical analysis
• tutorial

Acknowledgments

The authors thank the valuable contribution of Prof. Ramon M. Barnes for providing valuable comments about this manuscript.

Funding

The authors thank the support of the National Commission for Scientific and Technological Research (Conicyt) project Fondecyt N°1151296; Center Optics and Photonics, Grant CONICYT-PFB-0824 and CONICYT/FONDAP/15110019. Furthermore, the authors appreciate the support of the international collaboration program of project Fondecyt N°1151296 and Fulbright Specialist Program #7003 for the financial support of Professor Dulasiri Amarasiriwardena visit to the University of Concepción.