Aqua regia digestion

The aqua regia digestion is a digestion process in analytical chemistry that is used to digest mineral and soil samples. It can be described as a partial outcrop, as mineral oxides remain (e.g. sand ).

Mode of action

Aqua regia has different modes of action, which complement each other in the digestion and thus lead to an almost complete dissolution of the matrix. Only a few mineral oxides remain. Due to the high temperature (boiling) during digestion, the reactions take place in a reasonable time.

The chlorine radicals and nitrosyl chloride are strong oxidizing agents and attack organic substances and most metals.
The extremely low pH leads to the dissolution of many metal oxides and salts
The high concentration of chloride ions favors the solution of even poorly soluble oxides and passivated metals due to the formation of chloro complexes. (Basic) iron oxides react, for example, due to the excess of protons (H +) to form iron (III) ions and water. The iron ions in turn react with chloride ions to form a chloro complex. In this complex , the iron is masked and cannot be analyzed analytically without further processing (complexing effect).

After the actual digestion, it is repeated with conc. Fumed nitric acid to remove excess chlorine compounds. The almost dry residue is taken up with a dilute (approx. 5%) nitric acid and is thus available for many analysis methods.

Individual evidence

↑ Peter Kurzweil: Chemistry . 10th, revised edition. Springer Vieweg, Wiesbaden 2015, ISBN 978-3-658-08660-2 , p. 149 , doi : 10.1007 / 978-3-658-08660-2 .

[1] Peter Kurzweil: Chemistry . 10th, revised edition. Springer Vieweg, Wiesbaden 2015, ISBN 978-3-658-08660-2 , p. 149 , doi : 10.1007 / 978-3-658-08660-2 .