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The Schöniger digestion is a chemical process for the microanalytical detection of halogens and sulfur . It is named after its inventor, Wolfgang Schöniger . "The substance to be examined is burned in a piece of ash-free filter paper in a 500 ml oxygen-filled Erlenmeyer flask with standard ground joint NS 29/32, the combustion products are absorbed and the content of the element to be determined is measured by mass analysis."

principle

Possible folding of the filter paper for Schöniger digestion (brown = sample)
Schematic representation of the steps involved in the Schöniger digestion

Before the actual determination of the halogen, it must first be converted from its organic bond into an inorganic form by combustion. A small amount (typically a few milligrams up to about 100 milligrams) of the substance to be analyzed is therefore weighed out onto an ash-free filter paper. This paper is then folded up several times so that no analysis substance is lost and a short “ignition strip” protrudes. The folded paper is then placed in an open holding device made of platinum , which is connected to a ground-glass stopper via a longer wire and mesh.

Part of the Schöniger flask is filled with an absorption solution ( caustic soda or caustic soda with hydrogen peroxide ) and then thoroughly flushed with oxygen . After lighting a corner of the paper, it is quickly introduced into the oxygen atmosphere and the flask is tightly sealed with the stopper. Initially, the combustion creates a slight overpressure in the piston. To prevent the reaction gases from escaping, the flask can be turned upside down so that the absorption solution seals the stopper.

After complete combustion, the absorption of the combustion gases creates a vacuum in the piston. The flask is now shaken well to ensure that it is absorbed as quickly and completely as possible. The proportion of halogens in the solution can be determined, for example, via titration or chromatographic methods.

Applications

  • DIN 51400-3 - Testing of mineral oils and fuels - Determination of the sulfur content (total sulfur) - Part 3: Combustion according to Schöniger; Thorin sulfonazo III titration
  • DIN EN 14582 - Characterization of waste - Halogen and sulfur content - Oxygen combustion in closed systems and determination methods

literature

Web links

  • Juliane Maderegger: Insights in analytical chemistry. University of Bayreuth, September 20, 2010, accessed on February 28, 2011 (digestion of organic compounds by incineration).
  • Kurt Paulus: The "beautiful piston". Virtual Museum of Science, accessed on February 28, 2011 (images of various prototypes designed by Wolfgang Schöniger).

Individual evidence

  1. ↑ Wolfgang Schöniger: A microanalytical rapid determination of halogens and sulfur in organic substances , 1956.
  2. ↑ a b c Georg Schwedt and Joachim Schreiber: Pocket Atlas of Analytics . 3. Edition. Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2007, ISBN 978-3-527-31729-5 , sample preparation, p. 26-27 . ( limited preview in Google Book search).