Copper sulphate as alternative to mercury monoxide catalyst in the Kjeldahl reaction
The Kjeldahl reaction developed to analyse nitrogen content of organic substances has been reviewed many times to optimize it and make safer for the users. A comprehensive handbook on various Kjeldahl analyses includes a chapter on catalysts that presents alternatives to mercury monoxide.
Mercury monoxide is not included in the EU harmonized classification. It is self classified as very toxic for aquatic environment, and toxic to humans (mercury itself being classified EU reprotoxic 1B).
Copper sulphate is classified as harmful if swallowed, skin and eye irritant and very toxic to aquatic environment.
Kjeldahl reaction, very used in studying protein content in organic matter, initially used mercury monoxide to catalyse sample digestion. Awareness on the hazards for health and environment as well as some process drawbacks lead to the substitution of mercuric monoxide (mercuric oxide). Copper and selenium compounds or their combinations and more recently titanium catalysts are considered safer alternative, with copper sulphate currently being the most commonly used.
The handbook containing information on catalyst properties notes that the alternatives give good results, even if the reaction time might be slightly longer than for mercury.
Other practical data on the various application of the Kjeldahl reaction and how to carry on different steps of the analysis are presented in the handbook.
The substitution eliminates the use of a mercury compound that is fatal by inhalation, ingestion and skin contact and that has negative impact on the environment. Since the alternative is hazardous to the aquatic environment, protective measures need to be taken.
Selenium reaction mixture (see Further information)
Alternative analytic methods ( see Further information)Further information
– Mercury monoxide MSDS from Sigma Aldrich
– Selenium reaction mixture MSDS from Sigma Aldrich
– Alternative method :
Type of information supplier
Producer / distributor
FOSS, DK-3400 Hilleroed, Denmark, www.foss.dk
The description is based on the document ’Handbook for Kjeldahl Digestion A recent review of the classical method with improvements developed by FOSS’ , published by FOSS, DK-3400 Hilleroed, Denmark , on its website, in 2008.Type of publication and availability
Internet brochure, freely available
Original document: click here
Publication or last update: January 2013