What catalyst is best for digesting samples: copper or mercury?
Mercury (mercuric oxide) has been found to be the most effective catalyst for digesting nitrogen, but it is also an element of considerable environmental concern. Copper (copper sulfate) is suitable for a wide variety of samples and it has become the catalyst of choice in recent years. To test completeness of digestion, it is recommended to determine nitrogen recovery from samples that have been fortified (spiked) with nicotinic acid. Ammonium chloride is usually used as a fortifying (spiking) solution to test for loss of nitrogen during the digestion.
