A combustion train is an analytical tool for the determination of elemental composition of a chemical compound. With knowledge of elemental composition a chemical formula can be derived. The combustion train allows the determination of carbon and hydrogen in a succession of steps:
* combustion of the sample at high temperatures with Copper(II) oxide as the oxidizing agent,
* collection of the resulting gas in a hygroscopic agent (magnesium perchlorate or calcium chloride) to trap generated water,
* collection of the remainder gas in a strong base (for instance potassium hydroxide) to trap generated carbon dioxide.
Analytical determination of the amounts of water and carbon dioxide produced from a known amount of sample gives the empirical formula. For every hydrogen atom in the compound 1/2 equivalent of water is produced, and for every carbon atom in the compound 1 equivalent of carbon dioxide is produced.
Nowadays, modern instruments are sufficiently automated to be able to do these analyses routinely. Samples required are also extremely small &mdash; 0.5 mg of sample can be sufficient to give satisfactory CHN analysis.