In order to determine elements which are easily volatilized, or are present as volatile species, organic material may be ashed in oxygen in a closed oxygen combustion system. One such method is oxygen-flask combustion by which the test sample is burned in a closed flask containing oxygen and an absorbing solution in which the analytes are subsequently determined.
PAC, 1988, 60, 1461. 'Nomenclature, symbols, units and their usage in spectrochemical analysis-X. Preparation of materials for analytical atomic spectroscopy and other related techniques (Recommendations 1988)' on page 1468 (https://doi.org/10.1351/pac198860091461)