Oxygen bomb combustion ion chromatography for elemental analysis of heteroatoms in fuel and wastes development

Abstract

An analytical procedure, oxygen bomb combustion ion chromatography (IC), was developed for the elemental analysis of heteroatoms in fuel and organic wastes. The use of oxygen bomb combustion under elevated oxygen pressure (25 atm) was shown to produce nitrate upon oxidation of atmospheric nitrogen. As the nitrate formed could affect bromide determination, three methods for removing atmospheric nitrogen using evacuation, rinsing and purging procedures were investigated and the best method found is the purging of air by passing oxygen gas at ambient pressure at a rate of 420 ml/min for 5 min which was shown to be able to remove 95% of the nitrates. The use of the more sensitive indirect photometric detection method was investigated for non-suppressed IC determination of anions using the phthalate mobile phase system. Good separation and satisfactory sensitivities were obtained for all the heteroatoms studied. In general, the oxygen bomb IC procedure was shown to give satisfactory results for heteroatom determination except nitrogen which show low recovery (< 50%) and poor repeatability (> 40% R.S.D.) as results of the formation of the insoluble NO and N2 during oxidation. Under the optimised conditions, linear working ranges up to 3 orders of magnitude, good repeatability of less than 2%, low detection limits at sub-μg/ml level, satisfactory retention times up to 16 min and good recoveries of more than 95% were obtained for the heteroatoms investigated. The optimised analytical parameters for the procedure developed for the analysis of fluoride, phosphorus, chloride, bromide, iodide and sulphur are given and discussed.