Determination of total chromium in terrestrial and marine samples by electrothermal atomic absorption spectrometry after pressure digestion

Abstract

A comparison between two commonly used sample digestion procedures was performed for the determination of total chromium in biological matrices. Ten reference materials (terrestrial and marine matrices) have been digested in HNO3, HNO3 + HClO4 and HNO3 + HF, respectively, under pressure in quartz vessels of a high pressure asher (HPA) or in PTFE bombs with external heating. Much lower chromium values than expected were obtained in most of the reference materials by using quartz vessels with nitric acid because of adsorption of chromium at quartz surfaces. Determinations after sample digestion in PTFE vessels with external heating showed expected results, except in some reference materials which precipitated more silica. An improvement of the results was observed by using a mixture of nitric acid and perchloric acid, but only the combination of nitric acid and a small amount of HF provided the desired results in all the reference materials studied.