Direct atomic spectrometric analysis by slurry atomisation. Part 2. Elimination of interferences in the determination of arsenic in whole coal by electrothermal atomisation atomic absorption spectrometry

Abstract

The analysis of whole powdered coal without sample dissolution has been investigated. Techniques have been established for the determination of arsenic by slurry injection into an electrothermal atomiser for atomic absorption spectrometry. The effects of the furnace programme, type of background correction, form of atomisation and slurry matrix have been investigated. Calibration was achieved using aqueous standards with sample distruction performed in situ in the furnace.

The coal was slurried in nickel nitrate (matrix modifier), magnesium nitrate (ashing aid), nitric acid and ethanol (wetting agent). The use of conventional continuum-source and Smith-Hieftje background correction systems was compared for correction of a broadened aluminium line interference at the most sensitive As line (193.7 nm). Only the latter was effective, because the interfering line is within the monochromator band pass. A carefully designed heating programme to separate temporarily the arsenic and aluminium absorption peaks was also advantageous. The less sensitive 197.2-nm line yielded comparable results with either form of background correction.

Complete recoveries of arsenic were achieved when the particle size was reduced to 30 µm. Samples could be injected from either constantly agitated slurries or thixotropically stabilised suspensions. A number of certified reference material coals were analysed (NBS SRM 1632a and 1635 and BCR No. 40). Excellent agreement was obtained between the results from the preferred slurry method and certificate value.