The atomic absorption spectrometry method involves the use of sodium borohydride to generate arsenic hydrides, and their introduction into a silica furnace, maintained at dull red heat by the air—acetylene flame of an atomic absorption spectrophotometer. Atsuya and Akatsuka have described a method for determining trace amounts of arsenic. Jahns et al. have described a thin-layer chromatographic method for the determination of lead in sewage sludge, based on the use of ammonium pyrrolidinedithiocarbamate for the extraction and enrichment of lead. Accurate analysis was then performed after addition of varying quantities of metal standards and dilution to a standard volume according to the method of standard additions. Matrix interference in the determination of heavy metals in sludges by electrothermal atomic absorption spectrometry was particularly severe with regard to lead, cadmium and nickel determinations. Hydrofluoric acid had to be eliminated by evaporation and perchloric acid was a serious interferent.