Some Observations on Perchloric Acid Interferences in Furnace Atomic Absorption

Abstract

Many digestion and dissolution procedures produce a sample solution several tenths molar in perchloric acid. This amount of acid suppresses the furnace atomic absorption signal for many elements. The group 3A elements are particularly severely suppressed. 0.5 M HClO₄ causing over 95% reduction in peak absorbance for Al, Ga, and Tl, The effect persists even though the furnace tube is heated far above the HClO₄ boiling point during the ashing portion of the furnace cycle. Heating to about 1700°C is required to completely remove the residual effect. The analyte is vaporized at the proper stage in the furnace cycle but escapes in molecular form rather than being atomized. Perchloric acid or one of its decomposition products apparently interacts with the graphite to form a thermally stable product which later decomposes and inhibits atomization. The suppression can be reversed by addition of certain organic compounds such as sucrose or formic acid or by addition of excess ammonium carbonate or ammonium sulfate.