ION CHROMATOGRAPHIC STUDY OF THE EFFECT OF AMMONIUM-NITRATE AS A MODIFIER IN ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

Ammonium nitrate can be used as a chemical modifier in the determination of volatile elements by electrothermal atomic absorption spectrometry. It reacts with sodium chloride to produce ammonium chloride and ammonium nitrate, both of which are volatilized or decompose at temperatures below 400-degrees-C. The effectiveness of the reaction has been studied by ion chromatography to analyse solutions of salt residues remaining on a pyrolytic graphite platform heated to different char temperatures. Determination of ammonium, chloride, nitrate, nitrite and sodium in the solutions allowed losses of the ions during the char step to be monitored. In the absence of ammonium nitrate, losses of sodium and chloride began about 700-degrees-C and were complete by 1100-degrees-C. Addition of 300-mu-g of ammonium nitrate to 100-mu-g of sodium chloride caused an 85-90% loss of chloride from the platform at 200-degrees-C. Complete removal of chloride was not achieved until a temperature of 1000-degrees-C was achieved. Removal of chloride was accompanied by almost total loss of ammonium and partial loss of nitrate at 200-degrees-C. From 200 to 600-degrees-C, a more gradual loss of the remaining nitrate occurred and the production of nitrite was observed in the range 300-700-degrees. In the presence of ammonium nitrate, loss of sodium was noted at 800-degrees-C, and was almost complete by 1100-degrees-C.