Interference of aluminum chloride and nitrate on alkaline earth elements in an air-acetylene flame

Aluminum nitrate causes a strong interference in the determination of alkaline earth elements in the air-acetylene flame by formation of mixed oxides, predominantly of the spinel-type M^IIAl₂O₄. The influence of aluminum chloride is less pronounced because the analyte chloride must be converted to the oxide before it reacts with aluminum oxide. Any compound that delays the formation of oxides hence alleviates the depressing effect of aluminum. Particle size plays a decisive role in the sensitive equilibrium between alkaline earth chloride and oxide formation. Aluminum chloride hexahydrate hydrolyzes on desolvation in the flame, giving off HCl. This way an atmosphere of HCl is generated inside larger particles that isolate the analyte from oxygen in the flame gases and favor formation of thermally less stable chlorides, and hence atomization. Addition of an excess of cesium chloride increases the average particle size further and supports that mechanism. Moreover, cesium chloride causes an early disintegration of large particles releasing analyte chlorides into the flame, thus enhancing their degree of atomization.