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 mix ed oxides, predominantly of the spinel-type M(II)Al2O4. The influence of aluminum chloride is less pronounced because the analyte chloride m ust be converted to the oxide before it reacts with aluminum oxide. An y compound that delays the formation of oxides hence alleviates the de pressing effect of aluminum. Particle size plays a decisive role in th e sensitive equilibrium between alkaline earth chloride and oxide form ation. Aluminum chloride hexahydrate hydrolyzes on desolvation in the flame, giving off HCI. This way an atmosphere of HCI is generated insi de larger particles that isolate the analyte from oxygen in the flame gases and favor formation of thermally less stable chlorides, and henc e atomization. Addition of an excess of cesium chloride increases the average particle size further and supports that mechanism. Moreover, c esium chloride causes an early disintegration of large particles relea sing analyte chlorides into the flame, thus enhancing their degree of atomization.