Retardation of Surface Adsorption of Trace Metals by Competitive Complexation

Abstract

The storage of samples containing trace metals has resulted in the adsorption of certain metals onto the surface of the container. The effect of the adsorption of trace amounts of lead and cadmium on subsequent analyses using atomic absorption spectroscopy was studied. The effects on adsorption by factors such as pH, container composition, buffer composition, metal concentration, and storage time were studied. Significant adsorption of trace amounts of lead and cadmium occurred rapidly onto both Pyrex and polyethylene containers in alkaline solution. Minimization of this adsorptive interference was attempted through the use of organic chelating agents. EDTA and thenoyltrifluoroacetone were utilized to provide retardation of the adsorption via a competitive complexation for the metal ion with the container surface. The presence of thenoyltrifluoroacetone and EDTA, in the otherwise identical solutions, successfully prevented the adsorption onto the surface of the container over a wide range of pH. In addition, the EDTA was also capable of rapidly desorbing lead which had been adsorbed for as long as 40 days on Pyrex and polyethylene surfaces.