Comparison of electrodeposition and precipitation for the preparation of samples for iodine analysis by AMS

Sample preparation for Accelerator Mass Spectrometry (AMS) analysis of ¹²⁹I from environmental samples typically involves isolation and purification of the iodine followed by precipitation as silver iodide. The silver iodide is mixed with silver or niobium powder as a binder and medium for electrical conductivity and approximately 3 mg of the mixture pressed into a cathode for AMS analysis. Electrodeposited silver iodide on a silver clad niobium 50 µm diameter wire provides an attractive alternative to precipitation. Six inches of wire and electrodeposited silver iodide are easier to handle when pressing cathodes and minimizes possible cross contamination between samples. Although electrodeposition onto pure silver wires has been recently reported, the usage of silver clad niobium wires could offer an additional advantage. The use of niobium in the silver iodide matrix has been reported to result in higher intensity and long term stability of the iodide ion current. This paper presents a comparison of electrodeposition methods using silver and silver clad niobium wires to the traditional precipitated silver iodide mixed with silver and niobium powders. The comparison was done using materials with ^129/127I ratios having nominal values of 5 × 10⁻¹⁰ and 5 × 10⁻¹¹. For each ^129/127I ratio material, eight samples were analyzed for each preparation method on three days, with seven replicate AMS measurements per sample. For each ratio, the measurements of the separate days were combined for each method, yielding 168 measurements per method. An analysis of variance indicated minor statistical differences between the precipitated and electro-deposited materials, with the pooled standard error of the means being 0.2% for both ∼5 × 10⁻¹⁰ and ∼5 × 10⁻¹¹ ratios.