Measurement of labile Cu in soil using stable isotope dilution and isotope ratio analysis by ICP-MS

Abstract

Isotope dilution is a useful technique to measure the labile metal pool, which is the amount of metal in soil in rapid equilibrium with the soil solution. This is normally performed by equilibrating soil with a metal isotope, and sampling the labile metal pool using an extraction (E value), or by growing plants (L value). For Cu, this procedure is problematic for E values, and impossible for L values, owing to the short half-life of the 64Cu radioisotope (12.4 h), which makes access and handling very difficult. We therefore developed an E value technique using enriched 65Cu stable isotope and measurement of 63Cu/65Cu ratios by inductively-coupled plasma mass spectrometry (ICP-MS) to measure labile pools of Cu in soils [1]. The 65Cu E values were compared to those determined using radioactive 64Cu.