Use of a Cu-selective resin for Cu preconcentration from seawater prior to its isotopic analysis by MC-ICP-MS

Abstract

Determination of the copper (Cu) isotopic composition (δ⁶⁵Cu) of seawater is difficult due to low Cu concentrations (0.3 to 7.6 nmol kg⁻¹) and high salt content. Here, we present a new procedure for matrix separation and Cu preconcentration based on a combination of a Cu-selective resin column and an AG MP-1M anion exchange resin column. The Cu-selective resin shows a quantitative recovery of 102.3 ± 5.0% (mean, 2SD, n = 5) and high selectivity for Cu over the main cations (Na, Mg, K and Ca) in seawater, efficiently preconcentrating Cu in seawater. Due to the hydrophobic nature of the Cu-selective resin, it was necessary to accelerate the preconcentration process using a peristaltic pump. Subsequently, an anion exchange resin was used to acquire a pure Cu fraction and thus ensure the accurate determination of seawater δ⁶⁵Cu. Seawater samples can be loaded on the Cu-selective resin column under a wide range of pH conditions (from pH = 4 to 9) instead of the narrow acidic pH range required in previous studies. The whole procedure is simple and has a low blank of 1.28 ± 0.48 ng Cu (n = 4). Results obtained from a series of doping experiments of seawater with an Alfa Cu standard confirmed the accuracy of the proposed method.