Determination of Eu concentrations in coal, fly ash and sedimentary rocks using a cation exchange resin and inductively coupled plasma mass spectrometry (ICP-MS)

Europium (Eu) in coal, coal combustion residues (e.g., fly ash), and sedimentary rocks in coal-bearing sequences has attracted much attention in recent years mainly because of its world-wide demand and use as a geochemical indicator of geological setting for coal deposit studies. This paper presents a method for accurately measuring the concentration of Eu in coal, fly ash, and sedimentary rocks by quadrupole-based inductively coupled plasma mass spectrometry (ICP-MS), plus the use of closed-vessel microwave digestion and a cation exchange resin. To significantly diminish the inference of Ba-based polyatomic ions (137Ba16O, 136Ba17O, 135Ba18O, and 134Ba18OH) on 153Eu in coal, fly ash, and sedimentary rock samples, a Bio-Rad AG50W-x8 cation exchange resin was used to separate Ba from digested solutions of solid samples. The AG50W-x8 cation exchange resin can effectively separate the barium from digested solutions and thus could diminish the inference of Ba on Eu. The determination of Ba and Eu in the National Institute of Standards Technology (NIST) standard references of coal and fly ash samples showed that the use of the AG50W-x8 cation exchange resin combined with quadrupole-based ICP-MS analysis can provide a reliable method for the accurate determination of Eu concentrations in coal and coal-related samples. The method detection limits for Ba and Eu are 0.030 μg/l and 0.006 μg/l, respectively, and the determination coefficient of their calibration curves (linearity range 0-100 μg/l) is >0.9999. A Ba/Eu value of 1000 in the samples is proposed for judging the interference of Ba on Eu. If Ba/Eu > 1000, then Ba in coal, fly ash, and sedimentary rocks significantly interferes with Eu and this interference then needs to be considered when interpreting the analytical results and their significance.