Total reflection x‐ray fluorescence analysis of trace elements in highly saline samples

Abstract

The reliable trace analysis of high‐purity chemicals and environmentally relevant samples is more important than ever and has led to the development of novel analytical methods. Total reflection x‐ray fluorescence (TXRF) analysis is an increasingly known method for the determination of heavy metals at low concentration levels in environmental and industrial sample systems. However, there is still a need for optimization to obtain fast and precise results, especially for highly saline samples like brines and salts used in battery production or sea water. In this study, multi‐element standard solutions containing analytes like Co, Cr, Cu, Fe, Mn, Ni, or Zn in a concentration range between 0.1 and 1 mg/L were analyzed in the matrices lithium carbonate (Li2CO3) and artificial seawater (ASW) containing 1000 mg/L Li and 24,000 mg/L NaCl, respectively, leading to matrix‐analyte ratios of up to 240,000:1. Different sample preparation methods were compared in order to achieve the highest possible repeatability (1) and signal‐to‐noise ratios (2) with the least amount of time (3). Various parameters such as sample volume, drying conditions, time, temperature and additive concentration were varied. The relative standard deviation (RSD%) was used as a measure of repeatability for three replicates per sample. For lithium carbonate, a method with a preparation time of only 2 min and a measurement time of 500 s could be developed, which allowed to obtain RSD% well below 5%, a high linearity (R2 > 0.99) and limits of detection (LOD) in the range of 30 μg/L to 60 μg/L for most elements. Seawater analysis could be optimized with respect to signal‐to‐noise ratio, whereby the Kα‐line of the internal standard (Ga) was used for evaluation and the use of a desiccator was found to yield the best results.