Determination of Background Concentrations of Ag, Pd, Pt and Au in Highly Mineralized Ground Waters at Sub-ng L-1 Concentrations by Online Matrix Separation/Pre-Concentration Coupled to ICP-SFMS.

Lisa Fischer,Stephan Hann,Bernadette Moser

doi:10.3390/molecules26237253

Abstract

Though not regulated in directives such as the Water Framework Directive of the European Union, the investigation of geogenic background concentrations of certain elements such as precious metals is of increasing interest, in particular for the early detection of a potential environmental pollution due to the increased use in various industrial and technological applications and in medicine. However, the precise and accurate quantification of precious metals in natural waters is challenging due to the complex matrices and the ultra-low concentrations in the (sub-) ng L−1 range. A methodological approach, based on matrix separation and pre-concentration on the strong anion exchange resin TEVA® Resin in an online mode directly coupled to ICP-SFMS, has been developed for the determination of Ag, Pt, Pd and Au in ground water. Membrane desolvation sample introduction was used to reduce oxide-based spectral interferences, which complicate the quantification of these metals with high accuracy. To overcome errors arising from matrix effects—in particular, the highly varying major ion composition of the investigated ground water samples—an isotope dilution analysis and quantification based on standard additions, respectively, were performed. The method allowed to process four samples per hour in a fully automated mode. With a sample volume of only 8 mL, enrichment factors of 6–9 could be achieved, yielding detection limits <1 ng L−1. Validation of the trueness was performed based on the reference samples. This method has been used for the analysis of the total concentrations of Ag, Pt, Pd and Au in highly mineralized ground waters collected from springs located in important geological fault zones of Austria’s territory. Concentrations ranges of 0.21–64.2 ng L−1 for Ag, 0.65–6.26 ng L−1 for Pd, 0.07–1.55 ng L−1 for Pt and 0.26–1.95 ng L−1 for Au were found.

Highlights

Natural mineral waters and medicinal waters are certain types of ground waters that are distinguished from drinking water by their high purity at the source and specific chemical and physical characteristics
We report the development and optimization of a methodological approach for the determination of selected precious metals (Ag, Pd, Pt and Au) in highly mineralized ground waters, referred to as mineral waters according to the regulations, Molecules 2021, 26, 7253 as Cd interferences on 106Pd and 108Pd or Hg interferences on 196Pt and 198Pt, which are not resolvable even by a mass resolution of m/∆m < 10,000, complicate the analysis
We report the development and optimization of a methodological approach for the determination of selected precious metals (Ag, Pd, Pt and Au) in high3lyof 21 mineralized ground waters, referred to as mineral waters according to the regulations, based on solid-phase extraction (SPE) on the strong anion exchange resin TEVA® Resin and online coupled batoseIdCPo-nSFSMPES uosnintghemsetmrobnrganaendioensoelvxacthioanngaes raessainmTpEleViAnt®roRdeuscitnionansdysotenmlin

Summary

Introduction

Natural mineral waters and medicinal waters are certain types of ground waters that are distinguished from drinking water by their high purity at the source and specific chemical and physical characteristics. Inefficient separation of Sr and Mo from the target analytes on the anion exchange resin resulted in a contribution of the respective oxide species, which were much higher compared to the low concentrations expected for the target analytes We studied this effect by analyzing a standard curve containing 1–100-μg L−1 Mo in 0.024-M L−1 HCl (total Mo concentrations from 0.01 to 78.72 μg L−1 were measured in the investigated ground water samples; published in Reference [27] (the version in German language only)) with the matrix separation/pre-concentration method directly coupled to ICP-SFMS using a Scott-type Teflon® PFA spray chamber. This approach was necessary, as uncorrected intensities, resulting in incorrect isotope ratios, would have increased the concentrations—depending on the Cd concentration—up to 27% and, in some samples, even by a factor of 2.5–8.3

Matrix Effects

Validation

Background Concentrations in Ground Water

Chemicals and Laboratory Materials

Samples and Reference Samples for Quality Control

ICP-SFMS

Standardization

Findings

Conclusions