Zirconium Interferences on the Detection of Silver Nanoparticles by Single Particle ICP-MS: Implications on Natural Water Analysis

Abstract

The analysis of silver nanoparticle (NP Ag) by the single particle technique with argon plasma-coupled mass spectrometry (SP-ICP-MS) is an increasingly used analytical approach. The sensitive technique, distinguishing particle size distribution, allows working at concentrations similar to those found in environmental samples. The two natural Ag isotopes 107 and 109, with abundances of 52 and 48% respectively, have similar sensitivity in ICP-MS detection. However, it is common to encounter isobaric interferences in mass spectrometry, and the element silver is not an exception, as much with the 107 isotope as 109. For both isotopes, zirconium oxides present isobaric interferences, either 91Zr16O, 90Zr16O1H for the isotope 107 and the 92Zr16O1H for the 109. For surface water analysis by ICP-MS in regular technique, these interferences do not generally affect the analysis of total Ag concentrations as they can be then simply subtracted. On the other hand, detection of NP Ag was impacted by the interfering colloidal Zr. The analysis of Zr by the SP-ICP-MS technique of surface waters showed the presence of colloidal Zr, a random signal that cannot be simply subtracted from NP Ag signal. Our results showed that Zr colloids are effectively interfering with the NP Ag assays by SP-ICP-MS technique where interferences translated into a false positive. We proposed a calculation to evaluate a confidence threshold defining the maximum size that the false positives induced by Zr particles have on the silver particle detection. The analytical issue related to isobaric interferences from the naturally occurring colloidal Zr was attenuated by the use of the 109 isotope in the Ag particle detection, limiting false positive detections and improving the reliability of NP Ag measurements in natural waters. Therefore, more specific detection of NP Ag in surface waters that naturally contain Zr colloids can be accomplished.