Ultrasensitive Detection of Ruthenium by Coupling Cobalt and Cadmium Ion-Assisted Photochemical Vapor Generation to Inductively Coupled Plasma Mass Spectrometry

Abstract

An extremely sensitive methodology for the determination of Ru was developed by coupling photochemical vapor generation (PVG) analyte introduction with inductively coupled plasma mass spectrometry (ICPMS). PVG was undertaken with a thin-film flow-through photoreactor in a medium comprising 8 M formic acid in the presence of 10 mg L −1 Co 2+ and 25 mg L −1 Cd 2+ . The volatile product (presumably ruthenium pentacarbonyl) was generated in a flow injection mode, yielding an overall efficiency of 29% at a sample flow rate of 1.4 mL min −1 . The presence of both Co 2+ and Cd 2+ sensitizers enhanced PVG efficiency by 3,200-fold, permitting a 31 s irradiation time. Although enhanced efficiency (≈40%) could be obtained with increased Co 2+ concentration, this was not suitable for routine use due to co-generation of cobalt carbonyl. Excellent repeatability (<2.5%) and reproducibility (4%) were achieved for 200 ng L −1 Ru 3+ . Limits of detection ranged from 20 to 42 pg L −1 (10−21 fg absolute) depending on the measured isotope and operational mode of the ICPMS reaction/collision cell. Interferences from inorganic acids and their anions, several transition metals, and metalloids were investigated. Practical application of the methodology was demonstrated by the analysis of seven water samples of various matrix complexities (well water, spring water, contaminated water, and seawater).

GC-MS exploration of photochemically generated species of Os, W and Ru from reductive and oxidative media

“…Based on chemistry and prior similar syntheses of same group compounds, it was believed that the volatile products generated in these experiments would be Ru(CO) 5 (ref. 28) and W(CO) 6 (ref. 26) from a formic acid medium, OsO 4 (and RuO 4 ) from dilute nitric acid, 6,27 and a carbonylated compound of Os in a reductive solution of acetic acid.…”

“…Both laboratories used the same photochemical reactor, a low pressure 19 W flow-through Hg discharge lamp (Beijing Titan Instrument Co. Ltd., Beijing, China) fitted with an internal channel of synthetic quartz (0.72 mL internal irradiated volume) through which the sample was continuously pumped to expose the analyte solution to (primarily) 185 and 254 nm radiation. 26–28 The irradiated sample was conducted to gas–liquid phase separators (GLS system) fed with a flow of Ar purge gas which served to strip volatile species from the liquid phase and permitted convenient manual syringe sampling of 100–500 μL effluent volumes of gas for analyte characterization by GC-MS.…”

“…PVG was undertaken in accordance with the optimized procedures, apparatus and reagents recently reported for W, 26 Os 27 and Ru. 28 Several minor deviations from the published protocols included use of a lower (100 mL min −1 ) flow rate of Ar transfer gas through the GLS unit(s) to decrease dilution of the analyte in the sampled gas phase and, for studies of W, two gas–liquid phase separators (GLS, 15 mL volume) used in series in an effort to ensure elimination/minimization of water droplet carryover to the syringe sampler. The first GLS unit was as described earlier, 26 whereas the second GLS was fitted with a modified cap (a 15 mL polypropylene vial containing 3 ports in the screw cap) to conveniently introduce the gas phase from the first GLS, connected via PTFE tubing, while allowing for both simultaneous syringe sampling through a second port without obstructing gas flow through the third port to an exhaust unit.…”

“…Samples were continuously photolysed at a solution flow rate of 2 mL min −1 to provide for a steady-state supply of analyte species from elevated concentrations of W( vi ), Os( iv ) and Ru( iii ), in the 5–40 mg L −1 range in appropriate media, 26–28 to enhance their detection using GC-MS.…”

“…Herein, we provide GC-MS evidence identifying W(CO) 6 as the stable product of PVG of W( vi ) generated from a reductive solution of formic acid in the presence of 500 mg L −1 Cd( ii ) sensitizer, 26 as well as OsO 4 arising from the oxidative PVG of a solution of Os( iv ) in dilute nitric acid. 5,6,27 Analytical products of reductive PVG of Ru( iii ) 28 from formic acid in the presence of 10 mg L −1 Co( ii ) and 25 mg L −1 Cd( ii ) sensitizers, as well as Os( iv ) 27 from acetic acid containing 50 mg L −1 Co( ii ), remain unidentified.…”