Photochemical vapor generation (PVG) was coupled to direct analysis in real time (DART) high-resolution mass spectrometry (HRMS) using N2 as the discharge gas in an attempt to identify unknown volatile carbonyls of Ru and Os generated during the UV photolysis of HCOOH-based photochemical media previously described in the literature. Initial insights into the ambient ionization process in the N2 DART were gained using volatile W(CO)6 and Fe(CO)5, either photochemically generated or introduced as standards from a headspace. In general, significant changes in the original carbonyl structure are observed in both positive and negative ion modes, characterized by the loss of CO group(s), oxidation, hydration, and formation of various adducts derived from N2 used as the discharge gas. Nevertheless, the ions detected under PVG conditions based on dilute or concentrated HCOOH media, preferably in the presence of transition metal mediators, suggest that the generated carbonyls of Ru and Os are mononuclear, contain five carbonyl groups, and are therefore Ru(CO)5 and Os(CO)5. When Co2+ was used as a mediator, some difficulties in identification were encountered because volatile Co(CO)4H was cogenerated with significant efficiency, overloading the DART and HRMS and even resulting in mixed metal carbonyl cluster ions during ionization. Additional experiments with PVG of Os conducted under oxidative conditions using deionized water, dilute HNO3, and dilute H2O2 as the photochemical media confirmed OsO4 as the volatile species. The same volatile species was also identified as the dominant product using dilute CH3COOH with the addition of Fe2+ as a mediator, suggesting the rather oxidative nature of this medium, although some distinct carbonyl/hydrido/methyl or acetato species were also observed. The controversies are discussed as well as other peculiarities of the DART-HRMS technique for the identification of volatile metal carbonyls.

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A sensitive method for Rh determination was developed by coupling photochemical vapor generation (PVG) for sample introduction to inductively coupled plasma mass spectrometry (ICPMS). PVG was conducted in a thin-film flow-through photoreactor operated in a flow injection mode from a photochemical medium comprising 10 M HCOOH. PVG efficiency was substantially enhanced by the addition of 10 mg L-1 Cu2+ and 5 mg L-1 Co2+ as mediators as well as 50 mM NaNO3. The volatile product (likely Rh(CO)4H) was found to be less stable when in prolonged contact with the liquid medium at the output from the photoreactor. Hence, further enhancement was achieved by introducing an Ar carrier gas near the exit of the photoreactor to minimize the interaction of volatile species with the liquid medium. Despite PVG efficiency reaching only 15%, measurement at the ultratrace level (20 ng L-1) was characterized by very good repeatability of peak area response (2.9%) and outstanding limits of detection (13 pg L-1, 6.5 fg absolute) using He in the collision cell. Interferences from potential coexisting metals, inorganic acids, and their anions were investigated. Accuracy was verified by analysis of OREAS 684 (Platinum Group Element Ore) and SRM 2556 (Used Auto Catalyst) following peroxide fusion for sample preparation. Application to the direct analysis of real river and lake water samples and reference materials AQUA-1 and SLRS-6 demonstrated excellent selectivity of the PVG-ICPMS methodology over conventional pneumatic nebulization-ICP(MS)/MS, the results of which were seriously biased by polyatomic interferences, especially from Sr and Cu, despite the use of various reaction/collision cell modes.

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Herein, we report on surprisingly efficient photochemical vapor generation (PVG) of Ru, Re, and especially Ir, achieved from very dilute HCOOH media employing a thin-film flow-through photoreactor operated in flow injection mode. In the absence of added metal ion sensitizers, efficiencies near 20% for Ir and approximately 0.06% for Ru and Re occur in a narrow range of HCOOH concentrations (around 0.01 M), significantly higher than previously reported from conventionally optimized HCOOH concentrations (1-20 M). A substantial enhancement in efficiency, to around 9 and 1.5%, could be realized for Ru and Re, respectively, when 0.005 M HCOONa served as the PVG medium. The addition of metal ion sensitizers (particularly Cd2+ and Co2+) to 0.01 M HCOOH significantly enhanced PVG efficiencies to 17, 2.2, and 81% for Ru, Re, and Ir, respectively. Possible mechanistic aspects occurring in dilute HCOOH media are discussed, wherein this phenomenon is attributed to the action of 185 nm radiation available in the thin-film flow-through photoreactor. An extended study of PVG of Fe, Co, Ni, As, Se, Mo, Rh, Te, W, and Bi from both dilute HCOOH and CH3COOH was undertaken, and several elements for which a similar phenomenon appears were identified (i.e., Co, As, Se, Te, and Bi). Although use of dilute HCOOH media is attractive for practical analytical applications employing PVG, it is less tolerant toward dissolved gases and interferents in the liquid phase due to the likely lower concentrations of free radicals and aquated electrons required for analyte ion reduction and product synthesis.

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Herein, we describe the highly efficient photochemical vapor generation (PVG) of a volatile species of Ir (presumably iridium tetracarbonyl hydride) for subsequent detection by inductively coupled plasma mass spectrometry (ICPMS). A thin-film flow-through photoreactor, operated in flow injection mode, provided high efficiency following optimization of identified key PVG parameters, notably, irradiation time, pH of the reaction medium, and the presence of metal sensitizers. For routine use and analytical application, PVG conditions comprising 4 M formic acid as the reaction medium, the presence of 10 mg L-1 Co2+ and 25 mg L-1 Cd2+ as added sensitizers, and an irradiation time of 29 s were chosen. An almost 90% overall PVG efficiency for both Ir3+ and Ir4+ oxidation states was accompanied by excellent repeatability of 1.0% (n = 15) of the peak area response from a 50 ng L-1 Ir standard. Limits of detection ranged from 3 to 6 pg L-1 (1.5-3 fg absolute), dependent on use of the ICPMS reaction/collision cell. Interferences from several transition metals and metalloids as well as inorganic acids and their anions were investigated, and outstanding tolerance toward chloride was found. Accuracy of the developed methodology was verified by analysis of NIST SRM 2556 (Used Auto Catalyst) following peroxide fusion for sample preparation. Practical application was further demonstrated by the direct analysis of spring water, river water, lake water, and two seawater samples with around 100% spike recovery and no sample preparation except the addition of formic acid and the sensitizers.

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