Multielement Detection of Nonmetals by Barium-Based Post-ICP Chemical Ionization Coupled to Orbitrap-MS.

Prevalence of F, Cl, S, P, Br, and I in pharmaceuticals and environmental contaminants has promoted standard-free quantitation using analyte-independent heteroatom responses in inductively coupled plasma (ICP)-MS. However, in-plasma ionization challenges and element-dependent isobaric interference removal methods have hampered the multielement nonmetal detection in ICP-MS. Here, we examine an alternative approach to enhance multielement detection capabilities. Analytes are introduced into an ICP leading to post-plasma formation of HF, HCl, H3PO3, H2SO4, HBr, and HI, which are then chemically ionized to BaF+, BaCl+, BaH2PO3+, BaHSO4+, BaBr+, and BaI+ via reactions with barium-containing ions supplied by a nanospray. Subsequent ion detection by high-resolution MS provides an element-independent approach for resolving isobaric interferences. We show that elemental response factors using these ions are linear within 2 orders of magnitude and independent of analytes' chemical structures. Using a single set of operating parameters, detection limits <1 ng/mL are obtained for Cl, Br, I, and P, while those for F and S are 1.8 and 6.2 ng/mL, respectively, offering improved multielement quantitation of nonmetals. Further, insights into ionization mechanisms indicate that the reactivities of reagent ions follow the order BaNO2+ > BaHCO2+ > Ba(H2O)n2+ ∼ BaCH3CO2+. Notably, the least reactive ions are generated directly by nanospray, suggesting that modification of these ions via interaction with plasma afterglow is critical for achieving good sensitivities. Moreover, our experiments indicate that the element-specific plasma products follow the order HF < H2SO4 ∼ HCl < H3PO3 ∼ HBr ∼ HI for their propensity to react with reagent ions. These insights provide guidelines to manage matrix effects and offer pathways to further improve the technique.

Solution Cathode Glow Discharge Coupled to Atmospheric Pressure Chemical Ionization for Elemental Detection of S and P in Organic Compounds.

We report a post-plasma chemical ionization approach to evaluate solution cathode glow discharge (SCGD) for S and P elemental analysis. Here, the SCGD serves as a reactor to produce chemical vapors for S and P from organic compounds containing these elements, while a corona discharge operated in negative mode is used to ionize the products. The approach creates long-lived ions in atmospheric pressure, enabling direct investigation of chemical vapor products via mass spectrometric and ion mobility separations. The investigations indicate that SCGD converts S and P to H2SO4 and H3PO4, respectively. These species are then ionized as HSO4HNO3 - and H3PO4NO3HNO3- via reactions with NO3HNO3- produced by corona discharge. The response factors for P among several small molecules varies within 10% of the average response from the compounds, suggesting a reasonable species-independent characteristic. The response factors for S show larger variations among compounds, indicating a higher dependence of chemical vapor generation efficiency on analytes' chemical structures. Detection limits of 15 and 29 ng/mL are achieved for P and S detection, respectively. These figures are limited by background equivalent concentrations and low ion flux in the utilized ion mobility-time of flight mass spectrometer, indicating potential for significant improvements. In particular, the specificity of clustering for S and P-containing ions produced in this approach suggest facile analysis of S and P using quadrupole-based mass spectrometers for improved analytical performance.

High-Resolution Elemental Mass Spectrometry Using LC-ICP-Nanospray-Orbitrap for Simultaneous and Species-Independent Quantitation of Fluorinated and Chlorinated Compounds.

Simultaneous elemental detection of F and Cl offers quantitation of fluorinated and chlorinated compounds and their transformation products without compound-specific standards. Despite wide-ranging applications, this capability has been hindered by fundamental and technical shortcomings of current inductively coupled plasma (ICP)-MS methods in ion formation and isobaric interference elimination. These hurdles are alleviated here via a chemical ionization method. Fluorine and chlorine in analytes are first converted to HF and HCl by an ICP with post-plasma recombination and subsequently react with barium-containing ions supplied by a nanospray, yielding BaF+ and BaCl+ as elemental reporter ions. Notably, the method is readily interfaced to an Orbitrap MS which eliminates isobaric interferences at resolving powers as low as 35,000, far greater than that of current ICP-MS instruments. Moreover, the instrument is easily reverted to the ESI-MS mode for complementary molecular characterization. To demonstrate analytical capabilities, a workflow for rapid quantitation of compounds separated by reversed-phase liquid chromatography is developed using a species-independent calibration. The independent F and Cl measurements agree with each other, providing recoveries of >90% and LODs of 8-12 pmol Cl and 5-12 pmol F on the column. The workflow along with LC-ESI-MS on the same instrument is then applied to identify and quantify in-vitro drug metabolites, yielding total drug-related material recoveries of >80% and quantitation of minor metabolites summing to 8% of the total drug-related compounds. These results highlight the strengths of simultaneous F and Cl speciation for rapid quantitation with applications in early drug development.

F-doping of nanostructured ZnO: a way to modify structural, electronic, and surface properties.

Polycrystalline ZnO is a material often used in heterogeneous catalysis. Its properties can be altered by the addition of dopants. We used gaseous fluorine (F2(g)) as direct way to incorporate fluoride in ZnO as anionic dopants. Here, the consequences of this treatment on the structural and electronic properties, as well as on the acidic/basic sites of the surface, are investigated. It is shown that the amount of F incorporation into the structure can be controlled by the synthesis parameters (t, T, p). While the surface of ZnO was altered as shown by, e.g., IR spectroscopy, XPS, and STEM/EDX measurements, the F2 treatment also influenced the electronic properties (optical band gap, conductivity) of ZnO. Furthermore, the Lewis acidity/basicity of the surface was affected which is evidenced by using, e.g., different probe molecules (CO2, NH3). In situ investigations of the fluorination process offer valuable insights on the fluorination process itself.

Polyhalogen and Polyinterhalogen Anions from Fluorine to Iodine.

This Review deals with the evolving field of polyhalogen chemistry, specifically polyhalogen anions (polyhalides). In addition to a historical outline, current progress in synthetic approaches towards the formation of polyfluorides, polychlorides, polybromides, and polyinterhalides is also illustrated. The structural diversity of polyhalides has substantially increased in the past decade, especially for polychlorides and polybromides, which are commonly characterized by single-crystal X-ray diffraction, Raman spectroscopy, and quantum-chemical calculations. Polyfluorides have been examined by sophisticated state-of-the-art quantum-chemical calculations and investigated spectroscopically in noble gas matrix-isolation experiments under cryogenic conditions at 4 K. The bonding in such polyhalide systems is also discussed. The last Section deals with applications of polyhalides in halogenation reactions and electrochemistry as well as their use as reactive ionic liquids, emphasizing the promising future of polyhalogen chemistry.

IR-Laser Ablation of Potassium Cyanide: A Surprisingly Simple Route to Polynitrogen and Polycarbon Species.

Pulsed laser irradiation of solid potassium cyanide (KCN) produces, besides free nitrogen and carbon atoms, the molecular species KN and KC which are potential candidates for interstellar species of potassium. Additionally, N3 , N3 - , KN3 , C3 , C3 - , and KC3 are produced and isolated in solid noble gases as well as in solid N2 . Molecular potassium nitrene (KN) reacts with dinitrogen in neon and argon matrices after photochemical excitation (λ=470 nm) forming molecular end-on (C∞v ) and side-on (C2v ) potassium azide isomers. The side-on isomer (C2v ) is thermodynamically favored at the CCSD(T)/ma-def2-TZVP level of theory. It can be obtained from the end-on isomer by UV-irradiation (λ=273 nm).

Investigation of Molecular Alkali Tetrafluorido Aurates by Matrix-Isolation Spectroscopy.

Molecular alkali tetrafluorido aurate ion pairs M[AuF4 ] (M=K, Rb, Cs) are produced by co-deposition of IR laser-ablated AuF3 and MF in solid neon under cryogenic conditions. This method also yields molecular AuF3 and its dimer Au2 F6 . The products are characterized by their Au-F stretching bands and high-level quantum-chemical calculations at the CCSD(T)/triple-ζ level of theory. Structural changes in AuF4 - associated with the coordination of the anion to different alkali cations are proven spectroscopically and discussed.

The Crystal Structure of α-F2 : Solving a 50 Year Old Puzzle Computationally.

The cohesive energy of α-fluorine, with C2/c space group symmetry, was calculated at benchmark quality by applying the method of increments. The known experimental X-ray structure data needed to be refined, since the reported intramolecular bond length was unrealistically large. At the CCSD(T) level, including corrections for zero-point energy, the basis set superposition error, and extrapolated to the complete basis set limit, a cohesive energy of -8.72 kJ mol-1 was calculated, which agrees well with the 0 K-extrapolated experimental value of -8.35 kJ mol-1 . Comparison of the C2/c structure with a Cmca structure, isotypic to that of chlorine, bromine, and iodine reveals that the origin of the different structure of solid fluorine, compared to the heavier halogens, is the lack of significantly stabilizing σ-hole interactions. In addition, the wave numbers of the stretching mode in solid fluorine were calculated at coupled cluster level and compared to newly recorded Raman spectra of condensed fluorine. Both experiment and calculation indicate a slight up-shift for the stretching mode by 2 or 5 cm-1 , respectively, with respect to a free F2 molecule in the gas phase.