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Paired ion electrospray ionization (PIESI) mass spectrometry was developed as a useful technique that provides sensitive detection for anions in the positive ion mode. The ion-pairing reagent (IPR) utilized plays an essential role affecting the detection limits. This work describes the design and synthesis of two novel dications with unsymmetrical structures and their utilization for anion detection and mechanistic insights. The performance of dications was evaluated for seven selected anions in both single ion monitoring (SIM) mode and selected reaction monitoring (SRM) mode. The unsymmetrical dications allowed sensitive detection for these anions with down to subpicogram limits of detection (LOD) and an improved sensitivity from 1.5 to 12 times compared to the corresponding symmetrical dications. The enhanced sensitivity could be attributed to the surface activity of the unsymmetrical dications, which results in a concurrent strong partitioning of the anion to the aerosol droplet surface. Surface activity measurements of the anion/IPR complex were conducted, and a correlation between the observed ESI responses and the surface activity of the complex was found. The mechanism was further explored and explained based on the concepts of the equilibrium partitioning model (EPM). [ABSTRACT FROM AUTHOR]

Photochemical catalytic CO2 reduction to formate and methanol has been demonstrated in an aqueous homogeneous system at pH 5.0 comprising ruthenium(II) trisphenanthroline as the chromophore, pyridine as the CO2 reduction catalyst, KCl, and ascorbic acid as a sacrificial reductant, using visible light irradiation at 470 ± 20 nm. Isotopic labeling with 13CO2 yields the six-electron-reduced product 13CH3OH. After 1 h photolysis, the two-electron-reduced product formate and the six-electron-reduced product methanol are produced with quantum yields of 0.025 and 1.1 × 10–4, respectively. This represents 76 and 0.15 turnovers per Ru for formate and methanol, respectively, and 152 and 0.9 turnovers per Ru on an electron basis for formate and methanol, respectively. The system is inactive after 6 h irradiation, which appears largely to be due to chromophore degradation. A partial optimization of the methanol yield showed that high pyridine to Ru ratios are needed (100:1) and that the optimum pH is near 5.0. The presence of potassium salts enhances the yield in formate and methanol by 8- and 2-fold, respectively, compared to electrolyte-free solutions; however, other alkali and alkali earth cations have little effect. The addition of small amounts of solid metal catalysts immobilized on carbon had either no effect (M = Pt or Pd) or deleterious effects (M = Ni or Au) on methanol production. Addition of colloidal Pt resulted in no methanol production at all. This is in notable contrast with the pyridine-based electrocatalysis of CO2 to methanol in which metallic or conductive surfaces such as Pt, Pd, or p-type GaP are necessary for methanol formation. [ABSTRACT FROM AUTHOR]