Distinction and quantitation of leucine-isoleucine isomers and lysine-glutamine isobars by electrospray ionization tandem mass spectrometry (MS(n), n = 2, 3) of copper(II)-diimine complexes

Electrospray ionization of mixtures of isomeric and isobaric amino acids was investigated with the goal of distinguishing and quantifying the components. Isomeric amino acids leucine and isoleucine were readily distinguished and quantified in 90 : 10 to 10 : 90 binary mixtures using two-stage (MS(2)) and three-stage (MS(3)) tandem mass spectrometric dissociations of ternary Cu(2+)-2, 2'-bipyridyl (bpy) complexes, [Cu(AA - H)bpy](+). The complexes self-assembled in solution upon mixing the components and provided a convenient means of efficient derivatization that increased the efficiency of amino acid ionization by electrospray and shifted the mass of the analytes to a region which was free of solvent interferences. Low-energy dissociations of [Cu(AA - H)bpy](+) complexes in a quadrupole ion trap were achieved at >90% conversions and >80% trapping efficiencies for the MS(2) and MS(3) precursor and fragment ions. Isobaric amino acids glutamine and lysine were also distinguished through MS(2) and MS(3) of their ternary complexes with Cu(2+) and bpy. ESI of [Cu(Gln - H)bpy](+) was enhanced in the presence of [Cu(Lys - H)bpy](+), which resulted in non-linear response at low Lys concentrations.     

Synthesis of zirconocene-based silica phases and evaluation in lindane and heptachlor epoxide adsorption/desorption

Silica (350 m(2) g(-1)) was chemically modified with Cp2ZrCl2 and (nBuCp)2ZrCl2 by grafting. Hybrid silica bearing surface indene groups was synthesized by the sol-gel method, followed by metallation with ZrCl(4)2THF. The resulting phases were characterized by Rutherford backscattering spectrometry (RBS), 13C and 29Si magic angle spin nuclear magnetic resonance, X-ray photoelectron spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy. According to RBS measurements, metal content was 0.2- to 0.3-wt% Zr/SiO2 for the grafted systems and 4.5-wt% Zr/SiO2 for the phase prepared by the sol-gel method. The solid phases were evaluated for the adsorption/preconcentration of lindane and heptachlor epoxide from aqueous solution. For comparative reasons, the commercial LC-18 phase was also evaluated. Analyte concentration was monitored by gas chromatography electron capture detection. For the grafted phases, the coordination sphere around the metal center seems not to influence the adsorption/desorption properties of these phases vis-a-vis the studied analytes. In the case of the phases prepared by the sol-gel method, recovery results were comparable to those observed for LC-18. Experiments using ZrO2 and ZrO2/SiO2 phases led to lower recovery results.     

Copper-mediated intra-ligand oxygen transfer in gas-phase complexes with 3-nitrotyrosine

Gas-phase ternary complexes with Cu(II) and 2,2'-bipyridine (bpy) of tyrosine, 3-aminotyrosine, 3-nitrotyrosine and 3-nitrotyrosine methyl ether are formed readily upon electrospraying aqueous methanol solutions containing the components. In contrast to Cu(bpy) complexes of tyrosine, 3-aminotyrosine and other aromatic amino acids, the complexes of 3-nitrotyrosine and its methyl ether undergo unusual collisionally activated dissociations (CADs) that involve Cu-mediated transfer of an oxygen atom from the nitro group. With 3-nitrotyrosine this results in an expulsion of carbonic acid, H(2)CO(3), whereas with 3-nitrotyrosine methyl ether an OH migration forms Cu(OH)bpy(+) as the predominant product. To the best of our knowledge, this is the first case of an intra-ligand redox reaction in a gas-phase organometallic complex. The reaction mechanism of this unusual dissociation was elucidated by a combination of isotope labeling, accurate mass measurements, energy-resolved CAD mass spectra and density functional theory calculations of ion structures and relative energies.     

A neutron monitor for in-situ real-time determination of transuranics in a processed waste effluent stream

A pilot plant operation at the Savannah River Site will remove ⁹⁰Sr, ¹³⁷Cs, and transuranics from a high-level liquid waste stream prior to encapsulation in a Saltstone Facility. Monitors are required to determine the concentrations of all radionuclides, including transuranics, in real-time on this processed waste stream. A neutron counter used to measure the concentration of each actinide isotope present in the stream is described. The neutron counter assembly consists of nested annular layers of shielding, reflectors, detectors, and moderators. On-line, live-time system control and calibration is provided by a time-tagged neutron source embedded in the moderator assembly.