Measurement of PCDDs, PCDFs, and non-ortho-PCBs by comprehensive two-dimensional gas chromatography-isotope dilution time-of-flight mass spectrometry (GC x GC-IDTOFMS)

Comprehensive two-dimensional gas chromatography with isotope-dilution time-of-flight mass spectrometry (GC × GC-IDTOFMS) was used to measure polychlorinated dibenzo-p-dioxin (PCDD), polychlorinated dibenzofuran (PCDF), and coplanar polychlorinated biphenyl (cPCB) concentrations in ash, sediment, vegetation, and fish samples. The GC × GC capability was achieved by using a quad jet, dual stage, thermal modulator. Zone compression of the GC peaks from modulation resulted in a significant increase of the signal intensity over classical GC-IDTOFMS. The GC × GC column set used an Rtx-Dioxin 2 phase as the first dimension (¹D) and an Rtx-500 as the second dimension (²D). The chromatographic separation of the 17 PCDD/Fs and the 4 cPCBs was attained in ¹D except for 2,3,7,8-TCDD and CB126 for which deconvoluted ion currents (DIC) were required to be reported separately. The Rtx-500 phase separated the bulk matrix interfering compounds from the target analytes in ²D. The instrumental limit of detection (iLODs) was 0.5 pg for 2,3,7,8-TCDD. The calibration curves showed good correlation coefficients for all the compounds investigated in the concentration range of 0.5–200 pg. GC × GC-IDTOFMS results compared favorably to those from conventional isotope-dilution one-dimensional gas chromatography-high resolution mass spectrometry (GC-IDHRMS). The comprehensive mass analysis of the TOFMS further permitted the identification of other contaminants of concern in the samples.     

Ar等离子体对氟橡胶F2311表面的改性

利用氩气等离子对氟橡胶F2311进行表面亲水改性处理，通过接触角测量、X射线光电子能谱(XPS)对改性后的F2311进行分析，结果表明氩气等离子体处理可通过等离子体聚合在F2311表面形成含碳、氧、氮的覆盖层，可较好地改善F2311的表面亲水性，并有较好的表面动力学性质，获得的表面亲水性可以保持很长时间。     

Determination of tin in soil by continuous hydride generation and inductively coupled plasma mass spectrometry

A method was investigated for the determination of Sn in soil samples by KOH fusion followed by continuous hydride generation coupled with inductively coupled plasma mass spectrometry (HG-ICP-MS). Sample solutions in 3.0 M HCl were mixed in line with a solution of 2.4% NaBH₄ and 0.25 M KOH to generate stannane gas. The mixture was delivered continuously to a gas/liquid separator and the stannane gas was introduced into a Perkin-Elmer Sciex Elan 6000 ICP-MS for concentration measurements. A method detection limit of 0.45 mg/kg was sufficient for Sn levels commonly found in soil samples. Sn concentrations as low as 2.5 mg/kg were reproducibly measured in soil samples. Sample results by HG-ICP-MS agreed within ±17% relative difference to results by instrumental neutron activation analysis (INAA) and within ±6% relative difference to results by KOH fusion followed by inductively coupled plasma optical emission spectroscopy (ICP-OES).     

LC and LC-MS Separation of Peptides on Macrocyclic Glycopeptide Stationary Phases: Diastereomeric Series and Large Peptides

Previous work on the LC separation of peptides had shown that macrocyclic glycopeptide stationary phases to be selective for peptides of five to thirteen amino acids in length. In this work, the selectivity of the teicoplanin stationary phase is compared to that of a C18 stationary phase for seven diastereomeric enkephalin peptides. The teicoplanin stationary phase separated all seven diastereomeric enkephalin peptides in a single chromatographic run. The insertion of d-amino acids into the primary enkephalin sequence produced areas of hydrophobicity that influenced retention order on the C18 stationary phase. However, analogous trends are not observed on the teicoplanin stationary phase, which is more polar and structurally diverse. Optimization of the mobile phase and the use of a step-gradient for the enkephalin separation on the teicoplanin stationary phase is discussed. Also, the selectivity of macrocyclic glycopeptide stationary phases for peptides of 14, 28, 30, and 36 amino acids also is investigated and compared to separation on a C18 stationary phase. A method for eluting peptides with multiple basic amino acids, which tend to be strongly retained on the macrocyclic glycopeptide stationary phases, is presented.     

Determination of aluminum in highly concentrated iron samples: Study of interferences using high-resolution continuum source atomic absorption spectrometry

High-resolution continuum source atomic absorption spectrometry (HR-CS AAS) has been used to investigate spectral and non-spectral interferences found with a conventional line source atomic absorption spectrometer in the determination of aluminum in pharmaceutical products containing elevated iron and sugar concentrations. A transversely heated graphite furnace was used as the atomizer in both spectrometers. The two most sensitive aluminum lines at 309.3 nm and 396.2 nm were investigated and it was found that an iron absorption line at 309.278 nm, in the vicinity of the aluminum line at 309.271 nm, could be responsible for some spectral interference. The simultaneous presence of iron and the organic components of the matrix were responsible for radiation scattering, causing high continuous and also structured background absorption at both wavelengths. The aluminum and iron absorption could not be separated in time, i.e., the iron interference could not be eliminated by optimizing the graphite furnace temperature program. However, an interference-free determination of aluminum was possible carrying out the measurements with HR-CS AAS at 396.152 nm after applying least squares background correction for the elimination of the structured background. Analytical working range and other figures of merit were determined and are presented for both wavelengths using peak volume registration (center pixel ± 1) and the center pixel only. Limits of detection and characteristic masses ranged from 1.1 to 2.5 pg and 13 to 43 pg, respectively. The method was used for the determination of the aluminum contamination in pharmaceutical formulations for iron deficiency treatment, which present iron concentrations from 10 to 50 g l^− 1. Spike recoveries from 89% to 105% show that the proposed method can be satisfactorily used for the quality control of these formulations.     

Closed‐form rectangular atomic wave functions of an N‐dimensional atom

A closed‐form expression has been derived to obtain the N‐dimensional rectangular atomic wave functions. The wave functions can be obtained straightforwardly with the knowledge of the angular momentum quantum numbers and the dimension and there is no need to employ recursive methods as in previous works. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 263–274, 2002     

失效原子力显微镜硅针尖再生

原子力显微镜的传统商品硅针尖在使用过程中极易因磨损而失效，本文研究了一种在实验室条件下简易可行的回收利用失效硅针尖的方法。在原子力显微镜的敲击模式下使用曲率半径大于100 nm的失效硅针尖对生长单壁碳纳米管的样品表面进行扫描，把样品表面的单壁碳纳米管管束粘接到硅针尖上，可制得直径在5～20 nm的碳纳米管针尖。实验对碳纳米管针尖和新的商品硅针尖进行了成像对比，所制备的碳纳米管针尖不仅在成像分辨率而且在成像稳定性上都优于新的商品硅针尖。     

改性凹凸棒的制备及对砷离子的吸附研究

针对日益严重的砷离子污染问题，本文采用灵敏简便的原子荧光分析法，探究了凹凸棒石粘土吸附剂对砷离子的吸附性能，测定了pH、吸附时间、砷离子的初始浓度等因素对凹凸棒石粘土负载铁氧化物对砷离子吸附能力的影响，并通过SEM、EDX、FTIR对所制得的吸附剂进行了表征研究，同时进行了吸附动力学和吸附等温模型的分析。研究结果表明，改性后的凹凸棒对砷离子的吸附性能有了显著提升，在较低浓度时吸附效率可达98%，该吸附符合Langmuir等温吸附模型和准二级动力学方程。     

Surprising Homolytic Gas Phase Co−C Bond Dissociation Energies of Organometallic Aryl-Cobinamides Reveal Notable Non-Bonded Intramolecular Interactions

Aryl-cobalamins are a new class of organometallic structural mimics of vitamin B₁₂ designed as potential ‘antivitamins B₁₂’. Here, the first cationic aryl-cobinamides are described, which were synthesized using the newly developed diaryl-iodonium method. The aryl-cobinamides were obtained as pairs of organometallic coordination isomers, the stereo-structure of which was unambiguously assigned based on homo- and heteronuclear NMR spectra. The availability of isomers with axial attachment of the aryl group, either at the ‘beta’ or at the ‘alpha’ face of the cobalt-center allowed for an unprecedented comparison of the organometallic reactivity of such pairs. The homolytic gas-phase bond dissociation energies (BDEs) of the coordination-isomeric phenyl- and 4-ethylphenyl-cobinamides were determined by ESI-MS threshold CID experiments, furnishing (Co−C )-BDEs of 38.4 and 40.6 kcal mol⁻¹, respectively, for the two β-isomers, and the larger BDEs of 46.6 and 43.8 kcal mol⁻¹ for the corresponding α-isomers. Surprisingly, the observed (Co−C )-BDEs of the Co_β-aryl-cobinamides were smaller than the (Co−C )-BDE of Co_β-methyl-cobinamide. DFT studies and the magnitudes of the experimental (Co−C )-BDEs revealed relevant contributions of non-bonded interactions in aryl-cobinamides, notably steric strain between the aryl and the cobalt-corrin moieties and non-bonded interactions with and among the peripheral sidechains.