Surfactant addition and alternating current electrophoretic oscillation during size fractionation of nanoparticles in channels with two or three different height segments

An array of parallel planar nanochannels containing two or three segments with varying inner heights was fabricated and used for size fractionation of inorganic and biological nanoparticles. A liquid suspension of the particles was simply drawn through the nanochannels via capillary action. Using fluorescently labeled 30 nm polyacrylonitrile beads, different trapping behaviors were compared using nanochannels with 200-45 nm and 208-54-30 nm height segments. Addition of sodium dodecyl sulfate (SDS) surfactant to the liquid suspension and application of an AC electric field were shown to aid in the prevention of channel clogging. After initial particle trapping at the segment interfaces, significant particle redistribution occurred when applying a sinusoidal 8V peak-to-peak oscillating voltage with a frequency of 150 Hz and DC offset of 4V. Using the 208-54-30 nm channels, 30 nm hepatitis B virus (HBV) capsids were divided into three fractions. When the AC electric field was applied to this trapped sample, all of the virus particles passed through the interfaces and accumulated at the channel ends.     

Differentiation and characterization of isotopically modified silver nanoparticles in aqueous media using asymmetric-flow field flow fractionation coupled to optical detection and mass spectrometry

The principal objective of this work was to develop and demonstrate a new methodology for silver nanoparticle (AgNP) detection and characterization based on asymmetric-flow field flow fractionation (A4F) coupled on-line to multiple detectors and using stable isotopes of Ag. This analytical approach opens the door to address many relevant scientific challenges concerning the transport and fate of nanomaterials in natural systems. We show that A4F must be optimized in order to effectively fractionate AgNPs and larger colloidal Ag particles. With the optimized method one can accurately determine the size, stability and optical properties of AgNPs and their agglomerates under variable conditions. In this investigation, we couple A4F to optical absorbance (UV–vis spectrometer) and scattering detectors (static and dynamic) and to an inductively coupled plasma mass spectrometer. With this combination of detection modes it is possible to determine the mass isotopic signature of AgNPs as a function of their size and optical properties, providing specificity necessary for tracing and differentiating labeled AgNPs from their naturally occurring or anthropogenic analogs. The methodology was then applied to standard estuarine sediment by doping the suspension with a known quantity of isotopically enriched ¹⁰⁹AgNPs stabilized by natural organic matter (standard humic and fulvic acids). The mass signature of the isotopically enriched AgNPs was recorded as a function of the measured particle size. We observed that AgNPs interact with different particulate components of the sediment, and also self-associate to form agglomerates in this model estuarine system. This work should have substantial ramifications for research concerning the environmental and biological fate of AgNPs.     

Simultaneous speciation of mercury and butyltin compounds in natural waters and snow by propylation and species-specific isotope dilution mass spectrometry analysis

A robust method has been developed for simultaneous determination of mercury and butyltin compounds in aqueous samples. This method is capable of providing accurate results for analyte concentrations in the picogram per liter to nanogram per liter range. The simultaneous determination of the mercury and tin compounds is achieved by species-specific isotope dilution, derivatization, and gas chromatography–inductively coupled plasma mass spectrometer (GC–ICP–MS). In derivatization by ethylation and propylation, reaction conditions such as pH and the effect of chloride were carefully studied. Ethylation was found to be more sensitive to matrix effects, especially for mercury compounds. Propylation was thus the preferred derivatization method for simultaneous determination of organomercury and organotin compounds in environmental samples. The analytical method is highly accurate and precise, with RSD values of 1 and 3% for analyte concentrations in the picogram per liter to nanogram per liter range. By use of cleaning procedures and SIDMS blank measurements, detection limits in the range 10–60 pg L^–1 were achieved; these are suitable for determination of background levels of these contaminants in environmental samples. This was demonstrated by using the method for analysis of real snow and seawater samples. This work illustrates the great advantage of species-specific isotope dilution for the validation of an analytical speciation method—the possibility of overcoming species transformations and non-quantitative recovery. Analysis time is saved by use of the simultaneous method, because of the use of a single sample-preparation procedure and one analysis.     

Efficient Access to Deuterated and Tritiated Nucleobase Pharmaceuticals and Oligonucleotides using Hydrogen‐Isotope Exchange

A general approach for the efficient hydrogen‐isotope exchange of nucleobase derivatives is described. Catalyzed by ruthenium nanoparticles, using mild reaction conditions, and involving either D₂ or T₂ as isotopic sources, this reaction possesses a wide substrate scope and a high solvent tolerability. This novel method facilitates the access to essential diagnostic tools in drug discovery and development: tritiated pharmaceuticals with high specific activities and deuterated oligonucleotides suitable for use as internal standards during LC‐MS quantification.     

Ions Can Move a Proton‐Coupled Electron‐Transfer Reaction into Tunneling Regime

The effects of charged species on proton‐coupled electron‐transfer (PCET) reaction should be of significance for understanding/application of important chemical and biological PCET systems. Such species can be found in proximity of activated complex in a PCET reaction, although they are not involved in the charge transfer process. Reported here is the first study of the above‐mentioned effects. Here, the effects of Na⁺, K⁺, Li⁺, Ca²⁺, Mg²⁺, and Me₄N⁺ observed in PCET reaction of ascorbate monoanions with hexacyanoferrate(III) ions in H₂O reveal that, in presence of ions, this over‐the‐barrier reaction entered into tunneling regime. The observations are: a) dependence of the rate constant on the cation concentration, where the rate constant is 71 (at I = 0.0023), and 821 (at 0.5M K⁺), 847 (at 1.0M Na⁺), and 438 M ^?1 s^?1 (at 0.011M Ca²⁺); b) changes of kinetic isotope effect (KIE) in the presence of ions, where k_H/k_D=4.6 (at I = 0.0023), and 3.4 (in the presence of 0.5M K⁺), 3.3 (at 1.0M Na⁺), 3.9 (at 0.001M Ca²⁺), and 3.9 (at 0.001M Mg²⁺), respectively; c) the isotope effects on Arrhenius pre‐factor where A_H/A_D=0.97 (0.15) in absence of ions, and 2.29 (0.60) (at 0.5M Na⁺), 1.77 (0.29) (at 1.0M Na⁺), 1.61 (0.25) (at 0.5M K⁺), 0.42 (0.16) (at 0.001M Ca²⁺) and 0.16 (0.19) (at 0.001M Mg²⁺); d) isotope differences in the enthalpies of activation in H₂O and in D₂O, where ΔΔH^?(D,H)=3.9 (0.4) kJ mol^?1 in the absence of cations, 1.3 (0.6) at 0.5M Na⁺, 1.8 (0.4) at 0.5M K⁺, 1.5 (0.4) at 1.0M Na⁺, 5.5 (0.9) (at 0.001M Ca²⁺), and 7.9 (2.8) (at 0.001M Mg²⁺) kJ mol^?1; e) nonlinear proton inventory in reaction. In the H₂O/dioxane 1 : 1, the observed KIE is 7.8 and 4.4 in the absence and in the presence of 0.1M K⁺, respectively, and A_H/A_D=0.14 (0.03). The changes when cations are present in the reaction are explained in terms of termolecular encounter complex consisting of redox partners, and the cation where the cation can be found in a near proximity of the reaction‐activated complex thus influencing the proton/electron double tunneling event in the PCET process. A molecule of H₂O is involved in the transition state. The resulting ‘configuration’ is more ‘rigid’ and more appropriate for efficient tunneling with Na⁺ or K⁺ (extensive tunneling observed), i.e., there is more precise organized H transfer coordinate than in the case of Ca²⁺ and Mg²⁺ (moderate tunneling observed) in the reaction.     

Direct determination of mercury in cosmetic samples by isotope dilution inductively coupled plasma mass spectrometry after dissolution with formic acid

A new method was proposed for the accurate determination of mercury in cosmetic samples based on isotopic dilution (ID)-photochemical vapor generation (PVG)-inductively coupled plasma mass spectrometry (ICP MS) measurement. Cosmetic samples were directly dissolved in formic acid solution and subsequently subjected to PVG for the reduction of mercury into vapor species following by ICP MS detection. Therefore, the risks of analyte contamination and loss were avoided. Highly enriched ²⁰¹Hg isotopic spike is added to cosmetics and the isotope ratios of ²⁰¹Hg/²⁰²Hg were measured for the quantitation of mercury. With ID calibration, the influences originating from sample matrixes for the determination of mercury in cosmetic samples have been efficiently eliminated. The effects of several experimental parameters, such as the concentration of the formic acid, and the flow rates of carrier gas and sample were investigated. The method provided good reproducibility and the detection limits were found to be 0.6 pg mL⁻¹. Finally, the developed method was successfully applied for the determination of mercury in six cosmetic samples and a spike test was performed to verify the accuracy of the method.     

Accurate measurement of uranium isotope ratios in soil samples using thermal ionization mass spectrometry equipped with a warp energy filter

A chemical and mass-spectrometric procedure for uranium isotopic analysis using a thermal ionisation mass spectrometer equipped with a Wide Aperture Retardation Potential energy filter has been developed and applied to uranium isotopic measurements for various soil samples. Soil samples were digested using a microwave digestor. Uranium was isolated from soil samples by the chemical separation procedure based on the use of anion-exchange resin and UTEVA extraction chromatography column. The isotope ratios were measured for two certified reference materials by using a VG Sector 54-30 thermal ionisation mass spectrometer in dynamic mode with Faraday cup and Daly ion counting system. Replicates of standard reference materials showed excellent analytical agreement with established values supporting the reliability and accuracy of the method. Precision of the ²³⁵U/²³⁸U ratio was achieved by a correction factor of 0.22% amu as a function of ion-beam intensity with sample loads of around 250?ng of U. The resulting reproducibility for standards and soil samples was better than 0.2% at two standard deviations (SD). Uranium isotopic compositions have been determined in several reference soil samples such as Buffalo river sediment, NIST 2704, river sediment SRM 4350b and ocean sediment NIST-4357 and a Chernobyl soil sample. There was a significant deviation from the natural uranium in comparison with Chernobyl soil samples.     

Influence of Isotope Effects on Product Polarizations of N(2D)+D2, N(2D)+H2 and N(2D)+HD Reactive Systems

To figure out the influence of isotope effect on product polarizations of the N(²D)+D₂ reactive system and its isotope variants, quasi-classical trajectory(QCT) calculation was performed on Ho’s potential energy surface(PES) of ²A″ state. Product polarizations such as product distributions of P(θ_r), P(φ_r) and P(θ_r,φ_r), as well as the generalized polarization-dependent differential cross sections(PDDCSs) were discussed and compared in detail among the four product channels of the title reactions. Both the intermolecular and intramolecular isotope effects were proved to be influential on product polarizations.     

QuEChERS-同位素稀释-液相色谱-高分辨飞行时间质谱法高通量筛查化妆品中86种糖皮质激素

建立了QuEChERS-同位素稀释-液相色谱-四极杆串联飞行时间质谱同时快速筛查化妆品中86种糖皮质激素(Glucocorticoids, GCs)的高通量方法.样品经乙腈提取,改进的QuEChERS法净化,待测物选用具有多重色谱保留机理的新型色谱柱Poroshell 120 PFP (100 mm×2.1 mm,2.7 μm),以0.2% (V/V)乙酸和乙腈为流动相进行梯度洗脱分离,在电喷雾离子源的正离子模式下建立了一级精确质量数及二级碎片离子质谱图数据库,无需标准品即可完成化妆品中86种GCs的全面筛查与确证.所有待测物在2~200 μg/L浓度范围内线性良好,相关系数均大于0.99, 3个添加水平的平均回收率为66.2%~112.8%,相对标准偏差(RSD)为4.6%~13.9%,检出限(LOD,S/N≥3) 为0.006~0.015 mg/kg,定量限(LOQ,S/N≥10)为0.02~0.05 mg/kg.本方法简便高效、定性可靠、定量准确,适用于化妆品中非法添加GCs的高通量筛查.