Demonstration of proton-transfer reaction time-of-flight mass spectrometry for real-time analysis of trace volatile organic compounds

A proton-transfer reaction mass spectrometer based on time-of-flight mass spectrometry is described. This instrument couples a radioactive ion source and drift tube with a reflectron time-of-flight mass spectrometer. Volatile organic compounds in the gas phase with concentrations at the parts per billion by volume level can be detected in a matter of seconds, and crucially, the multichannel data acquisition in TOF-MS means that this detection sensitivity is available in all mass channels simultaneously. The typical mass resolution (m/Deltam) is in excess of 1000. The performance of the instrument is demonstrated using urban air measurements and a linear response/calibration test.     

Derivatization of ethinylestradiol with dansyl chloride to enhance electrospray ionization: application in trace analysis of ethinylestradiol in rhesus monkey plasma

The extensive metabolism and administration of low doses of ethinylestradiol (EE) in preclinical animal species necessitates a sensitive analytical method to quantify the drug at low picogram-per-milliliter concentrations in biological matrixes. A highly sensitive and accurate method based on the derivatization of EE with dansyl chloride coupled with liquid chromatography/tandem mass spectrometry is described. The dansyl derivatization of EE introduced a basic secondary nitrogen into the molecule that was readily ionized in commonly used acidic HPLC mobile phases. The derivative showed an intense protonated molecular ion at m/z 530 under positive turbo ion spray ionization. The collision-induced dissociation of this ion formed a distinctive product at m/z 171, corresponding to the protonated 5-(dimethylamino)naphthalene moiety. The selected reaction monitoring, based on the m/z 530 --> 171 transition, was highly specific for EE, since no background signal was observed from blank plasma obtained from rhesus monkeys. The limit of detection, at a signal-to-noise ratio of 5, was 0.2 fg/mL EE spiked into blank plasma. This allowed for a lower limit of quantitation of 5 pg/mL using a 50-microL plasma sample and 10-microL injection of dansylated derivative into the CTC-PAL Leap autosampler coupled to a Sciex API 4000 mass spectrometer. Using fast-gradient liquid chromatography, the analyte peak eluted at 1.6 min. The validation results showed high accuracy (% bias < 4) and precision (% CV < 7.5) at broad linear dynamic ranges (0.005-20 ng/mL), using deuterated EE as internal standard. Therefore, the facile dansyl derivatization coupled with tandem mass spectral analysis allowed the development of a highly sensitive and specific method for quantitation of trace levels of EE in the plasma of rhesus monkeys dosed orally and intravenously with EE.     

Single particle nonlinear optical imaging of trace crystallinity in an organic powder

Microscopic characterization of crystallinity in powders can reveal information lost in ensemble-averaged measurements. Nonlinear optical imaging based on second harmonic generation (SHG) provides rapid and highly selective detection of individual chiral microcrystals, enabling insights into the fundamental mechanism of action for the observed crystallinity loss of an organic powder induced by mechanical grinding. Using griseofulvin as the model compound, the results from second order nonlinear optical imaging of chiral crystals (SONICC) compared favorably with those of powder X-ray diffraction (PXRD) over the linear dynamic range of the PXRD measurements. However, the SHG measurements demonstrated three decade improvements in linear dynamic range. The detection limit of SHG was estimated to be 4 ppm crystallinity in the powder. The rate of crystallinity loss induced by milling followed a first order process with a half-life of 15 ± 1 min. Recrystallization of cryomilled powder is ~40 times faster than that prepared by melt-quenched powder, suggesting that the disordered state obtained by exhaustive cryomilling appears to contain ordered domains that are larger than the critical nucleation size, but below the detection limit of SONICC. The presence of such domains provides a barrier-less nucleation source resulting in rapid crystallization, the kinetics of which depends only on crystal growth.     

Off-axis measurements of atmospheric trace gases by use of an airborne ultraviolet-visible spectrometer

An airborne UV-visible spectrometer, the Gas Analyzer Spectrometer Correlating Optical Differences, airborne version (GASCOD/A4pi) was successfully operated during the Airborne Polar Experiment, Geophysica Aircraft in Antarctica airborne campaign from Ushuaia (54 degrees 49' S, 68 degrees 18' W), Argentina in southern spring 1999. The instrument measured scattered solar radiation through three optical windows with a narrow field of view (FOV), one from the zenith, two from the horizontal, as well as actinic fluxes through 2pi FOV radiometric heads. Only a few airborne measurements of scattered solar radiation at different angles from the zenith are available in the literature. With our configuration we attempted to obtain the average line-of-sight concentrations of detectable trace gases. The retrieval method, based on differential optical absorption spectroscopy, is described and results for ozone are shown and compared with measurements from an in situ instrument as the first method of validation.     

Large strain analysis of an incompressible rubber cone contacting with a rigid conical socket

Summary Based on an incompressible three-dimensional model, the contact of a rubber cone with a rigid conical socket is analyzed by using the asymptotic method. Two parameters t and are introduced to attain the conclusion. The radial and angular distributions of stress and strain are obtained. The result shows that the stress field near the apex of the rubber cone is singular and possesses the singularity of order ln r, which differs from results in many previous studies. The elastic fields of the incompressible material model are quite different from those of the compressible material model.     

Inorganics in organics: quantification of organic phosphorus and sulfur and trace element speciation in natural organic matter using HPLC-ICPMS

A method is presented for the chemical characterization of natural organic matter (NOM). We combined reversed-phase chromatographic separation of NOM with high resolution inductively coupled plasma mass spectrometry. A desolvation technique was used to remove organic solvent derived from the preceding chromatographic separation. We applied our method to solid-phase extracted marine dissolved organic matter samples from South Atlantic and Antarctic surface waters. The method provided a direct and quantitative determination of dissolved organic phosphorus and sulfur in fractions of differing polarity and also allowed simultaneous speciation studies of trace elements. Dissolved organic carbon/phosphorus and carbon/sulfur ratios for the different chromatographic fractions of our two samples ranged between 341-3025 for C/P and 11-1225 for C/S. Differences in elemental distribution between the fractions were attributed to different biochemical environments of the samples. Sulfur was exclusively found in one hydrophilic fraction, while uranium showed a strong affinity to the hydrophobic fractions. Our method was designed to be easily adapted to other separation techniques. The elemental information will deliver valuable information for ultrahigh resolution molecular analyses.     

Inhomogeneous complexation of trace metals in water with organic nano-complexants

The complexation of heavy metals, such as Cd²⁺ and Ni²⁺, with organic complexants such as 1-(2-pyridylazo)-2-naphthol (PAN) and 1-(2-thiazolylazo)-2-naphthol (TAN) in water has been investigated. Under such conditions, both the reagents and the products form nano-particulates. These materials are important because their spectrum changes upon exposure to heavy metals and they may be used for design of new optical detectors. The kinetic schemes so far suggested for these complexation reactions are not valid for such experimental conditions, since they assume homogeneous behavior. We provide evidences to the inhomogeneous nature of these reactions. The complexation has been studied using TEM imaging, zeta-potentiometry, time-dependent particulate size analysis and time-dependent spectroscopy. Many of the experimental results are explained in terms of the nature of the nano-particulates of these two complexants. Several processes were identified, including crystal growing of the complexant, its reaction with metal ions in solution and on the surface area, chemical erosion of complexant crystallites and their decomposition, re-crystallization of the formed complexes and long term aggregation of both the complexant and the resulted complex. It was found that the needle-like nano-structures on the surface of the TAN particulates governs its reaction and particulate behavior. The known optimal complexation conditions, such as pH, and delay time are now understood in terms of the zeta-potential minima of the suspensions and in terms of the kinetic parameters. Also the interferences of some ions in the Ni–TAN complexation are now quantified and the kinetic data indicate the best delay time when the interfering effects are minimal.     

Failure analysis of the conical press-fit connections in a locomotive drive system

The nose-suspension drive designs with overhanging pinion are commonly applied in freight electrical locomotives because of simple, space-saving and cost-effective. The failures of conical press-fit connections in a nose-suspension drive system are analyzed in this paper. It was showed by the analysis that the crack on the inner conical surface of motor shaft is initiated by the combination of fretting and corrosion. Sharp oil groove edge and emergency of crack at the mouth of radial oil hole in pinion will accelerate the formation of fretting wear groove, and consequently the initiation of cracks. Coexist of tensile normal stress under the contact surface within the fretting zone will benefit the propagation of the fretting fatigue cracks.     

紫外荧光法测定有机液体化工品中痕量硫

针对有机液体化工品中痕量硫的检测难题,利用紫外荧光法建立了测定方法.考察了裂解温度和裂解氧流量对检测信号强度的影响,确定了最佳的实验条件.在添加浓度0.1ng/μL,0.2ng/μL,0.4ng/μL水平下,测得甲醇和甲苯中硫的回收率为88%～104%,重复测定几种常见的有机液体化工品中的硫含量,相对标准偏差在1.9%～6.8%范围内.结果表明该方法具有较好的准确度和精密度,可广泛用于有机液体化工品中痕量硫的测定.     

Mass profile monitoring in trace analysis by gas chromatography/mass spectrometry.

The advantages of gas chromatography/mass spectrometry (GC/MS) selected-ion monitoring (SIM) in the mass profile (MP) mode at medium mass resolving power were investigated for analyses requiring detection of low-picogram quantities of analytes in complex mixtures. The mass profile monitoring provides a certainty at least 10 times greater than that achieved by conventional GC/MS-SIM in the peak-top monitoring mode, and it can be operated at lower mass resolving power to compensate for the loss of sensitivity in the MP mode. The examination of mass profile peak shape, central mass shift, and sequential changes during GC elution not only reveals the presence of interfering compounds but also results in accurate mass measurement for those interferences. The latter feature takes the MP mode beyond the target mass analysis that GC/MS-SIM was originally designed for. This additional dimension of information is particularly useful for those complex and incompletely characterized matrices that are frequently encountered in environmental and biological sample analyses.     

The use of co-nomination analysis in real-time evaluation of an R&D programme

This article describes the application of co-nomination analysis, a technique designed to map the structure of a research community. The technique was used as part of the evaluation of the UK national information technology programme, which sponsors collaborative research between firms and between firms and universities. Co-nomination networks are based upon responses to questionnaires which researchers are asked to nominate other researchers whose work is similar or relevant to their own. Researchers nominated in the same response are presumed to be linked, and where these links occur with multiple frequency, the likelihood of their being significant is increased. The article describes the extension of a network which had been previously identified and compares the citation scores of researchers identified in the networks. It is concluded that the networks represented were realistic and a useful input to the evaluation. Industrial and government researchers with low citation scores were in some cases central to the networks, suggesting that co-nomination is useful in areas where publication is restricted or considered less important. Further development of the technique is planed.Order of names implies no precedence.     

Numerical analysis of flow pattern transition in a conical silo with ellipsoid particles

Gravity-driven discharge flow in conical silos is ubiquitous in manufacturing processes for numerous industries such as food, pharmaceutical and chemical industries, wherein flow pattern is the key topic to be studied. In this work, discrete element method was used to study discharge flow behaviors in a special conical silo. This work aims to understand the dynamic evolution of discharge flow pattern and establish methods for regional determination of flow pattern transition. The results indicated that both mass flow and funnel flow patterns coexist in the silo at the initial stage of discharge, and there is a definite transition process from mass flow to funnel flow. Furthermore, the flow pattern transition is revealed by the change in discharge flow characteristics. Specifically, the change in force acting on particles leads to the change of particle orientation and particle velocity field, macroscopically resulting in the flow pattern transition. Finally, based on the kinetic stress field and shear rate, the height and radial region of flow pattern transition were determined, respectively. Understanding of the flow pattern transition is useful to the design, scale-up and optimization of silos and similar structural devices.     

Tunable ultraviolet laser-induced fluorescence detection of trace plastics and dissolved organic compounds in water

We developed a tunable (220-285-nm) UV and fixed 266-nm laser-induced fluorescence (LIF) system using a spectrometer and a cooled CCD imaging detector to measure the excitation-emission matrix spectra of various compounds in water, including quinine sulfate and plastic compound bisphenol-A. The LIF instrument was used for the fast, nonspecific determination of trace amounts of dissolved organic compounds present in natural water supplies and various brand name bottled distilled water and bottled drinking water. Plastic-related compounds that leached out of plastic utensils and containers were also detected with this instrument. The sensitivity of the system was approximately 1-2 orders of magnitude better than that for a commercial system.     

Preparation of highly concentrated and stable suspensions of silver nanoparticles by an organic base catalyzed reduction reaction

Highly concentrated and stable suspensions of silver nanoparticles have been synthesized by chemical reduction from silver nitrate in a formaldehyde reductant using an organic base, triethylamine, as the reaction promoter. In this reaction, a low molecular weight organic compound, thiosalicylic acid (TSA), was used as the protecting agent. The average size of the silver nanoparticles prepared from this method was less than 10 nm, which allowed low-temperature sintering of the metal. The suspensions were further stabilized by the addition of excessive triethylamine, which forms an amine salt with TSA. A 50 wt%, stable suspension has been prepared. The suspensions of silver nanoparticles prepared by this method are free from any metal ion contamination, and are suitable for use in semiconductor industries.     

Sample preparation techniques in trace element analysis of water

Sample preparation techniques for the analysis of water for trace elements using X-ray emission spectroscopy are described.Fresh water samples for the analysis of transition metals were prepared by complexation with ammonium-pyrrolidine-dithiocarbamate (APDC) and filtering through a membrane filter. Analyses of water samples for halogenes was done on samples prepared by precipitation with AgNO₃ and subsequent filtration. Two techniques for seawater preparation for uranium determination are described, viz. precipitation with APDC in the presence of iron (II) as a carrier and complexation with APDC followed with adsorption on activated carbon.In all cases trace element levels at 10^?3 μg/g were measured.