Study of nanoscale photopolymerized fullerene clusters in solution droplets using an ultrasonic nebulizer unit

In a designed and developed ultrasonic nebulizer system for obtaining macroscopic-quantity photopolymerized fullerene (C60) clusters, a C60 solution was vaporized to several micro-sized droplets in vacuum, resulting in the formation of C60 aggregates by evaporating the solvent (toluene). The system was invented to produce nanoscale photopolymerized carbon clusters through the irradiation of ultraviolet (UV) light on the C60 aggregates in vacuum. The products, photopolymerized C60 clusters obtained from the system using UV-visible (UV-Vis) absorption and high-performance (or high-pressure) liquid chromatography (HPLC) spectra, were characterized. Compared with the non-irradiating C60 solution, the UV-Vis absorption spectrum of the irradiated C60 solution was drastically decreased, especially at lambda = 335 nm and in the visible region from lambda = 450-650 nm. As such, the UV-Vis absorption spectra provide information about the polymerization of C60 molecules. These photopolymerized C60 clusters can be detected as having a heavy molecular mass order through the HPLC system, and the C60 and photopolymerized C60 cluster can be extracted from the trapped solution on the molecular mass. Although there is a possibility that the products include various forms of C60 clusters, the results suggest that the products obtained from the system using a vaporizer establish a new method of obtaining macroscopic-quantity C60 clusters.     

Fluorescence correlation spectroscopy: an efficient tool for measuring size, size-distribution and polydispersity of microemulsion droplets in solution

Fluorescence correlation spectroscopy (FCS) is an ideal tool for measuring molecular diffusion and size under extremely dilute conditions. However, the power of FCS has not been utilized to its best to measure diffusion and size parameters of complex chemical systems. Here, we apply FCS to measure the size, and, most importantly, the size distribution and polydispersity of a supramolecular nanostructure (i.e., microemulsion droplets, MEDs) in dilute solution. It is shown how the refractive index mismatch of a solution can be corrected in FCS to obtain accurate size parameters of particles, bypassing the optical matching problem of light scattering techniques that are used often for particle-size measurements. We studied the MEDs of 13 different W(0) values from 2 to 50 prepared in a ternary mixture of water, sodium bis(2-ethylhexyl) sulfosuccinate (AOT), and isooctane, with sulforhodamine-B as a fluorescent marker. We find that, near the optical matching point of MEDs, the dynamic light scattering (DLS) measurements underestimate the droplet sizes while FCS estimates the accurate ones. A Gaussian distribution model (GDM) and a maximum-entropy-based FCS data fitting model (MEMFCS) are used to analyze the fluorescence correlation curves that unfold Gaussian-type size distributions of MEDs in solution. We find the droplet size varies linearly with W(0) up to ~20, but beyond this W(0) value, the size variation deviates from this linearity. To explain nonlinear variation of droplet size for W(0) values beyond ~20, we invoke a model (the coated-droplet model) that incorporates the size polydispersity of the droplets.     

Protocol for an electrospray ionization tandem mass spectral product ion library: development and application for identification of 240 pesticides in foods

Modern determination techniques for pesticides must yield identification quickly with high confidence for timely enforcement of tolerances. A protocol for the collection of liquid chromatography (LC) electrospray ionization (ESI)-quadruple linear ion trap (Q-LIT) mass spectrometry (MS) library spectra was developed. Following the protocol, an enhanced product ion (EPI) library of 240 pesticides was developed by use of spectra collected from two laboratories. A LC-Q-LIT-MS workflow using scheduled multiple reaction monitoring (sMRM) survey scan, information-dependent acquisition (IDA) triggered collection of EPI spectra, and library search was developed and tested to identify the 240 target pesticides in one single LC-Q-LIT MS analysis. By use of LC retention time, one sMRM survey scan transition, and a library search, 75-87% of the 240 pesticides were identified in a single LC/MS analysis at fortified concentrations of 10 ng/g in 18 different foods. A conventional approach with LC-MS/MS using two MRM transitions produced the same identifications and comparable quantitative results with the same incurred foods as the LC-Q-LIT using EPI library search, finding 1.2-49 ng/g of either carbaryl, carbendazim, fenbuconazole, propiconazole, or pyridaben in peaches; carbendazim, imazalil, terbutryn, and thiabendazole in oranges; terbutryn in salmon; and azoxystrobin in ginseng. Incurred broccoli, cabbage, and kale were screened with the same EPI library using three LC-Q-LIT and a LC-quadruple time-of-flight (Q-TOF) instruments. The library search identified azoxystrobin, cyprodinil, fludioxinil, imidacloprid, metalaxyl, spinosyn A, D, and J, amd spirotetramat with each instrument. The approach has a broad application in LC-MS/MS type targeted screening in food analysis.     

A strategy for the determination of enzyme kinetics using electrospray ionization with an ion trap mass spectrometer.

A simple and rapid means of enzyme kinetic analysis was achieved using electrospray ionization mass spectrometry and a one-point normalization factor. The model system used, glutathione S-transferase from porcine liver, is a two-substrate enzyme catalyzing the conjugation of glutathione with a variety of compounds containing an electrophilic center. An internal standard that is structurally similar to the product was added to the reaction quench solution, and a single-point normalization factor was used to determine the product concentration without the need of a calibration curve. Kinetic parameters, such as Km, Vmax and Ki (for thyroxine), obtained by electrospray mass spectrometry agreed with those obtained from traditional UV-vis spectroscopy, and competitive vs noncompetitive inhibition reactions could be delineated via mass spectrometry. These results suggest that our method can be applied to enzymatic processes in which spectrophotometric or spectrofluorometric assays are not feasible or when the relevant substrates do not incorporate chromophores or fluorophores. This new method is competitive with traditional UV assays in that it is facile and it involves very little analysis time.     

Nonlinear signal response in electrospray mass spectrometry: implications for quantitation of arsenobetaine using stable isotope labeling by liquid chromatography and electrospray Orbitrap mass spectrometry

Isotope amount ratio measurements by electrospray ionization mass spectrometry show large systematic biases. Moreover, the signal ratio response can vary nonlinearly with respect to the amount ratio depending on the concentration of the analyte or coeluting matrix components, among other things. Since isotope dilution relies inherently on the linearity of response, accurate quantitation is then more difficult to achieve. In this study, we outline a method to eliminate the quantitation errors due to the effects of the nonlinear signal response. The proposed approach is a hybrid of the method of standard additions and isotope dilution allowing correction for nonlinear trend. As a proof of concept, determination of arsenobetaine content in fish tissue was performed using liquid chromatography coupled with a linear quadrupole ion trap (LTQ) Orbitrap mass spectrometer. The nonlinear isotope dilution method could, in principle, be applied to correct isotope ratio measurement biases in popular relative quantitation methods of biomolecules such as stable isotope labeling by amino acids in cell culture (SILAC), isotope-coded affinity tag (ICAT), or isobaric tags for relative and absolute quantification (iTRAQ).     

Measuring the size and charge of single nanoscale objects in solution using an electrostatic fluidic trap

Measuring the size and charge of objects suspended in solution, such as dispersions of colloids or macromolecules, is a significant challenge. Measurements based on light scattering are inherently biased to larger entities, such as aggregates in the sample, because the intensity of light scattered by a small object scales as the sixth power of its size. Techniques that rely on the collective migration of species in response to external fields (electric or hydrodynamic, for example) are beset with difficulties including low accuracy and dispersion-limited resolution. Here, we show that the size and charge of single nanoscale objects can be directly measured with high throughput by analysing their thermal motion in an array of electrostatic traps. The approach, which is analogous to Millikan's oil drop experiment, could in future be used to detect molecular binding events with high sensitivity or carry out dynamic single-charge resolved measurements at the solid/liquid interface.     

Evidence for an early onset of endogenous alcohol production in bodies recovered from the water: implications for studying alcohol and drowning

Endogenous alcohol production can increase the blood alcohol concentration (BAC) of drowning victims following submersion and confound epidemiological studies of the role of alcohol. This study seeks to determine how soon after a drowning death a victim's BAC is influenced by post-mortem alcohol production. The drop in mean lung weight that occurs over time in the water was hypothesized to serve as a proxy for the time course of decomposition, and thus provide an empirical measure to determine how soon after death to first suspect endogenous alcohol. The autopsy lung weights of 562 previously healthy males who drowned were compared across six submersion time groups (0-11.9, 12-23.9, 24-47.9, 48-95.9, 96-167.9 and >or=168 h) and two times of year (winter and non-winter). The hypothesis that a drop in lung weight is sensitive to the time course of decomposition was supported by (1). a statistically significant drop in mean lung weight that occurred 12-23.9 h post-submersion in the non-winter months, but not until 96-167.9 h in the colder winter months; and (2). a significant drop in lung weight was not observed in the group of cases with zero BAC. With a parallel finding that an increase in the proportion of cases with a positive BAC first occurred at the 12-23.9 h submersion group during the warmer non-winter months, we concluded that production of alcohol can occur in bodies recovered from the water as early as 12 h after death. Because excluding drownings with submersion durations greater than 12 h would exclude almost half of our cases from epidemiological studies of alcohol and drowning, additional evidence from the forensic literature was used to develop an adjustment procedure to account for endogenous alcohol production for submersion times of up to 1 week.     

Selective detection of proteins in mixtures using electrospray ionization mass spectrometry: influence of instrumental settings and implications for proteomics

We studied the effects of electrospray mass spectrometric instrumental settings on the relative and absolute detection of individual proteins in a five-component mixture. Conditions that were effective for a given protein could be very poor for the others, and vice versa, such that to a good approximation it was possible to find conditions for selective detection of individual proteins in a complex mixture without prior analytical separation. Some of these could be rationalized on the basis of the known biophysical properties of the individual proteins. The ability to vary the conditions of a mass spectrometric detection method on-line provides an important degree of freedom for the selective detection, and hence discrimination, of individual proteins and peptides in complex mixtures and has implications in proteomics, in particular with respect to top-down strategies for proteomic characterizations.     

Space charge effects and dynamic interactions in the case of a broad and intense ion beam bombarding an insulated substrate

A small single grid ion gun system, isolated by a quartz tube, was investigated. The dependence of the potential of the floating substrates was measured, and its dependence on grid voltage and pressure was determined. This potential could be controlled by changing the parameters of the ion gun. This seems to be a new possibility for controlled deposition of insulating materials with ion beams of low energy. And it explains results which were obtained in deposition of diamond-like carbon films on insulating substrates.     

Design of an i.v. formulation of an unstable prodrug candidate for prostate cancer treatment: solution chemistry of N-(glutaryl-hyp-ala-ser-cyclohexylglycyl-gln-ser-leu)-doxorubicin

The chemical degradation of N-(glutaryl-hyp-ala-ser-cyclohexylglycyl-gln-ser-leu)-doxorubicin (henceforth referred to as doxorubicin peptide conjugate 1) was studied in buffered aqueous solution. The pH-rate profile of degradation shows that the doxorubicin conjugate is most stable between pH 5 and 6. The dependence of log k_obsd on pH in acidic medium is characteristic of specific acid-catalysis of the sugar hemiaminal of 1 (as in the case of doxorubicin). Isolation of degradates and structural determination shows that the degradation at lower pH values yields the water-insoluble aglycone doxorubicinone, supporting the mechanism of acid-catalyzed loss of the amino sugar. At pH higher than 5, a more complicated degradation pattern is observed, including the loss of the amino sugar and the aromatization of the saturated ring to give 7,8-dehydro-9,10-desacetyldoxorubicinone as one of the major products. Around the pH of maximum stability in solution, the rate of degradation of 1 is significantly greater than that for doxorubicin, which rules out the formulation of a room temperature solution product with a sufficiently long shelflife for market use. Design of a stable lyophilized formulation for sterile reconstitution based on the physicochemical properties of 1 is described.     

Pulsed hydrogen/deuterium exchange MS/MS for studying the relationship between noncovalent protein complexes in solution and in the gas phase after electrospray ionization

Electrospray ionization mass spectrometry (ESI-MS) has become a standard method for monitoring noncovalent protein-protein interactions. Studies employing this approach tend to operate on the premise that the ionic species observed in the mass spectrum directly reflect the corresponding solution-phase protein quaternary structures. However, dissociation or clustering events taking place during ESI may lead to disparities between the ions observed in the mass spectrum and the protein binding state in bulk solution. Recognizing the occurrence of dissociation or clustering artifacts is not straightforward, leading to possible ambiguities in the interpretation of ESI-MS data. This work employs on-line pulsed hydrogen-deuterium exchange (HDX) for probing the origin of various species in the ESI mass spectrum of hemoglobin. In addition to the canonical hemoglobin tetramer, ESI-MS reveals the presence of monomers, dimers, hexamers, and octamers. Tandem mass spectrometry (MS/MS) is used for extracting HDX levels in a subunit-specific manner. Dimeric species exhibit exchange levels that are significantly above those of the tetramer. Monomeric hemoglobin subunits are labeled to an even greater extent. This HDX pattern implies that monomers and dimers do not represent dissociation artifacts generated during ESI. Instead, they are derived from preexisting solution-phase structures. In contrast, hexamers and octamers exhibit HDX levels that resemble those of the tetramer, thus identifying these larger species as nonspecific clustering artifacts. Overall, it appears that the pulsed HDX MS/MS approach introduced in this work represents a widely applicable tool for deciphering the relationship between ESI mass spectra and protein quaternary structures in solution.     

定量包装商品净含量计量检验方法的探讨

为保证定量包装商品净含量计量检验结果的统一性、有效性和准确性,依据JJF 1070-2005《定量包装商品净含量计量检验规则》,对影响定量包装商品净含量检验结果的不确定度的主要来源和检验的关键点进行分析,找出每种检验方法中影响净含量检验结果的测量不确定度,为今后科学地计量检验定量包装商品净含量奠定基础。     

Polarity change in the tribo-charge of particles with and without an initial charge

Polarity change in the electrostatic charge of particles impacting on a rotating metal target has been investigated. Experimental results are discussed from the viewpoint of the relationship between the initial charge of particles and the polarity of the tribo-charge. Experimental apparatus, where the initial charge is hardly generated before impacting on the rotating metal target, has been developed using a unit of coaxial dual tubes. It is found that the current generated from the target decreases with time and the tendency depends on the impact angle θ. In particular, the polarity of the current generated by the tribo-charge changes from positive to negative for θ > 75°. A sharper decrease in the current occurs for a higher normal component of impact velocity. A particle feeding system that can change the initial charge of particles has been contrived and it is set between the glass hopper and the unit of the coaxial dual tubes. This equipment enable us to obtain the fact that for θ = 48° (no polarity change), the current decreases linearly with increasing the initial charge, while for θ = 86° (polarity change occurs) it increases with increasing the initial charge and then approaches a certain constant value for a higher initial charge. Both minor and major axes of scars, which are formed by impacting particles on a target, are measured for the case that the polarity change occurs and the apparent area of each scar is calculated as an ellipse. From the results, this is found that the area increases with increasing the impact angle and the tribo-charge increases with the area. Therefore, this suggests that the apparent contact area controls the tribo-charge for the case where the polarity change occurs.     

Investigation of coated droplets in an optical trap: Raman-scattering, elastic-light-scattering, and evaporation characteristics

Single optically levitated microparticles were investigated by Raman spectroscopy. The particles were composed of di-octyl-phthalate (DOP) and glycerol; these substances are not mixable and form a two-phase droplet. Measurements of the Raman spectrum confirm the formation of droplets containing both chemical species. The spectra show strong input and output structural resonances as expected. If the particle is in resonance, the field inside the particle is enhanced, and most of the inelastically scattered light is emitted from molecules close to the droplet rim. If the particle does not fulfill the resonance condition, the contribution of an individual molecule to the Raman scattering does not depend strongly on the radial position of this molecule. On this basis, the radial distribution of the two components inside the evaporating droplet was determined by time-dependent measurements of the Raman spectrum. Furthermore, elastic-light scattering and the evaporation characteristics of the particles were investigated.     

Probing interfacial chemistry of single droplets with field-induced droplet ionization mass spectrometry: physical adsorption of polycyclic aromatic hydrocarbons and ozonolysis of oleic acid and related compounds

The recently developed technique of field-induced droplet ionization (FIDI) is applied to study interfacial chemistry of a single droplet. In a new variation of the FIDI method, 1-2-mm-diameter droplets hang from a capillary and undergo heterogeneous reactions between solution-phase analytes and gas-phase species. Following a specified reaction time, the application of a high electric field induces FIDI in the droplet, generating fine jets of highly charged progeny droplets that are characterized by mass spectrometry. Sampling over a range of delay times following exposure of the droplet to gas-phase reactants, the spectra yield the temporal variation of reactant and product concentrations. We illustrate the technique with three examples: the adsorption of the polycyclic aromatic hydrocarbon naphthalene into a water-methanol droplet, the ozonolysis of oleic acid, and localization of the carbon-carbon double bond within a lysophosphatidic acid. Gas-phase naphthalene reacts with 80% methanol-20% water droplets containing 100 microM silver nitrate. Positive ion mass spectra show increasing concentrations of silver ion-naphthalene adducts as exposure times increase. To examine the ozonolysis of organic molecules, gas-phase ozone generated by a mercury pencil-style lamp reacts with either 10 microM oleic acid or 100 microM oleoyl-L-alpha-lysophosphatidic acid (LPA; 18:1). Negative ion spectra from the ozonolysis of oleic acid show azelaic acid and 9-oxononanoic acid as the principle reaction products. Ozonolysis products from LPA (18:1) unambiguously demonstrate the double bond position in the original phospholipid.     

A note on: an optimal batch size for an imperfect production system with quality assurance and rework

In [Ojha, D., Sarker, B.R., and Biswas, P., 2007. An optimal batch size for an imperfect production system with quality assurance and network. International Journal of Production Research, 45 (14), 3191–3214] three models are introduced in the context of imperfect production systems. By analysing the proposed models we identify some problems. In particular we focus on six issues of the models developed in Ojha et al. and propose some modifications. All corrections are presented in detail and the numerical example of Ojha et al. is used to show the influence of the issues addressed in this paper.     

Determination of colchicine residues in sheep serum and milk using high-performance liquid chromatography combined with electrospray ionization ion trap tandem mass spectrometry

Colchicine is a naturally occurring alkaloid used in human and veterinary medicine. It shows genotoxicity in in vitro and in vivo systems even at low concentrations. Therefore, no ADI has been established, and colchicine has been included in Annex IV of Council Regulation (EEC) No. 2377/90. No abuse of this drug in intensive livestock farming has yet been reported. However, there may be a natural route of entry for this compound into the food chain when Colchicum autumnale is consumed by animals kept outdoors. To address this concern, we developed and validated a highly sensitive and selective quantitative LC-ESI-MS-MS method for the detection of colchicine in sheep serum and milk. For sample pretreatment, all samples were liquid-liquid extracted with phosphate buffer (pH 8.0) and dichloromethane. LC separation was carried out on an RP C18 column employing a 0.5% formic acid/acetonitrile gradient system. The recoveries in both matrixes at a concentration range from 0.0005 to 1 mg/L were >80% with RSDs of <10%. The applicability of the method was demonstrated in serum and the corresponding milk samples from Albanian sheep. After exposure to C. autumnale, the animals showed clinical signs of intoxication. Significant concentrations (up to 1 mg/L) of the drug were found in serum as well as in milk samples.     

The numerical solution of boundary-value problems for an elastic body with an elliptic hole and linear cracks

Using the boundary-element method which is a combination of a fictitious load and a displacement discontinuity, numerical solutions are obtained for two-dimensional (plane deformation) boundary-value problems for the elastic equilibrium of infinite and finite homogeneous isotropic bodies having elliptic holes with cracks and cuts of finite length. Using the method of separation of variables, the boundary-value problem is solved in the case of an infinite domain containing an elliptic hole with a linear cut on whose contour the symmetry conditions are fulfilled.