Preparation of targets on thin backings with a centrifugal precipitation method

The preparation of various powder-material targets in thicknesses of 0.1 to 15 mg/cm² on backings of aluminium, gold, and carbon as thin as 0.2 μm using a centrifugal precipitation method is described. In this method, collodion in acetone is the suspension agent for the target materials. In most cases, the yield of the method is 80%. The amount of residual collodion in the target is about 5% and can be decreased to about 1% by heating.     

Chloride stress corrosion cracking of precipitation hardening S.S. impellers in centrifugal compressor. Laboratory investigations and corrective actions

17-4 PH, precipitation hardening stainless steel (ASTM A 705 Grade 630), is widely employed in several industrial fields because of its favourable combination of excellent mechanical properties and good corrosion resistance. An important application of 17-4 PH is the construction of centrifugal compressor impellers, where performance benefits from the steel's high mechanical resistance even when it is necessary to limit hardness, for example, as per NACE MR0175, to avoid devastating sulphide stress cracking phenomena in sour environments. Nevertheless, there has been a case in which impellers made of 17-4 PH have been subject to failures. It was a centrifugal compressor employed in a gas lifting service in which the fluid entrained water with a high level of salinity. Laboratory failure analysis attributed the damage to chloride stress corrosion cracking phenomena and was followed by a study on the behaviour of 17-4 PH in chloride-rich environments and on the action to take to avoid damage causing forced outages and loss of production.     

Identification of polar toxicants in industrial wastewaters using toxicity-based fractionation with liquid chromatography/mass spectrometry.

An efficient and novel method for the identification of toxic compounds in industrial wastewater was developed. In the first step, the samples collected were tested for toxicity using the recently developed ToxAlert 10 system based upon luminescence inhibition of freeze-dried Vibrio fischeri. In the second step, sequential solid-phase extraction (SSPE) and liquid chromatography/mass spectrometry (LC/MS) for compound identification were employed to isolate and identify compounds in the waters. Average recoveries ranging from 72 to 95% were obtained using the SSPE methodology for ubiquitous analytes such as poly(ethylene glycol)s, nonylphenol and alcohol polyethoxylates, phenols, linear alkylbenzenesulfonates, and benzene- and naphthalenesulfonates. In the third step, all the extracts obtained after SSPE followed by LC/MS identification were tested again with the ToxAlert system. The procedure was applied to influent and effluent samples of a sewage treatment plant (STP) and to a raw tannery effluent that constitutes the main type of influent in the receiving waters of the STP. This method has shown that, despite the complexity of the untreated tannery wastewaters with an average total organic carbon (TOC) value of 1960 mg of C/L, the biological treatment of the STP eliminates compounds that inhibit luminiscence of V. fischeri. In the final step, the chemical toxicity of the tentatively identified chemicals was tested to identify the toxicants in the waters. Comparison of the toxicities of the sample, the extracts, and individual components has shown that diverse classes of pollutants were responsible for toxicity, as all fractions of toxic samples gave significant bioluminescence inhibition values. Toxicity of the two intermediate-polarity SSPE fractions was attributed to alcohol ethoxylates, nonylphenol ethoxylates, bis(2-ethylhexyl)phthalate, and linear alkylbenzenesulfonates. In the most nonpolar and most polar fractions, identification of the compounds responsible for toxicity was unclear. By the toxicity-based fractionation, followed by LC/MS methodology, it was feasible to identify between 1.4 and 7.5% of the TOC, thus expanding the number of toxicants identified in these complex wastewaters as compared to those identified by conventional gas chromatography/mass spectrometric (GC/MS) methods. When artificial water samples were reconstituted using similar concentrations of the chemicals detected in the wastewaters, nonsynergetic toxicity effects were observed for all analytes with the exception of 2,6-naphthalenedisulfonate (2,6-NPS), which promoted the bioluminescence inhibition. The toxicity-directed identification was successful for the STP's samples and showed 1400 times higher toxicity for the raw tannery wastewaters as compared to the mixed industrial and domestic wastewaters by applying the Weibull model.     

Study of flow fractionation characteristics of magnetic chromatography utilizing high-temperature superconducting bulk magnet

We present numerical simulation of separating magnetic particles with different magnetic susceptibilities by magnetic chromatography using a high-temperature superconducting bulk magnet. The transient transport is numerically simulated for two kinds of particles having different magnetic susceptibilities. The time evolutions were calculated for the particle concentration in the narrow channel of the spiral arrangement placed in the magnetic field. The field is produced by the highly magnetized high-temperature superconducting bulk magnet. The numerical results show the flow velocity difference of the particle transport corresponding to the difference in the magnetic susceptibility, as well as the possible separation of paramagnetic particles of 20 nm diameter.     

Method for analysis of polar volatile trace components in aqueous samples by gas chromatography

A new method has been developed for direct analysis of volatile polar trace compounds in aqueous samples by gas chromatography. Water samples are injected onto a short packed precolumn containing anhydrous lithium chloride. A capillary column is coupled in series with the prefractionation column for final separation of the analytes. The enrichment principle of the salt precolumn is reverse to the principles employed in conventional methods such as SPE or SPME in which a sorbent or adsorbent is utilized to trap or concentrate the analytes. Such methods are not efficient for highly polar compounds. In the LiCl precolumn concept, the water matrix is strongly retained on the hygroscopic salt, whereas polar as well as nonpolar volatile organic compounds show very low retention and are eluted ahead of the water. After transfer of the analytes to the capillary column, the retained bulk water is removed by backflushing the precolumn at elevated temperature. For direct injections of 120 microL of aqueous samples, the combined time for injection and preseparation is only 3.5 min. With this procedure, direct repetitive automated analyses of highly volatile polar compounds such as methanol or tetrahydrofuran can be performed, and a limit of quantification in the low parts-per-billion region utilizing a flame ionization detector is demonstrated.     

Study of flow fractionation characteristics of magnetic chromatography utilizing high-temperature superconducting bulk magnet

Abstract

We present numerical simulation of separating magnetic particles with different magnetic susceptibilities by magnetic chromatography using a high-temperature superconducting bulk magnet. The transient transport is numerically simulated for two kinds of particles having different magnetic susceptibilities. The time evolutions were calculated for the particle concentration in the narrow channel of the spiral arrangement placed in the magnetic field. The field is produced by the highly magnetized high-temperature superconducting bulk magnet. The numerical results show the flow velocity difference of the particle transport corresponding to the difference in the magnetic susceptibility, as well as the possible separation of paramagnetic particles of 20 nm diameter.     

Column precipitation chromatography: an approach to quantitative analysis of eigencolloids

A new column precipitation chromatography (CPC) technique, capable of quantitatively measuring technetium eigencolloids in aqueous solutions, is presented. The CPC technique is based on the destabilization and precipitation of eigencolloids by polycations in a confined matrix. Tc(IV) colloids can be quantitatively determined from their precipitation onto the CPC column (separation step) and their subsequent elution upon oxidation to pertechnetate by peroxide (elution step). A clean-bed particle removal model was used to explain the experimental results.     

Correction for particle-wall interactions in the separation of colloids by flow field-flow fractionation

In the characterization of materials by field-flow fractionation (FFF), the experienced analyst understands the importance of incorporating additives in the carrier liquid that minimize or eliminate interactions between the analyte and accumulation wall, particularly in aqueous systems. However, as FFF is applied to more difficult samples, such as those with high surface energies, it is increasingly difficult to find additives that completely eliminate particle-wall interactions. Furthermore, the analyst may wish to use specific conditions that preserve the high surface energy of particles, to study their interaction with other materials through their behavior in the FFF channel. With this in mind, Williams and co-workers developed a model that quantifies the effect of particle-wall interactions in FFF using an empirically determined interaction parameter. In this work, the model is evaluated for the application of flow FFF in carrier liquids of low ionic strength, where particle-wall interactions are magnified. The retention of particles ranging in size from 64 to 1000 nm is measured using a wide range of field strengths and retention levels. The model is found to be generally valid over the entire range, except for minor discrepancies at lower levels of retention. Although retention levels are dramatically affected by particle-wall interactions, the point of steric inversion (500 nm), where the size-based elution order reverses, is not affected. When particle-wall interactions are not accounted for, they lead to a bias in particle sizes calculated from standard retention theory of up to 70%. The model can also be used to refine the measurement of channel thickness, which is important for the accurate conversion of retention parameters to particle sizes. In this work, for example, errors in channel thickness led to systematic errors on the order of 10% in particle diameter.     

The use of analytic surfaces for the design of centrifugal impellers by computer graphics

This paper shows how analytic surfaces can be used to define the vanes of an impeller of a centrifugal compressor. The analysis has been given of a cubic-linear patch for representing three-dimensional geometries. An example has shown how this type of patch can be successfully used to model the geometry of centrifugal or mixed flow impellers having 'swept back vanes at the outlet. The analysis has been programmed for the Atlas computer at the Computer Aided Design Centre (CADC), Cambridge and set up in such a way that the designer can examine systematically a range of impeller shapes.     

Size fractionation of gas-filled microspheres by flotation

A dynamic model has been developed for the size fractionation process of gas-filled microspheres by flotation. The aim of this dynamic model is to control the fractionation process in an Nycomed Imaging AS Infoson^™ production plant. A general population balance is established for the dispersed phase that is later simplified for the specific particle suspension and process equipment used. This dynamic model has been tested against experimental data and shows a good correlation between the predicted and measured values. This paper describes both the physical phenomena and the modeling method.     

Preparative enantiomer separation of dichlorprop with a cinchona-derived chiral selector employing centrifugal partition chromatography and high-performance liquid chromatography: a comparative study

A countercurrent chromatography protocol for support-free preparative enantiomer separation of the herbicidal agent 2-(2,4-dichlorphenoxy)propionic acid (dichlorprop) was developed utilizing a purposefully designed, highly enantioselective chiral stationary-phase additive (CSPA) derived from bis-1,4-(dihydroquinidinyl)phthalazine. Guided by liquid-liquid extraction experiments, a solvent system consisting of 10 mM CSPA in methyl tert-butyl ether and 100 mM sodium phosphate buffer (pH 8.0) was identified as a suitable stationary/mobile-phase combination. This solvent system provided an ideal compromise among stationary-phase retention, enantioselectivity, and well-balanced analyte distribution behavior. Using a commercial centrifugal partition chromatography instrument, complete enantiomer separations of up to 366 mg of racemic dichlorprop could be achieved, corresponding to a sample load being equivalent to the molar amount of CSPA employed. Comparison of the preparative performance characteristics of the CPC protocol with that of a HPLC separation using a silica-supported bis-1,4-(dihydroquinidinyl)phthalazine chiral stationary phase CSP revealed comparable loading capacities for both techniques but a significantly lower solvent consumption for CPC. With respect to productivity, HPLC was found to be superior, mainly due to inherent flow rate restrictions of the CPC instrument. Given that further progress in instrumental design and engineering of dedicated, highly enantioselective CSPAs can be achieved, CPC may offer a viable alternative to CSP-based HPLC for preparative-scale enantiomer separation.     

Mouse embryonic stem cell sorting for the generation of transgenic mice by sedimentation field-flow fractionation

Mouse embryonic stem (ES) cells are an important tool for generation of transgenic mice and genetically modified mice. A rapid and efficient separation of ES cells that respects cell integrity, viability, and their developmental potential while also allowing purified ES fraction collection under sterile conditions might be of great interest to facilitate the generation of chimeric animals. In this study, we demonstrated for the first time the effectiveness of a sedimentation field-flow fractionation (SdFFF) cell sorter to provide, with a characteristic DNA content, a purified ES cell fraction and with a high in vivo developmental potential to prepare transgenic mice by generation of chimeras having a high percentage of chimerism.     

Compositional effects in the retention of colloids by thermal field-flow fractionation

The retention of polystyrene and silica colloids that have been chemically modified is measured in several aqueous carrier liquids. Retention levels are governed by particle size and composition but are also sensitive to subtle changes in the carrier. Size-based selectivities are higher in aqueous carriers compared to acetonitrile. In aqueous carriers, retention varies dramatically with the nature of the additive, and for a given additive, retention increases with ionic strength, regardless of modifications to the particle surface. The role played by electrostatic effects in retention is studied by varying the ionic strength of the carrier, estimating electrical double layers, determining particle-wall interaction parameters, and calculating the coefficients of mass diffusion and thermal diffusion. Although electrostatic phenomena can affect mass diffusion and particle-wall interactions in carriers of low ionic strength (<10(-3) M), such effects are not great enough to explain the dependence of retention on ionic strength. Therefore, thermal diffusion must be affected directly. Thermal diffusion is found to increase with pH, and at a given pH with the surface tension of the suspended particle. Finally, while the addition of the surfactant FL-70 generally decreases retention, greater retention levels can ultimately be achieved with FL-70 because larger temperature gradients can be used without particle adsorption to the accumulation wall.     

Bacteria sorting by field-flow fractionation. Application to whole-cell Escherichia coil vaccine strains

Sorting and quantification of deactivated bacteria is an important way of quality control for whole-cell bacterial vaccines. In general, surface features of deactivated bacteria used for whole-cell bacterial vaccines affect the immunoresponse to bacteria-associated antigens. Enumeration of bacteria is also an important process development parameter for these vaccines. Field-flow fractionation (FFF) was previously applied to the separation of bacteria. For the first time, FFF is used for sorting bacteria strains of the same species on the basis of differences in bacterial membrane characteristics. Two FFF techniques, gravitational FFF (GrFFF) and asymmetrical flow FFF (AsFIFFF), are shown to be able to fractionate, distinguish, and quantify different deactivated Escherichia coli strains used for vaccines. E. coli can differ in the presence of fimbriae on the bacterial membrane. Fimbriae affect E. coli pathology and thus the use of E. coli for vaccines. GrFFF and AsFIFFF are able to fractionate fimbriated/ nonfimbriated cells in mixtures of different strains. While GrFFF is characterized by low cost and simplicity, As-FIFFF shows a higher performance in size fractionation with a high-speed separation. Coupled, on-line UV/visible turbidimetry yields the relative numbers of fractionated cells and sample recovery. Scanning electron microscopy and quasi-elastic light scattering are employed as uncorrelated techniques for size and morphology analysis of the E. coli strains.