A new flow field design for polymer electrolyte-based fuel cells

We present a new flow field design, termed convection-enhanced serpentine flow field (CESFF), for polymer electrolyte-based fuel cells, which was obtained by re-patterning conventional single serpentine flow fields. We show theoretically that the CESFF induces larger pressure differences between adjacent flow channels over the entire electrode surface than does the conventional flow field, thereby enhancing in-plane forced flow through the electrode porous layer. This characteristic increases mass transport rates of reactants and products to and from the catalyst layer and reduces the amount of liquid water that is entrapped in the porous electrode, thereby minimizing electrode flooding over the entire electrode surface. We applied this new flow field to a single direct methanol fuel cell and demonstrated experimentally that the new flow field resulted in substantial improvements in both cell performance and operating stability as opposed to the conventional serpentine flow field design.     

A new microdialysis unit for flow injection analysis

Summary A new dialysis unit optimized for FIA is described. It contains both a dialysis cell and a manifold for reagent addition. Both parts are included in the same module. For test purposes, a colorimetric determination of chloride — both with and without dialysis — has been carried out. For the conditions given in the experimental setup, the dialyzing efficiency was ca. 11 %. The dilution loss factor, i.e., dilution caused by the dialysis cell, was ca. 9. The dispersion coefficient (D) for the manifold — excluding the dispersion caused by dialysis — was calculated to 2.2. The analytical performance expressed as repeatability is around 1.3% r.s.d., and the sample throughput is around 80 – 90 samples/h. Potential application areas cover a wide range of possibilities, e.g., foods and feeds, dairy products, soils and plants, water and waste water analysis and fermentation products.

---

Neue Mikrodialyseeinheit für die Fließinjektionsanalyse

     

A new flow injection titration analysis

Summary A new type of flow injection titration method where a well-stirred mixing chamber is placed in the middle of the injection loop of a 6-way valve has been developed. With this method expensive or unstable reagents can be used for the titration. Moreover, it is potentially available for slow titration reactions. Its fundamental characteristics have been investigated using acid-base titration reaction with phenolphthaleine as the indicator. The sampling rate was 60–120 samples per hour and its reproducibility was also high (3%).

---

Neues Verfahren zur Fließinjektions-Volumetrie

     

A factorial design for optimizing a flow injection analysis system

The use of a factorial design for the response exploration of a flow injection (FI) system is described and illustrated by FI spectrophotometric determination of paraquat. Variable response (absorbance) is explored as a function of the factors flow rate and length of the reaction coil. The present study was found to be useful to detect and estimate any interaction among the factors that may affect the optimal conditions for the maximal response in the optimization of the FI system, which is not possible with a univariate design. In addition, this study showed that factorial experiments enable economy of experimentation and yield results of high precision due to the use of the whole data for calculating the effects.     

A factorial design for optimizing a flow injection analysis system

The use of a factorial design for the response exploration of a flow injection (FI) system is described and illustrated by FI spectrophotometric determination of paraquat. Variable response (absorbance) is explored as a function of the factors flow rate and length of the reaction coil. The present study was found to be useful to detect and estimate any interaction among the factors that may affect the optimal conditions for the maximal response in the optimization of the FI system, which is not possible with a univariate design. In addition, this study showed that factorial experiments enable economy of experimentation and yield results of high precision due to the use of the whole data for calculating the effects.     

A versatile total internal reflection photometric detection cell for flow analysis

A total internal reflection (TIR) flow-through cell that is highly tolerant of schlieren effects, has limited hydrodynamic dispersion and does not trap gas bubbles, and which is suitable for sensitive photometric measurements in flow analysis, is described. Light from an optical fibre is introduced into a short length of quartz capillary through the sidewall at an incident angle of ca. 53°. Under this condition, incident light undergoes total internal reflection from the external air-quartz interface and is propagated by successive reflections from the external walls through the aqueous liquid core of the cell. Detection of the transmitted beam is enabled by intentionally introducing an optical coupling medium at a predetermined distance along the capillary wall, which allows the internally reflected light to be captured by a second optical fibre connected to a charge-couple device detector.This configuration embodies a number of the desirable features of a liquid core waveguide cell (i.e. total internal reflection), a multi-reflection (MR) flow cell (i.e. minimum susceptibility to schlieren effects, low hydrodynamic dispersion and little tendency to trap bubbles), and a conventional Z-cell (wide dynamic range). When employed with a flow injection system, a limit of detection of 2.0 μg PL⁻¹ was achieved for the determination of reactive phosphate using the TIR cell, compared with LOD values of 3.8 μg PL⁻¹ and 4.9 μg PL⁻¹ obtained using the MR and Z-cells with same manifold.The combined advantages of schlieren-tolerance and lack of bubble entrapment of the MR cell with the higher S/N ratio and wider dynamic range of a conventional Z-cell, make the TIR cell eminently useful for photometric measurements of samples with widely differing refractive indices.     

A new sample cell design for studying solid-matrix room-temperature phosphorescence moisture quenching

A new sample chamber was developed that can be used in the measurement of the effects of moisture on the room-temperature solid-matrix phosphorescence of phosphors adsorbed onto filter paper. The sample chamber consists of a sealed quartz cell that contains a special teflon sample holder. Sulfuric acid solutions in the quartz cell determine the percentage relative humidity in the cell and also determine the amount of moisture adsorbed onto the filter paper. The new sample chamber is much easier to use than a flowing nitrogen gas system. Results from both systems are compared with respect to ease of use and the amount of moisture adsorbed onto the filter paper.     

A multi-ion sensor cell and data-acquisition system for flow injection analysis

The flow-injection system described is used for the determination of four ions simultaneously with detection by solid-contact polymer-membrane ion-selective electrodes. The construction of the flow cell and data-acquisition system are discussed. The programming language FORTH facilitates the fast data acquisition required for flow injection analysis. The utility of the system is demonstrated by applying it to the simultaneous determination of potassium, calcium, nitrated and chloride in soil extracts; the results are compared with standard procedures.     

A new design for light-breakable polymer micelles

A new and general design strategy is presented for amphiphilic block copolymers whose micellar aggregates can be dissociated by light. A diblock copolymer composed of hydrophilic poly(ethylene oxide) (PEO) and a hydrophobic polymethacrylate bearing pyrene pendant groups (PPy) was synthesized using ATRP. Upon UV light irradiation of polymer micellar solutions, the photosolvolysis of pyrene moieties results in their detachment from the polymer and converts the hydrophobic PPy block into hydrophilic poly(methacrylic acid). This effect leads to complete dissociation of polymer micelles.     

Two-phase flow in microfluidic-chip design of hydrodynamic filtration for cell particle sorting

As one of the flow-based passive sorting, the hydrodynamic filtration using a microfluidic-chip has shown to effectively separate into different sizes of subpopulations from cell or particle suspensions. Its model framework involving two-phase Newtonian or generalized Newtonian fluid (GNF) was developed, by performing the complete analysis of laminar flow and complicated networks of main and multiple branch channels. To predict rigorously what occurs in flow fields, we estimated pressure drop, velocity profile, and the ratio of the flow fraction at each branch point, in which the analytical model was validated with numerical flow simulations. As a model fluid of the GNF, polysaccharide solution based on Carreau type was examined. The objective parameters aiming practical channel design include the number of the branches and the length of narrow section of each branch for arbitrary conditions. The flow fraction and the number of branches are distinctly affected by the viscosity ratio between feed and side flows. As the side flow becomes more viscous, the flow fraction increases but the number of branches decreases, which enables a compact chip designed with fewer branches being operated under the same throughput. Hence, our rational design analysis indicates the significance of constitutive properties of each stream.     

A new approach to the integrated calibration in flow injection analysis

A new proposal how to perform the analytical procedure according to the integrated calibration method is presented. An original flow injection system has been designed for this purpose. When using only a single standard solution, the measurement information gathered during a single analytical course permits construction of four calibration graphs and calculation of as many as four independent estimations of the analyte concentration in the sample examined. As the calibration method applied integrates the set of standards method and the standard addition method, the analytical estimations may be obtained in both the interpolative and the extrapolative manner and the final result can be effectively verified in terms of accuracy. The system developed was experimentally tested on the example of spectrophotometric determination of chromium. It has been proved to be capable of saving time and reagents as well as providing reliable analytical results. Owing to the instrumental simplicity and analytical efficiency the system is expected to be useful for routine analysis.     

A new cell for electrochemical processes

A simple electrochemical reactor is described that fulfills most of the desired goals normally required. It is easy to construct and scale up. The main feature of the design is an electrode sandwich in which cloth separators are used to provide electrical insulation. They provide an inter-electrode space for the electrolyte and give good mass transfer characteristics. The ohmic drop in the solution is very low and the ratio of active electrode area to electrode volume is high. Operating properties have been determined and show that the cell may be applied to systems that might at first seem unfavourable for an electrochemical process, viz.: multi-phase (especially gas/liquid) mixtures and systems with very low concentrations of electroactive species. These proposals have been tested with some organic synthesis and with waste water purification (Cr(VI) reduction). The cell has been shown to perform well and to be inexpensive - both in construction and in operation.     

A timed solenoid injector for flow analysis

Samples can be reproducibly injected into flow-streams by timed switching of a sample stream with a miniature solenoid valve and timer circuit. The device is simpler to assemble and use than the standard rotary valve and a direct comparison under the same operating conditions shows that the solenoid valve is an adequate replacement for the rotary valve.     

A microfluidic channel flow cell for electrochemical ESR

The design, fabrication, and characterization of microfluidic channel flow devices for in situ simultaneous hydrodynamic electrochemical ESR is reported. The microelectrochemical reactors consist of gold film electrodes situated within rectangular ducts of height 350 microm and widths in the range 500-2000 microm. The small dimensions of the channels result in minimal dielectric loss when centralized within a cylindrical TE011 resonant cavity, leading to a high level of sensitivity. This is demonstrated by using the one-electron oxidation of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) in acetonitrile as a model system, wherein the ESR spectra obtained for the corresponding stable radical cation are of a high signal-to-noise ratio. Signal intensity is measured as a function of flow rate for this system, and the behavior is validated by means of 3-dimensional numerical modeling of the hydrodynamic flow profile.     

Optimisation of cell design for activation analysis of flowing systems

A theoretical relationship between the half-life and activity of a radioisotope produced by neutron activation of a flowing system, the flow rate, and the irradiation, delay and counting volumes is developed. An expression is then obtained for the flow rate producing maximum activity of the radioisotope. Both expressions have been solved using a digital computer for a variety of half-lives, activities and combinations of irradiation, delay, and counting volumes. It has been shown that, for any given system, the activity as a product of the half-life and corresponding flow rate is independent of the half-life.     

A new quality control method for lateral flow assay

We proposed a lateral flow assay (LFA) based on internal quality control microspheres to realize the accurate diagnosis of HbA1c in human body. This method can improve the precision and accuracy of HbA1c detection.     

A new method for thermal analysis

In this study, we developed the technique of Li⁺ ion-attachment mass spectrometry (IAMS), a method that has shown promise in the fields of chemical analysis, plasma diagnostics, chemical process monitoring, and thermal analysis. The experimental setup is such that Li⁺ ions get attached to chemical species (R) by means of intermolecular association reactions to produce (R?+?Li)⁺ adduct ions, which are then transferred to a quadrupole mass spectrometer. Recently, an IAMS system became available commercially in a complete form from the Canon Anelva Corp. IAMS has several notable features. It provides only molecular ions, and it permits direct determination of unstable, intermediary, and/or reactive species. Also, it is highly sensitive because it involves ion-molecule reactions. With regard to its applications for thermal analysis, one of its greatest advantages is that it can be used to directly analyze gaseous compounds because it provides mass spectra only of the molecular ions formed by Li⁺ ion attachment to any chemical species introduced into the spectrometer, including free radicals. Coupled with evolved gas analysis, IAMS works well for the analysis of nonvolatile, untreated, and complex samples because the simplicity of the ion-attachment spectrum permits the analysis of mixtures electron-impact spectra of which are difficult to interpret.     

A new compact interferometer design

The optical layout of a compact interferometer suitable for Fourier transform spectroscopy is presented. The constraints on the practical implementation of this design are discussed. Specifications are given for the collimating optics, the optical finish of the interferometer components, and the allowable mirror tilt.     

Stepwise injection analysis as a new method of flow analysis

Various versions of flow analysis techniques (continuous-flow, flow-injection, and sequential-injection analysis) and their relative advantages and disadvantages are considered. Cyclic (stepwise) injection analysis is proposed, and the general principles of this technique are described.     

A new paradigm for protein design and biological self-assembly

Very few molecules with biological origins contain the element fluorine. Nature's inability to incorporate fluorine into biomolecules is related to the low concentration of free fluoride in sea and surface water. However, judicious introduction of fluorine into proteins, nucleic acids, lipids and carbohydrates has allowed mechanistic scrutiny of enzyme catalysis, control of protein oligomerization in membranes, clustered display of ligands on surfaces of living cells, and in increasing the protease stability of protein and peptide therapeutics.