Simple Analytical Techniques Research Articles

(Invited) Diagnostics of Fuel-Cell Performance Utilizing Simple Graphical Methods Based on Theoretical Limiting Cases

A systematic methodology to determine what is limiting the performance of a fuel cell will be presented. The basis of this methodology is to utilize in-situ cell data combined with simple analytical techniques. The key analytical techniques are based on theoretically-predicted limiting cases for the different types of overpotential that can limit the performance of a polymer-electrolyte fuel cell (PEFC). These limiting cases are compared to PEFC performance data utilizing simple graphical techniques in order to provide semi-quantitative insight into the mechanisms primarily responsible for the cell polarization observed operating under the operating conditions of interest. This diagnostic methodology is ideally suited to investigate changes in the performance of a fuel cell. For example, the use of this methodology to investigate durability losses in PEFCs has been described [1]. However, the same techniques can be used to determine why the performance of one type of cell is different than a cell of a different configuration, or why the performance of a given cell varies with different operating conditions. Examples of each of these types of cell-performance investigations will be used to illustrate the methodology. The diagnostic method recommended here is a systematic, step-by-step method. The first step is to determine what major type(s) of overpotential are responsible for the changes in performance, namely: kinetic, ohmic, or mass transport. Polarization-change curves, such as those depicted in Figure 1, are a simple and useful tool to assist in apportioning performance changes to the different types of overpotential. The limiting cases depicted in Figure 1 were constructed with a relatively simple model of cell polarization [1]. These simple limiting cases, as well as some actual polarization-change curves examples, will be presented. Once the major types of overpotential have been identified, additional cell diagnostics can be selected to establish the sources (i.e., cell components and/or locations) of these changes. In-cell diagnostics for each of the major types of polarization are also recommended. For example, to determine whether mass-transport resistance is increasing within or external to the catalyst layer (or catalyst agglomerate) one can utilize an oxygen-gain analysis, which is based on a relatively simple model of the cathode potential and the two limiting cases predicted by this model [2]. To determine whether mass-transport losses are primarily due to oxygen transport and/or proton transport (i.e., ohmic losses in the catalyst layer), one can utilize an oxygen-dependence analysis, which is also based on limiting cases predicted by a simple model of the cathode [3]. The examples used to illustrate these diagnostic techniques will be on state-of-the-art PEFCs, so that the actual performance limitations being investigated should also be of interest to PEFC research community, such as mass-transport losses in PEFCs with ultra-low catalyst loadings. Acknowledgements Thanks to the organizers of this Symposia for the invitation to present. The author would also like to thank his many fuel-cell collaborators at United Technologies Corporation (both past and present). Funding from U.S. Department of Energy, EERE’s Fuel Cell Technologies Office under contract numbers DE-AC02-05CH11231 and DE-AC02-06CH11357 has enabled much of the recent work at UTRC on PEFCs that will be used as examples here, and is also gratefully acknowledged.

An optimal design of a mono-stable vertical diamagnetic levitation based electromagnetic vibration energy harvester

A detailed analysis of a mono-stable vertical diamagnetic levitation (VDL) system for optimal vibration energy harvesting is presented. Initial studies showed that simple analytical techniques such as the dipole model and the image method provide useful guideline for understanding the potential of a diamagnetic levitation system, however, it is discussed here that the more accurate semi-analytical techniques such as the thin coil model and the discrete volume method are needed for quantitative optimization and design of the VDL system. With the semi-analytical techniques, the influence of the cylindrical geometry of the floating magnet, the lifting magnet and the diamagnetic plate are parametrically studied to assess their effects on the levitation gap, size of the system and the natural frequency.For efficient vibration energy harvesting using the VDL system, ways to mitigate eddy current damping and a coil geometry for transduction are critically discussed. With the optimized parameters, an experimental system is realized which showed a hardening type nonlinearity. The results show an overall efficiency of 1.54 percent, a root mean square (rms) power output of 1.72µW when excited at a peak acceleration of 0.081m/s2 and at a frequency of 2.1Hz.

Effect of temperature on the analysis of asphaltenes by the on-column filtration/redissolution method

The study of the effect of temperature on the analysis of asphaltenes by the on-column filtration/redissolution method is presented. The goal of this work is the prediction and early detection of asphaltene/solid precipitation at reservoir and refining conditions using simple, fast and reliable analytical techniques. A description of the new experimental methodology is introduced followed by the results of the analysis of n-heptane asphaltenes and virgin, vacuum residue (VR), visbroken and hydroprocessed petroleum samples in the temperature range 35–195°C. Mass balances were effectively carried out and the presence of adsorbed species on the column surface was found. Consistent with gravimetrically separated asphaltenes, the new method showed that asphaltene contents are reduced as the temperature is raised whereas the maltene contents increased. Similar behavior was found for separated asphaltenes and whole virgin, VR or whole hydroprocessed samples. In general, it was observed that the amount of adsorbed species seems to increase with the temperature.

Lipid and lipoarabinomannan isolation and characterization.

Mycobacteria are microorganisms that contain a very high content of structurally diverse lipids, some of them being biologically active substances. As such the lipid composition is commonly used to characterize mycobacterial strains at the species and type-species level. This chapter describes the methods that allow the purification of the most commonly isolated biologically active lipids and those used for analyzing extractable lipids and their constituents, cell wall-linked mycolic acids and lipoarabinomannan (LAM). The latter involve simple chromatographic and analytical techniques, such as thin-layer chromatography and gas chromatography coupled to mass spectrometry.

First derivative potentiometric and spectrophotometric determinations of cimetidine in tablets

Cimetidine is an imidazole derivative, which acts as H2-receptor antagonist to inhibit gastric acid secretion and is thereby useful in the treatment of ulcers and other hyperacidity stomach disorders. This study sets out to provide simple, inexpensive and sensitive analytical techniques for the assay of cimetidine in tablet dosage forms using first derivative potentiometric and UV-spectrophotometric techniques, with a view to providing simple, sensitive and cost-effective analytical methods. Ten brands of cimetidine tablets were purchased from pharmacies in Yenagoa and Port Harcourt, Niger Delta region of Nigeria. The samples were assayed by Potentiometric and UV spectrophotometric methods after a Thin Layer Chromatographic (TLC) fingerprint. The potentiometric assay results of the samples ranged from 92-100% of stated amount for 70% of the samples. The coefficient of variation for In-between run, Intra-day run and accuracy of the UV spectrophotometric method was within 3%. The percentage purity of cimetidine from UV determination at 260 nm ranged from 86 - 97%, showing that 50% of the samples conformed to the stated standard – ie: contain 95- 105% of stated amount. The TLC fingerprints of the samples were similar in many respects, including R f values which ranged from 0.8 to 0.9 compared to the reference sample with R f value of 0.9. The results suggest that either of the two methods can be fine-tuned for assay of cimetidine in tablet formulations. Keywords: Potentiometry, ultraviolet (UV) spectrophotometry, analytical methods, cimetidine, Tablet Formulations, volumetric standard (VS)

Petrologic Evolution of a Nipigon Diabase Sill, Ontario, Canada: Insights From Compositional and Textural Profiles

Petrographic and geochemical profiles collected through a ~250-m-thick Nipigon diabase sill near Black Sturgeon Lake, Ontario, constrain the complex emplacement and differentiation processes that controlled the magmatic evolution of these rocks: several nested reinjections of phenocryst-bearing magma, compactiondriven redistribution of mildly evolved interstitial liquids in the central portion of the sill, and segregation of highly-evolved interstitial liquids into micropegmatitic veins near the upper contact. These processes impact not only the silicate mineralogy of the rocks, but also distribution of sulfide phases. Both petrographic and geochemical data demonstrate that the sill was gradually inflated via several discrete injections of olivine-bearing magma. Plagioclase crystal size trends exhibit several reversals that are correlated with increases in olivine abundance and bulk-rock MgO content. These textural and compositional reversals are attributed to reinjections of olivine-bearing magma into partially solidified magma from earlier injections. Mixing between evolved resident magma and reinjections of less-evolved magma is commonly proposed as a mechanism for triggering sulfide mineralization. In this sill, which contains no significant mineralization, localized minor enrichments and depletions in copper content are associated with the margins of a well-constrained reinjection horizon. Chemical differentiation of the magma was controlled by three distinct processes: flow differentiation, crystal-mush compaction, and solidification front instability. Although the mineralogy of the sill is dominated by plagioclase and clinopyroxene, major-oxide compositional variations are largely controlled by the mechanical concentration of olivine via flow differentiation or phenocryst redistribution within the individual reinjection pulses. This redistribution of phenocryst phases is the primary factor controlling the major-element composition of the rocks in most of the sill. In the central portion of the sill, the abundances of incompatible trace elements are influenced by the compaction of partially crystalline mush and the expulsion of incompatible-rich interstitial liquid. This is recognized by a negative correlation between the alignment of plagioclase crystals and concentrations of incompatible trace elements such as Zr. Finally, there is a ~2.5-m-thick silicic segregation approximately 32 m below the upper contact, whose composition is consistent with residual liquid after ~65 to 85% fractional crystallization of magma with a composition equivalent to that of the marginal rocks. Similar veins and patches are common throughout the upper 50 m of the sill, indicating that this segregation process was common and widespread during the cooling and crystallization of the sill. The complexity of intrusion and differentiation in this sill, despite its generally unremarkable texture and composition, suggests that many diabase sills may have experienced a range of processes that have previously been recognized to impact the petrologic evolution of larger igneous systems, and that these processes can be identified in minor intrusions such as sills and dikes using simple and robust analytical techniques.

An application of the PEER performance based earthquake engineering framework to structures in fire

The Pacific Earthquake Engineering Research (PEER) Center’s Performance Based Earthquake Engineering (PBEE) framework is well documented. The framework is a linear methodology which is based upon obtaining in turn output from each of the following analyses: hazard analysis; structural analysis; loss analysis, and finally decision making based on variables of interest, such as downtime or cost to repair. The strength of the framework is in its linearity, its clear flexibility and in the consideration of uncertainty at every stage of the analysis. The framework has potential applications to other forms of extreme loading; however in order for this to be achieved the ‘mapping’ of the framework to the analysis of structures for other loading situations must be successful.This paper illustrates one such ‘mapping’ of the framework for Performance Based Fire Engineering (PBFE) of structures. Using a combination of simple analytical techniques and codified methods as well as random sampling techniques to develop a range of response records, the PEER framework is followed to illustrate its application to structural fire engineering. The end result is a successful application of the earthquake framework to fire which highlights both the assumptions which are inherent in the performance based design framework as well as subjects of future research which will allow more confidence in the design of structures for fire using performance based techniques.This article describes the PEER framework applied to structural earthquake design then follows the framework from start to completion applying suitable alternative tools to perform each stage of the analysis for structures in fire.

Spectrophotometric and bioassay methods for the estimation of erythromycin formulation

Erythromycin is a naturally occurring chemotherapeutic agent used in the treatment of aerobic gram positive cocci, bacilli and a few gram negative organisms. In view of its resurgent use due to resistance to anti-bacterial chemotherapy, the study sets out to provide simple, sensitive and cost-effective analytical and bioassay techniques involving UV-spectrophotometric and Microbiological methods. Method validation was by means of a precision and accuracy assays. Ten brands of erythromycin formulation comprising, seven tablets and three suspension dosage forms were assayed by UV spectrophotometric at the λmax of 285nm and bioassay methods. Thin Layer Chromatographic (TLC) method was used to establish the identity of the active ingredient in the formulations. The spectrophotometric results, expressed as a percentage of stated amounts of erythromycin were 79 - 120%w/w, which shows that 70% of the test samples conformed to the official stated standard. The bioassay determination gave MICs ranging from 0.5-2µg/ml for all the samples, 0.5μg/ml and 1.0μg/ml for reference erythromycin against S. aureus and B. subtilis , respectively. Thus, 80% of the samples met the bioassay requirement. TLC fingerprint gave Rf values ranging from 0.71 - 0.79 for 80% of the samples while the remaining 20% gave no change in colour, elution nor increase in size of the principal spot. Hence, no single method could be adequate in the determination of the quality of pharmaceutical formulations.

Characterisation and authentication of A. senegal and A. seyal exudates by infrared spectroscopy and chemometrics

The authentication of Acacia gums samples requires usually the use of sophisticated and time consuming analytical techniques. There is a need for fast and simple analytical techniques for the objective of a quality control methodology. Commercial Acacia senegal and Acacia seyal gums present characteristic MIR spectra. Principal Component Analysis of the infrared spectra of gum exudates of trees allow to distinguish Acacia gums from another gum exudates (Combretum, Ghatti, Karaya, Tragacanth). Moreover, gums of A. senegal and A. seyal separate them and from other Acacia species (Acacia dealbata, Acacia karoo, Acacia nilotica, Acacia sieberiana). Chemometric treatments of A. senegal and A. seyal MIR spectra were assessed for the quantification of moisture content in Acacia gums, for the classification into the two species and for the adulteration detection and quantification. Results were quite satisfactory, the moisture content was estimated at 3.1%, adulteration was detected at 3.4% and quantified at 5.6%. The discrimination of the two species is done without any ambiguity.

Analysis of Argan Oil Adulteration Using Infrared Spectroscopy

ABSTRACT The determination of argan oil adulteration by other vegetable oils is a real analytical challenge. The authentication of argan oil needs fast and simple analytical techniques for quality control and testing. This study focuses on the detection and quantification of argan oil adulteration with different edible oils, using midinfrared spectroscopy with chemometrics. Chemometric treatment of MIR spectra has been assessed for the classification and quantification of argan oil adulteration with sunflower or soybean oils. The potential of MID spectroscopy combined with partial least squares regression (PLS) as a rapid analytical technique for the quantitative determination of adulterants in argan oil has been demonstrated. A PLS model has been established to predict the concentration of soybean and sunflower oil as adulterants in the calibration range between 0% and 30% (w/w) in argan oil with good prediction performances in the external validation.

Simple and cost-effective spectrophotometric and titrimetric methods for the determination of ciprofloxacin in tablets

Ciprofloxacin is a synthetic chemotherapeutic agent used in the treatment of infections caused by gram negative and gram positive bacteria. Due to its versatility in anti-bacterial chemotherapy, this study sets out toprovide simple, in-expensive and sensitive analytical techniques involving UV-spectrophotometric and titrimetric methods. Method validation was by means of a precision assay. The methods were applied to thedetermination of ciprofloxacin hydrochloride in tablets available within the Nigerian drug distribution system. Ten different brands of ciprofloxacin tablets were analysed for ciprofloxacin by UV spectrophotometry at theëmax of 271.5 nm and redox titration using KMnO4 in alkaline medium. The spectrophotometric results, expressed as a percentage of stated amounts of ciprofloxacin were 95.5 - 103.5%w/w, while the titrimetric results were 95.0 - 100.3%w/w. Some 70% of the results from the two methods were in line with the high performance liquid chromatographic method specified by BP 2008. The results show that both the spectrophotometric and titrimetric methods described are suitable for the assay of ciprofloxacin in tablets.

Shrinking-core modeling of binary chromatographic breakthrough

Most chromatographic processes involve separation of two or more species, so development of a simple, accurate multicomponent chromatographic model can be valuable for improving process efficiency and yield. We consider the case of breakthrough chromatography, which has been considered in great depth for single-component modeling but to a much more limited degree for multicomponent breakthrough. We use the shrinking core model, which provides a reasonable approximation of particle uptake for proteins under strong binding conditions. Analytical column solutions for single-component systems are extended here to predict binary breakthrough chromatographic behavior for conditions under which the external transport resistance is negligible. Analytical results for the location and profile of displacement effects and expected breakthrough curves are derived for limiting cases. More generally, straightforward numerical results have also been obtained through simultaneous solution of a set of simple ordinary differential equations. Exploration of the model parameter space yields results consistent with theoretical expectations. Additionally, both analytical and numerical predictions compare favorably with experimental column breakthrough data for lysozyme–cytochrome c mixtures on the strong cation exchanger SP Sepharose FF. Especially significant is the ability of the model to predict experimentally observed displacement profiles of the more weakly adsorbed species (in this case cytochrome c). The ability to model displacement behavior using simple analytical and numerical techniques is a significant improvement over current methods.

Understanding First, Simulation Later

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 132781, ’Understanding First, Simulation Later: Using Basic and Modern Reservoir- Engineering Techniques To Understand Reservoir Dynamics: A Proven Case,’ by Hector Gomez Alonso, SPE, Sarawak Shell Berhad, originally prepared for the 2010 SPE Annual Technical Conference and Exhibition, Florence, Italy, 19-22 September. The paper has not been peer reviewed. The full-length paper describes a mature field in which water production was seen very early in production life and rapidly increased to the current level of 80% water cut. At well level, a similar behavior has been noticed: high initial oil rates with subsequent strong decline once water breakthrough occurs. This type of behavior has been observed in most of the wells completed among the different reservoirs that make up the field. Long-term production data and modern decline analysis strongly indicated the presence of two systems in the reservoir. Introduction The full-length paper shows how important it is to have a strong understanding of reservoir dynamics before using 3D reservoir-simulation models and, especially in this case, how the use of simple and modern analytical techniques such as Chan plots, transient tests, and conventional and modern decline analysis can provide the reservoir engineer with sufficient background to take the next step confidently. The paper also describes how pseudosteady-state calculations provided information regarding the characteristics of the second system, which helped to optimize the original petrophysical interpretation in the static model. This represents a simple approach to consider how detailed a geological model need to be to reproduce production behavior. Usually, in mature fields, there is a considerable amount of information available regarding production, pressures, fluid samples, and transient tests, which sometimes is not analyzed properly because there is not sufficient time or the data are not easy to find. Reservoir engineers sometimes have the tendency to jump directly into dynamic simulation to understand the dynamics in the reservoir and generate predictions. The objective of following the methodology described, before engaging in the use of reservoir simulation, is to try to understand what really is going on at the subsurface level. If this is achieved, the reservoir engineer always will be ahead of the simulation model and not the other way around. Simulation models should be treated as tools in which equations are solved, by using input data (e.g., rates, pressures, pressure/volume/temperature, and relative permeability).

The Hercules Satellite: A Stellar Stream in the Milky Way Halo?

We investigate the possibility that Hercules, a recently discovered Milky Way (MW) satellite, is a stellar stream in the process of formation. This hypothesis is motivated by Hercules' highly elongated shape as well as the measurement of a tentative radial velocity gradient along its body. The application of simple analytical techniques on radial velocity data of its member stars provides tight constraints on the tangential velocity of the system (v_t = -16^{+6}_{-22} km/s, relative to the Galactic Standard of Rest). Combining this with its large receding velocity (145 km/s) and distance (138 kpc) yields an orbit that would have taken Hercules to within 6^{+9}_{-2} kpc of the Galactic centre approximately 0.6 Gyr ago. This very small perigalacticon can naturally explain the violent tidal destruction of the dwarf galaxy in the MW's gravitational potential, inducing its transformation into a stellar stream.

Analysis and control of high sideslip manoeuvres

This paper presents simple analytical techniques that are used to understand and control high sideslip drift manoeuvres of road vehicles. These are manoeuvres in which a skilled driver stabilises a vehicle beyond its limits of handling, an operating regime responsible for major safety concerns in everyday driving. An analysis of the equilibria of a bicycle model with nonlinear tyres reveals the existence of unstable ‘drift equilibria’ corresponding to cornering at high sideslip angle in a countersteer configuration. Equipped with this information, linearisation about a desired drift equilibrium is used to design a controller that stabilises the vehicle at the equilibrium. The controller is subsequently implemented on a steer- and drive-by-wire testbed and successfully used to achieve autonomous drifts.

THE HERCULES SATELLITE: A STELLAR STREAM IN THE MILKY WAY HALO?

We investigate the possibility that the recently discovered Hercules Milky Way satellite is in fact a stellar stream in formation, thereby explaining its very elongated shape with an axis ratio of 3 to 1. Under the assumption that Hercules is a stellar stream and that its stars are flowing along the orbit of its progenitor, we find an orbit that would have recently brought the system close enough to the Milky Way to induce its disruption and transformation from a bound dwarf galaxy into a stellar stream. The application of simple analytical techniques to the tentative radial velocity gradient observed in the satellite provides tight constraints on the tangential velocity of the system (v_t = -16^{+6}_{-22} km/s in the Galactic Standard of Rest). Combined with its large receding velocity, the determined tangential velocity yields an orbit with a small pericentric distance (R_peri = 6^{+9}_{-2} kpc). Tidal disruption is therefore a valid scenario for explaining the extreme shape of Hercules. The increase in the mean flattening of dwarf galaxies as one considers fainter systems could therefore be the impact of a few of these satellites not being bound stellar systems dominated by dark matter but, in fact, stellar streams in formation, shedding their stars in the Milky Way's stellar halo.

Development of colorimetric analytical methods to monitor quaternary amine grafted surfaces

AbstractQuick and simple colorimetric analytical techniques were developed to monitor functionalization of surfaces with quaternary amine bearing polymers as complementary qualitative tests to the traditionally used antimicrobial test protocols. First, an established antimicrobial quaternary ammonium salt (QAS) was chosen as a probe compound and an acrylol functional group was introduced (acrylol‐QAS) to facilitate its polymerization with acrylic monomers. Surface graft polymerization was carried out with methyl methacrylate (MMA) and acrylol‐QAS on cotton fabric surface. The success of graft polymerization, durability after repetitive aqueous extraction, and the effect of crosslinking agents on the durability and extent of polymerization were tested with a fluorescein spot and a bromophenol solution test. The results of these colorimetric analytical methods were in perfect agreement with those of antimicrobial tests, XPS, and SEM analysis. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Characterization of different humic materials by various analytical techniques

In a previous paper, we studied the characterization of the three humic materials, humic acid, fulvic acid and humin, by simple analytical techniques such as elemental analysis and potentiometric titration. In this work, the same humic fractions were investigated by the developed analytical methods CP/MAS 13C NMR, IR and visible spectroscopy’s; to evaluate the harmony of the different analytical methods used for characterization of humic materials and to recognize and evaluate the properties of humic acid, fulvic acid and humin separated from the same source. The results of these developed analytical methods were compared with that of simple analytical techniques. It was found that the low cost simple analytical techniques are suitable for description of humic materials, where the results are in fine agreement with each other. The E3/E5 ratio was found to designate a more or less similar indication like E4/E6 ratio.

Comparing the Old and New: Traditional Building Materials and the Uch Monument Complex, Pakistan

The supposition that modern traditionally produced building materials are inherently similar to original building fabric is common in Pakistan. Laboratory analysis on historic and modern samples of fired brick, mud brick, and mud mortars was undertaken for the first time in the region to investigate similarities in basic physical properties and composition of the materials. Simple analytical techniques were used to determine porosity, density, particle size distribution, plastic limit and other properties, as well as chemical composition of the samples. Further analytical methods were used to confirm the results of simpler analyses and further characterize materials. Results indicate that modern locally produced materials were in many ways comparable to their historic counterparts and may be used as intervention materials within the buildings of the Uch Monument Complex. This information will inform the choice and manufacture of proposed intervention materials, while providing preliminary quantitative evidence for continuing traditions.

Determination of organic compounds from wood combustion aerosol nanoparticles by different gas chromatographic systems and by aerosol mass spectrometry

Organic compounds in atmospheric nanoparticles have an effect on human health and the climate. The determination of these particles is challenged by the difficulty of sampling, the complexity of sample composition, and the trace-level concentrations of the compounds. Meeting the challenge requires the development of sophisticated sampling systems for size-resolved particles and the optimization of sensitive, accurate and simple analytical techniques and methods. A new sampling system is proposed where particles are charged with a bipolar charger and size-segregated with a differential mobility analyzer. This system was successfully used to sample particles from wood pyrolysis with particle sizes 30-100nm. Particles were analyzed by four techniques: comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry, gas chromatography-time-of-flight mass spectrometry, gas chromatography-quadrupole mass spectrometry, and aerosol mass spectrometry (aerosol MS). In the chromatographic techniques, particles were collected on a filter and analyzed off-line after sample preparation, whereas in the aerosol MS, particle analysis was performed directly from the particle source. Target compounds of the samples were polyaromatic hydrocarbons and n-alkanes. The analytical techniques were compared and their advantages and disadvantages were evaluated. The sampling system operated well and target compounds were identified in low concentrations.