Elliptic solution to the Young-Laplace differential equation

The Young-Laplace equation differential form can be solved under the elliptic representation for a fluid-fluid interface in the range 0 相似文献   

Isotachophoresis of allergenic extracts

One aspect of the isotachophoretic determination of protein patterns in biological samples of interest is the characterization of allergens. This group of (glyco) proteins, causing allergic reactions, is used both for diagnosis and in the treatment of allergy. The aim of this investigation was to obtain a maximum amount of information, within one run, on the (glyco)protein composition of a number of allergenic extracts (e.g., from pollen or house dust mites). Commercially available extracts were dialysed prior to analysis to remove disturbing buffer constituents. A high-pH system was chosen in order to obtain a maximum amount of information from the samples (1-2 microliter). The leading electrolyte was 0.01 M C1-, buffered with Tris (pH 8.2), containing 0.2% w/v hydroxyethylcellulose, and the terminating electrolyte was beta-alanine, buffered to pH 10 with Ba(OH)2. The total analysis time was 15-20 min using a PTFE capillary (0.2 mm I.D.). The pre-separation current was 30 microA and the current during detection was 15 microA. UV absorption was measured at 280 nm. For optimal discrimination of the compounds of interest, an ampholyte mixture was used for spacing. The analytical procedure yielded highly reproducible UV patterns. Significant differences between various allergenic extracts were observed. It was concluded that isotachophoresis is a powerful method for the physico-chemical characterization of individual allergenic extracts, e.g., with respect to manufacturing and quality control.     

Detection of Natural Cr(VI) with Computer Screen Photo-assisted Technology

The combined use of a computer screen and a webcam has been demonstrated in several cases to provide a platform for measuring optical properties of liquid and solid samples. Here the method is utilized to measure the absorbance change in an analytical procedure aimed at determining the amount of hexavalent chromium (Cr(VI)) in water. The method calibrated on standard solutions was tested on-field on naturally contaminated spring waters. Results show a sufficient resolution to measure Cr(VI) concentration down to 5 ppb. World Health Organization recommends a maximum concentration of 0.05 mg/l (50 ppb) for chromium (as hexavalent) in drinking waters.     

Data evaluation in high-performance liquid chromatography-diode-array detection-fluorescence detection by information theory

The concepts of information theory were applied to the high-performance liquid chromatography (HPLC) technique, with diode-array (DAD) and/or fluorescence (FLD) detections. The information amount for a complete analysis can be computed as a function of analytical parameters, such as the number of analytes, level of concentration, and standard deviation of determinations. By means of the proposed method, the information content of a qualitative and quantitative analysis accomplished by HPLC-DAD-FLD was estimated, and sensitivity was optimized taking into account a maximum information content, while the detection limit was estimated considering that at this level of concentration the information content approaches zero.     

Four-level orthogonal array design as a chemometric approach to the optimization of polarographic reaction system for phosphorus determination

It is the purpose of the present work to provide information on the four-level orthogonal array design and data analysis for the optimization of analytical procedures. In the theoretical part, the construction and characteristics of the OA(16)(4(5)) matrix is described in detail, followed by the data analysis strategy, in which the significance of the different factors is quantitatively evaluated by an analysis of variance (ANOVA) method including per cent contribution, and the difference among four levels for each factor is determined by Duncan's multiple F test. Furthermore, a third-order polynomial model representing response surface is established to estimate the effects for the factors with significant influences. In the application part, the proposed four-level orthogonal array design and data analysis method were applied to optimize polarographic reaction system for phosphorus determination. By conducting 16 preplanned experiments that span the maximum working range of the system, the best experimental conditions for achieving the largest response can be obtained. The expected value for each experimental trial calculated by the third-order regression equation established is in good agreement with the corresponding experimental value. To confirm the validity of the optimization procedure, additional experiments using the recommended conditions were performed. The results demonstrate that satisfactory results can be acquired. Therefore, the proposed four-level orthogonal array design as a chemometric approach to optimize the polarographic reaction system for phosphorus determination is rather efficient and effective.     

The application of the measurement uncertainty concept to in-process control in pharmaceutical development

 Any analytical data is used to provide information about a sample. The "possible error" of the measurement can be of extreme importance in order to have complete information. The measurement uncertainty concept is a way to achieve quantitative information about this "possible error" using an estimation procedure. On the basis of the analytical result, the chemist makes a decision on the next step of the development process. If the uncertainty is unknown, the information is not complete; therefore this decision might be impossible. The major problem for the in-process control (IPC) procedure is that not only the repeatability but also the intermediate precision (which expresses the variations within laboratories related to different days, different analysts, different equipment, etc.) has to be good enough to make a decision. Unfortunately, the statistical information achieved from one single analytical run only gives information about the repeatability. This paper shows that the estimation of the measurement uncertainty for IPC is a way to solve the problem and gives the necessary information about the quality of the procedure. An example demonstrates that an estimate of uncertainty based on the standard deviations of an analytical method gives a value similar to one based on the standard deviations obtained from a control chart. Therefore, the estimation is both a very useful and also a very cost-effective tool. Though measurement uncertainty cannot replace validation in general, it is a viable alternative to validation for all methods that will never be used routinely. Received: 24 May 1996 Accepted: 10 August 1996     

Development of a multiplexed chemiluminescent immunochemical imaging technique for the simultaneous localization of different proteins in painting micro cross-sections

The identification and localization of organic components in the complex stratigraphy of paintings play a crucial role in studies of painting techniques and authentication, restoration, and conservation of artworks. Much scientific effort has been expended for the development of analytical approaches suitable for the investigation and characterization of organic substances, allowing high sensitivity, specificity, and spatial resolution. Proteins (e.g., ovalbumin, casein, and collagen from different animal sources) are one of the classes of organic substances most widely used as painting materials. The analytical techniques commonly used for their analysis (micro Fourier transform infrared spectroscopy, chromatographic techniques, and proteomic approaches) have limits related to the lack of specificity or to the absence of information concerning the stratigraphic localization of the detected proteins. Immunological techniques are a promising alternative approach for the characterization of proteins in artworks. Thanks to the high specificity of antigen–antibody reactions, these techniques are widely used for the analysis of proteins in bioanalytical and clinical chemistry and recently they have been successfully applied in the field of science for conservation of cultural heritage. The present research aimed to develop an ultrasensitive chemiluminescent immunochemical procedure for the simultaneous localization of ovalbumin and bovine casein (two common proteins found in binding media or varnishes of artistic and archaeological samples) in resin-embedded painting micro cross-sections. The possibility of performing the simultaneous identification of different proteins in painting cross-sections is of particular relevance in the field of cultural heritage because samples are often small and available in a limited number; therefore, the maximum amount of information must be obtained from each of them.     

Quantitative validation of a flow-injection determination of penicillin in pharmaceutical formulations by means of a validation program based on an expert system

The quantitative validation of the results of a flow-injection determination of penicillin in pharmaceutical formulations is described. The validation procedure is done by using VALID, which is a generally applicable validation program based on an expert system program. The automated penicillin assay is based on the enzymatic hydrolysis of the penicillin to the corresponding penicilloic acid, which reacts with iodine generated on-line; the iodine consumption is detected amperometrically. The method is evaluated for applicability in pharmaceutical quality control. The complete validation procedure is described. During the program run, the system evaluates the calibration procedure, the drift of the analytical systemm and the effect of the sample matrix. The reliability of the flow-injection method is estimated by evaluating the maximum total error (MTE), which includes both random error and systematic error. The latter was assessed by comparing of the results of the flow-injection method with the results obtained by titration with mercury(II) as the reference method. The user requirement for the assay was an MTE of 10%. The validation procedure showed that the analytical method complied with the requirements for the major part of the concentration range (0.066–0.25 mM).     

Surfactant-coated single-walled carbon nanotubes as a novel pseudostationary phase in capillary EKC

The analytical potential of the use of surfactant-coated single-walled carbon nanotubes (SC-SWNTs) as pseudostationary phase in CE is described. The pseudostationary phase shows an efficient alternative in enhancing electrochromatographic resolution of compounds which are capable of interacting with a nanotube surface, such as aromatic compounds. In general, the resolution is enhanced by increasing nanotube concentration in the buffer but the maximum amount of SWNTs that can be added to background electrolyte was found limited by compatibility with the UV/visible detection. As an alternative, a low-extension partial filling was used, consisting of the introduction into the capillary of concentrated SC-SWNT, just before the sample, with a plug length similar to the sample one. This has been showed as a reliable procedure in increasing resolution and sensitivity by sweeping phenomena. Finally, the potential of SC-SWNTs to perform chiral separations is discussed.     

Estimation of the limit of detection using information theory measures

Definitions of the limit of detection (LOD) based on the probability of false positive and/or false negative errors have been proposed over the past years. Although such definitions are straightforward and valid for any kind of analytical system, proposed methodologies to estimate the LOD are usually simplified to signals with Gaussian noise. Additionally, there is a general misconception that two systems with the same LOD provide the same amount of information on the source regardless of the prior probability of presenting a blank/analyte sample. Based upon an analogy between an analytical system and a binary communication channel, in this paper we show that the amount of information that can be extracted from an analytical system depends on the probability of presenting the two different possible states. We propose a new definition of LOD utilizing information theory tools that deals with noise of any kind and allows the introduction of prior knowledge easily. Unlike most traditional LOD estimation approaches, the proposed definition is based on the amount of information that the chemical instrumentation system provides on the chemical information source. Our findings indicate that the benchmark of analytical systems based on the ability to provide information about the presence/absence of the analyte (our proposed approach) is a more general and proper framework, while converging to the usual values when dealing with Gaussian noise.     

On a nonelementary progress curve equation and its application in enzyme kinetics

The analytical equation describing progress curves of an enzyme catalyzed reaction acting upon the Michaelis-Menten mechanism has been known for the case in which only the free enzyme incurs a loss of its activity, either spontaneously or as a result of an irreversible inhibitor action. The solution of differential equations which defines the rates of enzyme inactivation and substrate utilization is expressed by a nonelementary function in equation of an implicit type that precludes direct calculation of the extent of reaction at any time. Previously, the implicit equations have been rearranged to the alternative formulas and solved by the Newton-Raphson method, but this procedure may fail when used upon the presented equation. For this reason the other root-finding numerical method was applied, and the enzyme kinetic parameters of such numerically solved implicit equation for the reaction mechanism of irreversibly inhibited acetylcholinesterase were fitted to the experimental data by a nonlinear regression computer program.     

Spectrophotometric determination of gallium in alloys and fly-ash with pyridoxal derivatives of thiocarbohydrazide and carbohydrazide

The symmetric derivatives of pyridoxal with thiocarbohydrazide and carbohydrazide, and the asymmetric derivatives of pyridoxal and salicylaldehyde with the same hydrazides have been synthesized and their analytical potential for spectrophotometric and kinetic fluorimetric determination of metal ions was studied. Gallium(III) and PyMAU(1,3-bis{[4-(2-methyl-3-hydroxy-5-hydroxymethyl)pyridyl]methyleneaminourea at pH = 4.2 form a complex with a single absorption maximum at 425 nm, which can be extracted into cyclohexanone in the presence of a controlled amount of sodium perchlorate. The extract has maximum absorbance at 435 nm. Both systems can be used for determining gallium. The optimal range of gallium concentration for measurement in a 1-cm cell is 0.5-1.25 gmg/ml for the procedure in homogeneous medium ((425) = 3.76 x 10(4).mole(-1).cm(-1)) and 0.25-1.25 mug/ml for the extraction procedure ((435) = 5.30 x 10(4) 1.mole(-1).cm(-1). The latter procedure has been applied to the determination of gallium in alloys and fly-ash.     

Application of reference materials for quality assessment in neutron activation analysis-use of information theory

It is generally accepted that an analytical procedure can be regarded as an information production system yielding information on the composition of the analyzed sample. Thus, information theory can be useful and the quantities characterizing the information properties of an analytical method may be applied not only as evaluation criteria but also as objective functions in the optimization. The usability of information theory is demonstrated on the example of neutron activation analysis. Both precision and bias of NAA results are taken into account together with the possible use of reference materials for quality assessment. The influence of the above-mentioned parameters on information properties such as information gain and profitability of NAA results is discussed in detail. It has been proved that information theory is especially useful in choosing suitable reference materials for the quality assessment of routine analytical procedures not only with respect to matrix and analyte concentration in the sample but also to concentrations and uncertainties of certified values in the CRM used. In the extreme trace analysis, CRMs with relatively large uncertainties and very low certified concentrations can still yield rather high information gain of results.     

Determination of effective fixed-charge density in membranes

The fixed-charge density, X, of cation exchange membranes was determined by three different methods: (a) an analytical method, where a membrane in H⁺ form was equilibrated with KCl solution and the amount of exchanged ions determined, (b) the same procedure, but with electric current flow through the membrane, and (c) by measuring an electroosmotic flow through the membrane and calculating X. While methods (a) and (b) yielded essentially the same values, (c) always gave a substantially lower estimate of X. From irreversible thermodynamics, a maximum possible value of X can be calculated, which for four of five membranes tested is lower than the analytically determined charge density. The electroosmotically measured data were always within this limit.     

Estimation of uncertainties in clinical analysis

 Owing to the importance of clinical analysis for human health, it is necessary to have reliable analytical information. Considering that the reliability of analytical information is a complex function of uncertainties of the sample, method, instrumentation, and data processing, it should be observed that the maximum reliability of analytical information is obtained by minimization of uncertainty values. Applying this concept to clinical analysis, the role of spectrometric and electrometric methods is highlighted.     

Analytical Methods for Determination of Non-Nutritive Sweeteners in Foodstuffs

Sweeteners have been used in food for centuries to increase both taste and appearance. However, the consumption of sweeteners, mainly sugars, has an adverse effect on human health when consumed in excessive doses for a certain period, including alteration in gut microbiota, obesity, and diabetes. Therefore, the application of non-nutritive sweeteners in foodstuffs has risen dramatically in the last decade to substitute sugars. These sweeteners are commonly recognized as high-intensity sweeteners because, in a lower amount, they could achieve the same sweetness of sugar. Regulatory authorities and supervisory agencies around the globe have established the maximum amount of these high-intensity sweeteners used in food products. While the regulation is getting tighter on the market to ensure food safety, reliable analytical methods are required to assist the surveillance in monitoring the use of high-intensity sweeteners. Hence, it is also necessary to comprehend the most appropriate method for rapid and effective analyses applied for quality control in food industries, surveillance and monitoring on the market, etc. Apart from various analytical methods discussed here, extraction techniques, as an essential step of sample preparation, are also highlighted. The proper procedure, efficiency, and the use of solvents are discussed in this review to assist in selecting a suitable extraction method for a food matrix. Single- and multianalyte analyses of sweeteners are also described, employing various regular techniques, such as HPLC, and advanced techniques. Furthermore, to support on-site surveillance of sweeteners’ usage in food products on the market, non-destructive analytical methods that provide practical, fast, and relatively low-cost analysis are widely implemented.     

Multielement x-ray fluorescence analysis of ores and products of their processing using the standard background method with a modified universal equation

A new algorithm is proposed for x-ray fluorescence analysis by the standard background method using a modified universal equation common for all analytes. In the new version of the universal equation, complicating factors can be accounted for by introducing additional correcting members into the analytical parameter. The developed procedure allows the analyst to give up numerous constraint equations, simplify the calibration of spectrometers, and improve the rapidity of the analysis of multielement ores and products of their processing without a drop in the accuracy of the results.     

Upper and lower bounds for a serial dilution test

A Poisson-binomial model estimates the concentration of a target microbe from a serial dilution test. The maximum likelihood procedure gives an equation whose solution equals the estimate of the concentration. This paper gives bounds for the solution to this equation that require only minimal calculations.     

Solving the continuum problem of collision-induced dissociation and recombination

The stationary Schrödinger equation with continuum boundary conditions is solved numerically. Quantum probabilities of collision-induced dissociation/recombination for models with two degrees of freedom are calculated using an integral-equation matching procedure together with analytical wavefunctions or finite element solutions alternatively. Model results for He+Ne₂ → He+2Ne are reported.