Quantitative Determination of Ambroxol Hydrochloride in Syrups by RP-HPLC and UV Spectroscopy

RP-HPLC and UV Spectroscopy methods for the quantitation of ambroxol hydrochloride in syrups have been developed. Both methods were precise and accurate. A number of inactive ingredients present in the synthetic syrup did not interfere with the assay procedures. Although the methods had also good recovery for commercial syrups, but it was difficult to determine which method was more accurate than the other.     

Development and Validation of a Rapid HPLC Method for the Determination of Ketotifen in Pharmaceuticals

ABSTRACT

In the present study, a simple, sensitive, rapid, and stability-indicating high performance liquid chromatographic (HPLC) method with ultraviolet detection for the analysis of ketotifen was developed and validated. The method was applied to the determination of ketotifen in pharmaceutical formulations (tablets and syrups). The HPLC method utilized isocratic elution technique with a reversed phase C8 column, detection at 297 nm and a mixture of methanol, triethylamine phosphate buffer (pH 2.8; 0.04 M), and tetrahydrofuran (43: 55: 2, v/v/v) as mobile phase at a flow rate of 1.2 mL/min. Total analysis time was about 7 min with typical retention time of ketotifen of about 5 min. The method was validated for selectivity, linearity, accuracy, and precision following International Conference of Harmonization, 1996 (ICH) recommendations. Due to its simplicity and accuracy, the method can be used for routine quality control analysis.     

Analytical and Numerical Approximations in Fresnel Diffraction

Abstract

Procedures for the fast and accurate numerical computation of Fresnel diffraction integrals are developed on the basis of geometrical properties of the Cornu spiral. The methods proposed allow the highly oscillatory integrals in Fresnel diffraction to be approximated by means of three simpler integrals and permit the calculation of these final integrals using analytical formulae.     

Residual strength of reinforced concrete columns exposed to fire

Abstract

Several methods were employed to evaluate the residual strength of reinforced concrete columns exposed to different durations of fire. These methods included the analytical method, ultrasonic tests, hammer tests and load tests. Fifty columns were involved in the tests. Calculated temperatures and residual strengths of the test columns were compared with those measured. Comparisons were also made between results from load tests and those from nondestructive tests. The results showed that using analytical procedures is acceptable while the nondestructive test methods are accurate only for shorter durations of fire.     

The Stability of Oral Liquids

Abstract

Many types of formulations both aqueous and non-aqueous are included among those which can be classified as oral liquids. Included in this group are syrups, suspensions, emulsions, colloids, mouthwashes, elixirs, and soft gelatin capsules. It will not be possible to cover in detail all the different formulations or factors which will effect their stability; however, those discussed should have some applicability to all systems. It is safe to say that, as a class of formulations, oral liquids are generally more complex in their composition than parenterals and, therefore, more interactions can occur which might affect the stability of the product. Not only is it necessary to consider the solution stability of the drug substance, but also the effects upon stability caused by such things as suspending agents, colorants, flavors and sweetening agents need to be addressed.     

Solution of the Fourth-moment Equation by an Adaptive Grid Method

Abstract

The parabolic fourth moment equation for a plane wave is integrated numerically using an adaptive grid algorithm. Results are compared with those from an accurate, but far less efficient, operator splitting method, and agree very closely. The adaptive approach has several advantages over current fixed grid methods. The primary one is that significant reductions in computer memory usage can be obtained without a concomitant increase in run time. It is also ideally suited for accurate integration of the fourth-moment equation for an extremely large range of values of both the scattering parameter, Γ, and the wave propagation distance.     

Statistical Parameters for Characterizing the Indicating Surface of Natural Reflectance in Absorbing Uniaxial Media

Abstract

The indicating surface of natural reflectance for absorbing uniaxial media is studied in this paper. Expressions for the maximum, minimum, mode and median of the distributions of natural reflectances have been obtained. In order to obtain accurate values of the mean natural reflectance and its standard deviation, it is necessary to resort to numerical methods. When, in the expression of the mean natural reflectance corresponding to transparent media, the real refractive index is replaced by the complex one, these expressions are also valid for the particular case of weakly absorbing media. To obtain accurate values for the standard deviation, it is also necessary to resort to numerical methods. The values calculated for several theoretical cases and for five minerals—in air and in oil—are compared with those obtained using a simulation method, and both sets of results are in good agreement.     

Optimally Generalized Regularization Methods for Solving Linear Inverse Problems

In order to solve ill-posed linear inverse problems, we modify the Tikhonov regularization method by proposing three different preconditioners, such that the resultant linear systems are equivalent to the original one, without dropping out the regularized term on the right-hand side. As a consequence, the new regularization methods can retain both the regularization effect and the accuracy of solution. The preconditioned coefficient matrix is arranged to be equilibrated or diagonally dominated to derive the optimal scales in the introduced preconditioning matrix. Then we apply the iterative scheme to find the solution of ill-posed linear inverse problem. Two theorems are proved that the iterative sequences are monotonically convergent to the true solution. The presently proposed optimally generalized regularization methods are able to overcome the ill-posedness of linear inverse problems, and provide rather accurate numerical solution.     

Statistical Comparison of Two Methods of Dissolution of Sustained-Release Theophylline Tablets

Abstract

A comparative study of two methods of dissolution (Simoons Apparatus and USP XXII Apparatus II) has been accomplished using sustained-release 50 mg anhydrous theophylline tablets. Sovic® 374 MB, Eudragit® RL PM, Aquacoat®, Methocel® K-15M, and Cutina® HR were some of the excipients used to elaborate inert, hydrophilic, and lipidic matrices. Theophylline release was prolonged in all cases, except when Aquacoat was used as matrix constituent. Simoons device was found to be more accurate for inert matrix tablets, whereas USP apparatus was advantageous for hydrophilic and lipidic matrix. ANOVA showed significant differences among all the factors analyzed. The drug release kinetics was adjusted better to Higuchi's kinetic model than to the Noyes-whitney or Weibull models, from 10% to 70% release.     

Numerical techniques for high-throughput reflectance interference biosensing

Abstract

We have developed a robust and rapid computational method for processing the raw spectral data collected from thin film optical interference biosensors. We have applied this method to Interference Reflectance Imaging Sensor (IRIS) measurements and observed a 10,000 fold improvement in processing time, unlocking a variety of clinical and scientific applications. Interference biosensors have advantages over similar technologies in certain applications, for example highly multiplexed measurements of molecular kinetics. However, processing raw IRIS data into useful measurements has been prohibitively time consuming for high-throughput studies. Here we describe the implementation of a lookup table (LUT) technique that provides accurate results in far less time than naive methods. We also discuss an additional benefit that the LUT method can be used with a wider range of interference layer thickness and experimental configurations that are incompatible with methods that require fitting the spectral response.     

In vitro–in vivo correlations: general concepts,methodologies and regulatory applications

Abstract

The major objective of in vitro–in vivo correlations is to be able to use in vitro data to predict in vivo performance serving as a surrogate for an in vivo bioavailability test and to support biowaivers. Therefore, the aims of this review are: (i) to clarify the factors involved during bio-predictive dissolution method development; and (ii) the elements that may affect the mathematical analysis in order to exploit all information available. This article covers the basic aspects of dissolution media and apparatus used in the development of in vivo predictive dissolution methods, including the latest proposals in this field as well as the summary of the mathematical methods for establishing the in vitro–in vivo relationship and their scope and limitations. The incorporation of physiological relevant factors in the in vitro dissolution method is essential to get accurate in vivo predictions. Standard quality control dissolution methods do not necessarily reflect the in vivo behavior, so they rarely are useful for predicting in vivo performance. The combination of physiological based dissolution methods with physiological-based pharmacokinetics models incorporating gastrointestinal variables will lead to robust tools for drug and formulation development, nevertheless their regulatory use for biowaiver application still require harmonization of the mathematical methods proposed and more detailed recommendations about the procedures for setting up dissolution specifications.     

Review Grain and subgrain characterisation by electron backscatter diffraction

The application of automated Electron Backscatter Diffraction (EBSD) in the scanning electron microscope, to the quantitative analysis of grain and subgrain structures is discussed and compared with conventional methods of quantitative metallography. It is shown that the technique has reached a state of maturity such that linescans and maps can routinely be obtained and analysed using commercially available equipment and that EBSD in a Field Emission SEM (FEGSEM) allows quantitative analysis of grain/subgrains as small as 0.2 m. EBSD can often give more accurate measurements of grain and subgrain size than conventional imaging methods, often in comparable times. Subgrain/cell measurements may be made more easily than in the TEM although the limited angular resolution of EBSD may be problematic in some cases. Additional information available from EBSD and not from conventional microscopy, gives a new dimension to quantitative metallography. Texture and its correlation with grain or subgrain size, shape and position are readily measured. Boundary misorientations, which are readily obtainable from EBSD, enable the distribution of boundary types to be determined and CSL boundaries can be identified and measured. The spatial distribution of Stored Energy in a sample and the amount of Recrystallization may also be measured by EBSD methods.     

A series of energy conserving algorithms for structural dynamics

Abstract

A series of step‐by‐step integration methods has been effectively developed which does not increase the total number of equations of motion and avoids the use of the derivatives of external force. The well‐known Newmark β method [16] with β = 1/4 is the lowest order of accuracy of this series of methods. All the algorithms of this series are unconditionally stable, without overshoot in displacement or in velocity, and they do not possess any numerical dissipations. The rapid changes of dynamic loading can be automatically overcome. It is also verified that the higher the order of the integration method, the more accurate. Consequently, the higher‐order algorithms of this series allow the use of a large time step in step‐by‐step dynamic analysis. Thus, they are competitive in dynamic analysis, especially when the response of a long duration is of interest.     

APPROACHES TO PARAMAGNETIC SEPARATIONS IN BIOLOGY AND MEDICINE

ABSTRACT

Exposure to paramagnetic cations, such as Er³⁺, endows many types of particles with positive magnetic susceptibilities. This discovery has served as the basis for our investigations into methods of separating particulate biological materials magnetically. As part of this enterprise, the “isomagnetic” method has been developed to permit the accurate determination of the magnetic susceptibilities of individual particles. By manipulating the experimental conditions, the particles' magnetic behavior can be controlled to permit the isolation of specific populations of particles from heterogeneous mixtures. Using the Ferro-graph Analyzer, we have applied these principles to the magnetic retrieval and separation of wear particles from human synovial fluid and of various types of eukaryotic and prokaryotic cells.     

MOMENT METHOD OF LOG-NORMAL SIZE DISTRIBUTION FOR COAGULATION PROBLEM: CONSTANT COLLISION KERNEL MODEL

ABSTRACT

The accuracy of the moment method of log-normal size distribution for aerosol coagulation problem was investigated. The constant collision kernel coagulation problem was solved by the moment method as well as a very accurate numerical method (Landgrebe and Pratsinis, 1990) for the purpose. Approximate analytical solutions to the problem by different choices of moments were obtained and compared with the result of the accurate numerical model. During the analysis, solutions to the moments of the size distribution were obtained in exact form and it was discussed that the solutions can be used as a standard reference for ensuring the accuracy of any new numerical schemes for solving the coagulation equation. The time evolution of the particle size distribution was obtained by representing the size distribution with a log-normal size distribution function. Depending on the choice for three moments during the analysis, different solutions to the size distribution parameters were obtained. Three choices for moments were compared as an example. The use of the 0^th, 1^st and 2^nd moments which has been conventionally used was proven to be most accurate for various polydispersity cases by comparing with a numerical result and is recommended to be used for future studies.     

Coupling in Optical Fibres Determined by Improved Variational Approximation

Abstract

Analysis of optical fibre directional couplers is made much more accurate by the application of a new improved approximation. By adding another parameter to the modified Gaussian approximation, we are able to quantify optical fibre directional couplers covering the whole single-mode range in a simple and very accurate way.     

An exact formulation of a filter for rotations in phase gradients and its applications to wavefront reconstruction problems

Abstract

A non-singular and explicit method of constructing a filter exactly for the rotational gradient vector is shown. Such a filter is expected to be useful in phase reconstruction and related problems in adaptive optics with Hartmann sensors. In the deduction of this method, great care is taken in the arrangement of coordinates in order to make the mathematical implementation exact and consistent. The most notable consequence of the deduction is that, after the rotation is eliminated on coordinates shifted a half-period from the original, integral paths should once more be shifted a half-period from the centre of rotations to obtain a consistent wavefront reconstruction. Differences from conventional least methods are shown with experimental results. This formula would be effective for accurate decomposition of the rotation component, which is useful for phase reconstruction and related problems.     

Studies of Newmark method for solving nonlinear systems: (II) Verification and guideline

Abstract

Numerical properties of the Newmark method in the solution of nonlinear systems derived in the accompanying paper are thoroughly confirmed with numerical examples herein. It seems that analytical results can reveal the insight of the Newmark method in the step‐by‐step solution of linear and nonlinear systems. Although the constant average acceleration method is unconditionally stable for linear elastic systems these explorations confirm that it might lead to instability for nonlinear systems. In addition, numerical accuracy for period distortion and amplitude change is also shown to be consistent with the analytical predictions. Therefore, the performance of the Newmark method in the step‐by‐step solution of nonlinear systems is well investigated. As a result, a rough guideline to yield accurate solutions for the use of step‐by‐step integration methods to solve nonlinear systems is proposed.     

Variational Method in the Study of Optical Fibres

Abstract

The dispersion characteristics are needed to evaluate the performance of optical fibres. In general, these will have to be obtained numerically. For this, a computationally fast method is required which will give accurate values of the propagation constants (eigenvalues). In this work, the variation method is used with the propagation equation imposed as a constraint. This method is computationally fast and gives accurate results. In an earlier work, the LP₀₁ mode had been dealt with for the parabolic-profile fibre and it was speculated that the same method could be extended to the higher-order modes. In the present work, the LP₁₁ and LP₁₂ modes have been dealt with by the same method for the parabolic-profile fibre, thus confirming the speculation.     

Quantitative metallography of sigma phase precipitates in AISI 347 stainless steel – a comparison between different methods

Abstract

A reliable method to perform volume fraction measurements of sigma (σ) phase in a niobium stabilised steel (AISI 347) has been developed. The most accurate results of the tested methods were obtained using backscattered electrons in a scanning electron microscope (SEM) and samples etched with oxalic acid. Both optical microscopy (OM) and SEM either on polished samples or on etched samples have been evaluated to come to this conclusion. Several etchants were also tested and careful etching with oxalic acid gave a well defined rim. The measurement of σ-phase fraction has been performed using manual point counting and digital image analysis using manual threshold. It was concluded that image analysis is usually to be preferred since it is faster and also results in higher precision The phase boundary caused by etching was evaluated, and it was found that the boundary area should be included in the measurement when using the recommended SEM method.