Manifold Parameters Research Articles

Automated flow injection fluorimetric determination and dissolution studies of bumetanide in pharmaceuticals

A novel, sensitive and automated flow injection (FI) method with fluorimetric detection based on the strong fluorescence in alkaline medium has been developed for the assay, content uniformity and automated dissolution studies of bumetanide in pharmaceutical dosage forms. A fully automated FIA system controlled by home-made software (FIA-MOD 2.2.) was used for optimising the chemical and manifold parameters and running of routine measurements. The optimum excitation wavelength for bumetanide is 314 nm and emission wavelength ≥370 nm. The measurement throughput is 60 h −1 using 110 μl sample volume. The useful concentration range is 0.05–10.0 μg ml −1 with an R.S.D. of 0.46% ( n=3; c=1.0 μg ml −1). Common excipients for tablets and injections were found not interfering. The assay results of two commercial drug formulations (tablets and injections) obtained with the proposed method agreed well with those obtained with the current USP method (HPLC-UV detection). Using this automated method the complete dissolution profile of bumetanide tablets was obtained.

Simultaneous determination of nitrite and nitrate in various samples using flow-injection spectrophotometric detection

The direct spectrophotometric method has been developed for the simultaneous determination of nitrite and nitrate by flow-injection analysis. The method is based on the catalytic effect of nitrite on the oxidation of pyrogallol red (PGR) by bromate in acidic media and the decrease in absorbance of the system at 465 nm. The injected sample is split into two streams. One of the streams is directly treated with the above reagents and then is passed to the sample flow cell of the spectrophotometer. The decrease in absorbance at 465 nm is due to the nitrite. The other stream is passed through a reductor micro column containing copperized-cadmium, where nitrate reduces to nitrite and then the sample was treated with the mixed reagents and was passed through the same cell of the spectrophotometer. The total nitrite concentration initially plus that produced was determined. The influence of reagents concentrations and manifold parameters were studied. The effect of potential interfering ions was examined. Nitrite and nitrate can be determined for the range of 0.003–2.00 and 0.030–2.00 μg ml −1, respectively. The sampling rate of analyses was 20±3 h −1, with detection limits 0.001 and 0.010 μg ml −1 for nitrite and nitrate, respectively. Nitrite and nitrate were determined in food and water samples by the proposed method with satisfactory results.

Flow Injection Spectrophotometric Determination of Copper, Iron, Manganese, and Zinc in Animal Feeds Using a Common Manifold

A rapid and simple procedure was developed for the determination of copper, iron, manganese, and zinc in animal feeds using an identical flow injection spectrophotometric manifold but different chromogenic reagents and different detection wavelengths. Bis(cyclohexanone)oxalydihydrazone, formaldoxime, 1,10-phenanthroline, and xylenol orange were adopted as chromogenic reagents for Cu, Mn, Fe, and Zn, respectively. Detection conditions such as manifold parameters, buffer pH, reagent concentration, temperature, and acidity of sample solution were optimized. Analytical characteristics of the method and interference of metal ions commonly present in feeds were studied. By changing the reagents and detection wavelengths, which can be done quickly, the proposed low cost flow injection system can determine Cu, Fe, Mn, or Zn in the range of 0.5-10 mg/L with a sampling throughput of 120/h.

Automated flow-injection spectrophotometric determination of catecholamines (epinephrine and isoproterenol) in pharmaceutical formulations based on ferrous complex formation

A novel automated flow-injection spectrophotometric method for the determination of catecholamines (epinephrine and isoproterenol) has been developed based on the formation of their coloured complexes with Fe(II) in aminoacetic-carbonate buffer pH 8.3 and measuring of the absorbance peaks at the λ max of 530 nm. A fully automated FIA system controlled by home-made software (FIA-MOD) was used for optimising the chemical and manifold parameters and running of routine measurements. The calibration graph was linear in the range of 5–200 mg l −1 for epinephrine with an RSD of 0.24% ( n=5; c=150 mg l −1) and 10–300 mg l −1 for isoproterenol with an RSD of 0.13% ( n=5; c=200 mg l −1). Measurement throughput was 120 h −1 ensuring a sample throughput of 40 h −1 analysed in triplicate. Common excipients for tablets and injections were found not interfering. The proposed method was applied for the assay of various commercial pharmaceutical formulations containing epinephrine and isoproterenol and for the content uniformity test for the isoproterenol tablets. The assay results with RSD 2–4% ( n=3) were comparable with those obtained with the official USP XXIII methods (mean difference 1.9%).

Sensitive and rapid flow injection analysis of sulfonylurea herbicides in water with micellar-enhanced photochemically induced fluorescence detection

A flow injection analysis (FIA) system, combined with micellar-enhanced photochemically induced fluorescence (MEPIF) detection is developed for the sensitive and rapid determination of four sulfonylurea herbicides including chlorsulfuron, metsulfuron methyl, 3-rimsulfuron and sulfometuron methyl in water. The use of micellar solutions of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium chloride (CTAC) as mobile phase provides improved analytical conditions. The FIA manifold parameters, viz, injection volume, flow rate and reactor length were optimized. Calibration plots were linear over 1–2 orders of magnitude. Relative standard deviation ranged from 1.5% to 3.7%. Limits of detection (LOD) were comprised between 0.1 and 1 ng ml −1 according to the compound. The sample throughput was between 56 and 80 h −1. Examples of application to the analysis of these herbicides in spiked river water are given. The mean recoveries ranged from 90% to 106%.

Simultaneous determination of nitrite and nitrate in various samples using flow injection with spectrophotometric detection

A direct spectrophotometric method for the simultaneous determination of nitrite and nitrate by flow-injection analysis has been developed. The method is based on catalytic effect of nitrite on the oxidation of gallocyanine by bromate in acidic media and the decrease in absorbance of the system at 530 nm. The injected sample is split into two segments. One of the streams was directly treated with the above reagents and passed to the sample flow cell of the spectrophotometer. The decrease in absorbance at 530 nm is due to the nitrite. The other stream was passed through a reductor minicolumn containing copperized-cadmium, where reduction of nitrate to nitrite occurs, and then the sample was treated with the mixed reagents and was passed through the same cell of the spectrophotometer. The total nitrite concentration initially plus that produced was determined. The influences of reagent concentration and manifold parameters were studied. The effect of potential interfering ions was examined. Nitrite and nitrate can be determined for the range of 0.010–2.500 μg ml −1 and 0.020–3.500 μg ml −1, respectively. The sampling rate of analysis was 20±3 h −1, with 3σ detection limits of 0.001 and 0.002 μg ml −1 for nitrite and nitrate, respectively. Nitrite and nitrate were determined in food and water samples by the proposed method with satisfactory results.

Determination of iron in soils by flow injection atomic absorption spectrometry

A single‐channel flow injection system was optimized for the determination of available iron (Fe) in soil extracts by atomic absorption spectrophotometry. This method of introducing the samples in the spectrophotometer worked particularly well in preventing blockage of the burner head which was observed in the conventional introduction of Fe for its determination by atomic absorption spectrophotometry. The appropriate selection of the manifold parameters, such as injection volume, tube length and flow rate, allowed introduction of any soil extract without requiring any pre‐treatment. This system allowed determinations at a detection limit of 0.36 mg L‐1 to 5 mg L‐1, with an output of 300 determinations per hour. The results obtained for analysis of 15 soil extracts were in good agreement with those provided by the colorimetric method, with average relative deviations of 1.6%. Relative standard deviations of 4.8, 2.5, and 2.3% were obtained for contents of 1.03, 1.85, and 3.99 mg Fe L‐1, respectively.

Use of mathematical models to describe dynamic behaviour of potentiometric biosensors: Comparison of deterministic and empirical approaches to an urea flow-through biosensor

The response of a flow-through biosensor is the consequence of complex interrelations between the dilution of the sample in a continuous stream (governed by physical variables) and the phenomena involved in the reactions between enzyme and substrate (governed by diffusion and kinetic processes). These interrelations make it difficult to know in advance the influence of manifold parameters in the biosensor response. If a reliable model of these processes is attainable, it will be possible to test rapidly, by computer, the effect of the variation of different operating variables on the response of the biosensor. This paper presents the results obtained when two models are applied to describe dynamic behaviour of a potentiometric flow-through urea biosensor. One of these models uses an empirical approach based on neural networks, while the other proposes a deterministic approach that takes into account reaction-diffusion equations.

A recurrent neural network-based adaptive variable structure model-following control of robotic manipulators

A novel scheme for integrating a neural network approach with an adaptive implementation of variable structure control for multijointed robotic manipulators in complex task executions is presented. The control strategy is developed within the general framework of nonlinear model-following control and attempts to minimize the total regulation time while ensuring a specified percentage of time on the sliding manifolds in order to exploit the disturbance attenuation features present during the sliding motions. These objectives are realized by tailoring an adaptation process that appropriately adjusts the controller gains to keep the motion on the sliding manifolds and also progressively updates the sliding manifold parameters. Rapid execution of the adaptation process is facilitated by a multilayer recurrent neural network. The resulting control scheme is decentralized, and permits design of independent joint controls. A quantitative performance evaluation of the neural network-based adaptive variable structure controller is given in several task scenarios, namely regulation, trajectory tracking and model-following.

Determination of strontium at low concentration levels by flame atomic absorption spectrometry associated on-line with continuous coprecipitation preconcentration

A sensitive method for the determination of strontium has been developed. In this work strontium was determined by flame atomic absorption spectrometry using a continuous copreconcentration dissolution procedure based on the formation of lead sulfate followed by elution with hot EDTA solution. Manifold parameters and chemical conditions are described in detail. A concentration factor of up to 61 can be achieved at a sampling rate of 20–30 h −1. The detection limit for strontium was 0.9 ng ml −1 (3σ) and the relative standard deviation was 3.5% ( n = 8) at a concentration level of 100 ng ml −1.

Determination of arsenic in a nickel alloy by flow injection hydride generation atomic absorption spectrometry

The development of a method for the direct determination of trace arsenic quantities in nickel alloy digests, by flow injection hydride generation atomic absorption spectrometry, is described. An optimization study of the manifold and chemical parameters produced system performance, in terms of tolerance of the nickel matrix and sensitivity, such that matrix removal and pre-reduction of As(V) to As (III) prior to arsine generation were eliminated. Full recovery of the As(V) signal from a solution containing 5 ng ml −1 in the presence of 60 μg ml −1 nickel was obtained. Validation of the method was achieved by analyzing a British Chemical Standard (BCS) Certified Reference Material (CRM) #346 IN nickel alloy containing arsenic at a concentration of 50 μg g −1. Following dissolution in nitric and hydrofluoric acids by a microwave assisted procedure, the only subsequent preparation required was dilution by the appropriate factor. Up to 60 injections h −1 may be made, with a detection limit of 0.5 ng ml −1 arsenic (250 pg absolute) as As(V) in a 500 μl sample. The peak height characteristic concentration is 0.46 ng ml −1, with a relative standard deviation of 3.5% for a 10 ng ml −1 As(V) standard ( n = 6).

Internal Combustion Engine Intake-Manifold Aspiration Dynamics

A model is developed for simulating and predicting the dynamics of intake-manifolds for automotive internal combustion engines. A thermodynamic control volume approach and bond graphs are used to derive mass and energy conservation equations. Simulation outputs include time histories of pressure, temperature, mass flow, energy flow, heat flow and overall volumetric efficiency. Cylinder pressure when the intake valve closes is intensively examined because it determines the volumetric efficiency. Increases in volumetric efficiency result from increases in pressure caused by dynamic effects. Volumetric efficiency versus rpm is used to evaluate the dynamic effects of certain intake-manifold configurations. Major design parameters are the length of the intake manifold pipe, diameter of the intake manifold pipe and length of the pipe upstream of the throttle valve. Changing manifold parameters can yield improvements in volumetric efficiency at certain engine speeds but can also cause deterioration at other speeds. Shortening the length of the upstream pipe moves the volumetric efficiency peaks to higher engine speeds.

LOOP AVERAGES AND PARTITION FUNCTIONS IN U(N) GAUGE THEORY ON TWO-DIMENSIONAL MANIFOLDS

Loop averages and partition functions in the U(N) gauge theory are calculated for loops without intersections on arbitrary two-dimensional manifolds including nonorientable ones. The physical quantities are directly expressed through geometrical characteristics of a manifold (areas enclosed by loops and the genus) and gauge group parameters (Casimir eigenvalues and dimensions of the irreducible representations). It is shown that, from the physical quantities’ point of view, non-orientability of the manifold is equivalent to its non-compactness.

Synthetic control of excited-state properties. Tris-chelate complexes containing the ligands 2,2'-bipyrazine, 2,2'-bipyridine, and 2,2'-bipyrimidine

The photophysical and photochemical properties of the series of tris-chelate complexes Ru(bpy)/sub n/(bpyz)/sub 3-n//sup 2 +/, Ru(bpy)/sub n/(bpym)/sub 3-n//sup 2 +/, Ru(bpym)/sub n/(bpyz)/sub 3-n//sup 2 +/, and Ru(bpy)(bpym)(bpyz)/sup 2 +/ (n = 0, 1, 2, 3; bpy = 2,2'-bipyridine, bpyz = 2,2'-bipyrazine, bpym = 2,2'-bipyrimidine) are described. From the results of temperature-dependent lifetime (210-345 K) and room-temperature emission quantum yield measurements have been obtained: (1) k/sub r/ and k/sub nr/, the radiative and nonradiative decay rate constants for the emitting MLCT manifold and (2) kinetic parameters which suggest the intervention of additional excited states. The significant points of the study are the following: (1) trends in k/sub nr/ properties are understandable based on the energy gap law, (2) low-lying dd states strongly influence lifetimes and photochemical instabilities for the complexes Ru(bpyz)/sub 3//sup 2 +/, Ru(bpym)/sub 3//sup 2 +/, Ru(bpy)(bpyz)/sub 2//sup 2 +/, Ru(bpy)(bpym)/sub 2//sup 2 +/, Ru(bpym)(bpyz)/sub 2//sup 2 +/, Ru(bpym)/sub 2/(bpyz)/sup 2 +/, and Ru(bpy)(bpym)(bpyz)/sup 2 +/ at room temperature, and (3) for the complexes Ru(bpy)/sub 2/(bpyz)/sup 2 +/ and Ru (bpy)/sub 2/(bpym)/sup 2 +/ there is no evidence for low-lying dd states and these and/or related mixed-ligand complexes may provide a basis for a new series of photochemicallymore » stable Ru-polypyridyl chromophores.« less

Free radicals in coal and coal conversions. 5. Methodology for the in-situ investigation of free radicals in coal depolymerization under SRC-II preheater/reactor conditions

In a continuing series of publications, a systematic investigation of the free radicals during coal depolymerization under SRC-II preheater/reactor conditions has been made. A uniquely designed electron spin resonance (e.s.r.) cavity allows the monitoring of free radicals and how they are affected by residence time, temperature and pressure changes. This paper summarizes the methodology that has been developed to study systematically free radical formation and behaviour in-situ during coal liquefaction. The methodology involved is to be used extensively in subsequent papers that examine in detail the manifold parameters that affect coal depolymerization. Also, results are given on the dependence of free radicals on temperature, pressure and gases in the presence of tetralin. The free radical concentration can be measured 3–4 min after the initiation of the heating process to an accuracy of ± 20%, while the process variables may cause several-fold changes in the free radical concentration.