Stopped-flow, air-segmented continuous flow: kinetic determinations of glucose and phosphate in wine and serum samples

Hsieh, Yunsheng; Crouch, S. R.

doi:10.1016/0003-2670(93)80019-h

Cited by 10 publications

(1 citation statement)

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“…The derivatization step is based on a redox reaction, mainly with a copper salt (Yerba et al, 1993; Araujo et al, 2000; PerisTortajada et al, 1992), or using immobilized enzymes [such as glucose oxidase (Yokoi et al, 1995;Matsumoto et al, 1991;Schuhmann, 1991), glucose dehydrogenase (Appelqvist and Hansen, 1999) or mannitol dehydrogenase (Kiba et al, 1991)] packed in a reactor. Photometric detection of the reaction products is mainly used (Araujo et al, 2000;Peris-Tortajada et al, 1992;Yokoi et al, 1995;Hsieh and Crouch, 1993;Hartmann et al, 1994;Oliveira and Fatibello-Filho, 1999), but other alternatives such as amperometry (Appelqvist and Hansen, 1999;Matsumoto et al, 1991;Kiba et al, 1991), fluorimetry (Schuhmann, 1991), or atomic spectroscopy (Lopes et al, 1995) have also been used. Average errors of these methods are about 7% and all them present good precision (RSD= 0.4%-3.9%).…”

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Analytical Methods in Wineries: Is It Time to Change?

Castro

Pérez-Juan²

2005

Food Reviews International

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A review of the methods for the most common parameters determined in wine-namely, ethanol, sulfur dioxide, reducing sugars, polyphenols, organic acids, total and volatile acidity, iron, soluble solids, pH, and color-reported in the last 10 years is presented here. The definition of the given parameter, official and usual methods in wineries appear at the beginning of each section, followed by the methods reported in the last decade divided into discontinuous and continuous methods, the latter also are grouped in nonchromatographic and chromatographic methods because of the typical characteristics of each subgroup. A critical comparison between continuous and discontinuous methods for the given parameter ends each section. Tables summarizing the features of the methods and a conclusions section may help users to select the most appropriate method and also to know the state-of-the-art of analytical methods in this area. Keywords Parameters, Official methods, Usual methods, Non chromatographic methods, Chromatographic methodsWine is a product with a very complex composition. Among the large number of substances found in wine, many are at very low concentrations even though they play a main role in wine characteristics, evolution, and/or quality. A complete analysis of wine is a time-consuming process, but it yields the necessary information for both elaboration of a quality product and conservation under proper conditions. Usually, the number of parameters to be analyzed is simplified as a function of the aim, the commonest being either to know the evolution of the process or to fulfill food laws. The more detailed the analysis is, the better knowledge of the wine is achieved, but a compromise between time and information requirements must be established in order to guarantee a given quality with minimum cost. Therefore, only a few parameters are periodically checked. Between them, the most common are: soluble solids, reducing sugars, alcoholic degree, pH, total and volatile acidity, sulfur dioxide, color, polyphenol index, iron, and organic acids.Most analytical methods for monitoring wine composition recognized by the international community as official methods of analysis are manual methods with high robustness and precision, even though more recent methods may be based on modern automated instrumental techniques. Nevertheless, the manual methods are slow, tedious, and require a high level of human participation. Thus, their application is a balance between the number of parameters required for monitoring wine production, frequency of analysis, and cost of human and material resources. The new faster methods, which usually have the appropriate sensitivity, selectivity, and precision, can circumvent the problem created by the large number of samples to be analyzed in order to guarantee proper monitoring of wine production. In the last 10 years, rapid and high sample throughput methods of analysis have been developed. It is interesting to know the features of these new methods-mainly in terms of accuracy and preci...

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confidence: 99%

Analytical Methods in Wineries: Is It Time to Change?

Castro

Pérez-Juan²

2005

Food Reviews International

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Instrumentation for Kinetics

Cordos

2000

Encyclopedia of Analytical Chemistry

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In kinetic methods or reaction‐rate methods of analysis, the rate of a given reaction is measured and related to the concentration of the sought‐for species. The instrumentation in kinetics is primarily designed to monitor the evolution of the analytical signal with time. Unlike in the traditional equilibrium‐based approaches, where the signal is measured after the reaction has reached completion, in kinetic methods the signal is usually measured in the first few percent of the total reaction time. Therefore, the advantages and limitations of kinetic methods should be considered in their relations with equilibrium methods. Kinetic methods are faster than equilibrium‐based methods since the user does not have to wait for a reaction to go to completion. They are relative methods that depend on changes in concentration and not on its absolute value and they could be more selective than equilibrium methods since the difference between reaction constants could be used to discriminate against an interfering species. The limitations of kinetic methods are a lower precision and a strong dependence on experimental conditions. The main factors that cause these limitations are the measured signal, which is small in comparison with that from an equilibrium reaction, and the dependence of rate constants on temperature, pH, ionic strength, etc. Therefore, the measurement systems used in kinetic methods should be sensitive and the experimental conditions should be kept strictly constant. The best results in kinetic methods are obtained with instrumental systems having a high degree of automation. The main operations that should be carried out by the instrumentation in kinetic determinations are the mixing of the reactants, measurement of the detector signal in time and processing of data to obtain the reaction rate and concentration. The mixing of the reactants should be done in a time shorter than the reaction half‐life and it is critical for fast reactions where required mixing times are of the order of milliseconds. In these cases the mixing is accomplished by mechanical systems that rapidly drive the reactants through a mixing chamber into an observation chamber. For slower reaction the best mixing procedures are based on automated flow analyzers that have different manifolds configurations adapted both to sample processing and to reactant mixing. After mixing, the reaction could be monitored in time either by stopping the flow and recording the signal or by passing the reacting plug several times through the detector and reading the signal after each pass. The measurement of the detector signal, after the reagents are mixed, could be done with a large variety of detectors, but the most commonly used detection systems are photometric and electrochemical. Photometric detection provides a short response time, specificity and the possibility of collecting full spectra very rapidly if photodetector arrays are used. Electrochemical detectors are simple and relatively inexpensive. The concentration of the analyte is determined from the slope of the detector signal. In many routine procedures the slope is determined by measuring the signal at one or two fixed points in time or by determining the time required by the signal to reach a predetermined level. These procedures have the advantage that they are rapid and need no supplementary instrumentation for data processing. Another approach in kinetic data processing, based on computer software, computes a curve that fits the experimental data. The slope or concentration is then extracted from the mathematical expression of the fitting curve.

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Kinetic Methods of Analysis: How Do They Rate?

Crouch

1994

J Chinese Chemical Soc

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During the past few years there has been a resurgence of interest in kinetic aspects of analytical chemistry and in kinetic methods of analysis. The increased activity is a result of advances that have been made in instrumentation and in data processing techniques. Still, the kinetic approach is not widely applied by practicing analytical chemists. Why is this true? Why are kinetic methods not among the most common methods in use by analytical chemistry? This paper discusses the advantages and limitations of kinetic methods and addresses the probable reasons that they are not widely used. Several new principles have emerged that are guiding the development of new kinetic-based determinations. These developments have made it possible to compensate for errors that result from changes in reaction conditions and to determine accurately rnultiple components in mixtures. With these advances kinetic methods are approaching the reliability of traditional equilibrium-based determinations and should be re-evaluated by analytical chemists.lln"lQ,lII

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Stopped-flow, air-segmented continuous flow: kinetic determinations of glucose and phosphate in wine and serum samples

Cited by 10 publications

References 26 publications

Analytical Methods in Wineries: Is It Time to Change?

Analytical Methods in Wineries: Is It Time to Change?

Instrumentation for Kinetics

Kinetic Methods of Analysis: How Do They Rate?

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