Recent applications of kinetic methods in multi-component analysis

This review on multi-component kinetic-based determinations covers most publications in this field during the period 2000–2007. The methodologies applied during recent years have been based on differential reaction rates for simultaneous multicomponent analysis. The literature shows a great attempt to apply chemometric methods, such as partial least squares regression, artificial neural networks, H-point standard addition and a new method involving mean centering of ratio spectra in this field. This review also describes some applications of advanced multiway analysis such as PARAFAC and NPLS from 2000 in the multicomponent kinetic analysis.     

Kinetic wavelength-pair method as an alternative approach to simultaneous multi-component analysis

The kinetic wavelength-pair method involves adapting a well established principle to the simultaneous kinetic-based determination of two or more compounds with diode-array detection. It relies on measuring the difference in the rate of change of the absorbance with time at two preset wavelength pairs such that the values of these measuring parameters are the result of the contribution of one or two components. The theoretical basis adapted to first-order kinetic-based determinations was established and checked on four systems. The method thus developed was compared with other differential kinetic methods and applied to the resolution of formaldehyde-acrolein mixtures.     

Simple unsegmented flow configurations for simultaneous kinetic determinations

Two unsegmented-flow manifolds were designed for simultaneous determinations based on differences in the kinetic behaviour of two analytes with the same reagent. The determination of Fe(III) and Co(II) based on displacement of Fe(III) and Co(II) from their EGTA complexes by PAR, was used as a model system. The displacement reactions were photometrically monitored at 510 nm.     

Simultaneous kinetic determinations with the kalman filter

The linear Kalman filter is successfully applied to the processing of data for simultaneous kinetic determinations. The Kalman filter offrs all of the advantages of linear least squares over traditional methods of data processing, but is simpler and more efficient than batch-mode least squares. The viability of the Kalman filter is demonstrated with synthetic data and it is then applied to the analysis of amino acid mixtures by their reaction with trinitrobenzenesulfonic acid. Mixtures of glycine and asparagine are successfully analyzed even though their pseudeo-first-order rate constants differ by a factor of only 2.5. The potential of the Kalman filter for real-time application is discussed.     

Kinetic study of competing first-order processes: simultaneous quantification of hemoglobin and methemoglobin in whole blood

The development and evaluation of a kinetic method for the simultaneous quantification of methemoglobin and hemoglobin is described. A unique feature of the reaction/monitoring system is that the two species produce signals that change in opposite directions. Attempts to optimize the reaction conditions, procedures for preparing reliable standards, a new multiwavelength method used for comparison purposes and results for synthetic standards and blood samples to which known amounts of methemoglobin are added are described. Combined effects of competing directions of signal change, large concentration differences and conditions required for pseudo-first-order behavior results in a relativity narrowly defined set of conditions that permit simultaneous determinations. Even so, results for methemoglobin were in reasonable agreement between the kinetic and spectrophotometric methods (slope 1.05, intercept 0.17 mmol l^?1); difficulties in achieving pseudo-first-order behavior yielded less reliable results for hemoglobin with a least-squares slope of 1.16 for a comparison of results by kinetic and spectrophotometric methods. This latter problem had an adverse effect on comparison of percentages of methemoglobin in samples even though concentration values were in good agreement.     

Catalytic kinetic simultaneous determination of iron, silver and manganese with the Kalman filter by using flow injection analysis stopped-flow spectrophotometry

A catalytic differential kinetic method with Kalman filter for the simultaneous determination of multi-component is described. The oxidization of Rhodamine B (RB) by potassium periodate in a slightly acid solution is a slow reaction. But iron(III), silver(I) or manganese(II) has a differential catalytic effect on the oxidation reaction of RB in the presence of 1,10-phenanthroline as the activator. So iron, silver and manganese can be simultaneously determined by measuring the decreasing absorbance of the dye (RB) at 555 nm. A flow injection analysis stopped-flow spectrophotometric system with a microcomputer performs the determinations. This method has been applied to determining iron, silver and manganese of alloy samples with satisfactory results.     

Kinetics in continuous flow sample processing Chemical Contributions to Dispersion in Flow-Injection Techniques

A numerical model based on a basic dispersion equation modified by simultaneous consideration of the chemical effect introduced by a chemical reaction taking place as the sample plug disperses has been tested. Computer analysis and simulation (by use of an alternating direction implicit finite difference approximation) by solving the laminar dispersion equation and the rate expression simultaneously, have been evaluated with experimental studies of a reaction of moderate speed (oxidation of ascorbic acid by dichromate ion). Theoretically generated signal profiles indicated the need for three correction factors representative of the deviation of the experimental system from ideality. The rate coefficient in the chemical kinetic term (if pseudo-first-order is assumed) appears to change in an oscillating manner reflecting the complexity of the overall kinetic process. A straight-line relationship was found between the time at peak maximum and the rate coefficient in computer-simulated curves. Such a correlation provided a way to estimate a value for the rate coefficient of the L-ascorbic acid/dichromate reaction which agreed with the one obtained from batch kinetic determinations. In some of the cases studied, the unbalanced evolution of dispersion forces resulted in chemically induced doubled-humped peaks.     

Kinetic Methods of Analysis: How Do They Rate?

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 cmerged 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 multiple 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.     

Improved trihydroxyindole method for the simultaneous stopped-flow spectrofluorimetric determination of epinephrine and norepinephrine in urine

A modification of the trihydroxyindole method for the simultaneous fluorimetric determination of epinephrine and norepinephrine in urine is reported. The overall reaction (oxidation and tautomerization) develops in a single step and the lutins formed are monitored by the stopped-flow technique. The determinations are based on the initial rate and fluorescence amplitude of the kinetic curves. An extension of the proportional equations method is used for the simultaneous resolution of the two catecholamines. The linear range of the proposed method is 0.1–460 ng ml^?1 for epinephrine and 0.2–480 ng ml^?1 for norepinephrine and the analytical recoveries are about 95% and 91%, respectively. The proposed method offers simplicity, improved sensitivity and a low, steady reagent blank signal.     

Use of a stopped-flow/T-format spectrofluorimeter for simultaneous kinetic analyses

The potential of the joint use of a T-format spectrofluorimeter and the stopped-flow mixing technique in simultaneous kinetic determinations was studied. For this purpose, the direct resolution of a mixture of two analytes (neomycin and promethazine), by use of a condensation and an oxidation reaction that yield reaction products with similar maximum excitation wavelengths but different emission wavelengths was chosen. The determination was readily accomplished in a few seconds by simultaneously measuring the respective initial rates in the corresponding emission channels. Mixtures of neomycin and promethazine in ratios between 8:1 and 1:9 were thus satisfactorily resolved. The relative standard deviation was 1.0–1.8%. The proposed method was applied to the analysis of a commercially available pharmaceutical preparation, with a recovery of 99.3–102.0% for neomycin and 88.8–93.0% for promethazine.     

Simultaneous spectrophotometric determination of paracetamol and salicylamide in human serum and pharmaceutical formulations by a differential kinetic method

A rapid, simple, and sensitive differential kinetic method is presented for the determinations of acetaminophen (also known as paracetamol) and salicylamide. The method is based on their oxidation reaction by Fe3+ ion in the presence of 1, 10-phenanthroline as indicator. The reactions can be monitored spectrophotometrically by measuring the increase in the absorbance of the solution at 510 nm. Two times were selected one in which only paracetamol is oxidized by Fe3+ ion and the other in which both drugs are oxidized by Fe3+ ion. The data were evaluated by the proportional equations method. The method allowed the simultaneous determination of paracetamol and salicylamide at concentrations between 0.5-20 and 1-40 microg/mL with relative standard deviations of 3.47 and 2.58%, respectively. The method was applied to the simultaneous determination of paracetamol and salicylamide in human serum and pharmaceutical formulations.     

Dual capillary gas chromatographic analysis of alcohols and methyl tert-butyl ether in gasolines

A gas chromatographic method has been developed for the identification and direct determination of alcohols and methyl tert-butyl ether (MTBE) in gasolines. The technique involves simultaneous injection of the gasoline without any sample preparation onto two fused silica capillary columns of differing polarities. The method permits simultaneous determinations of methanol, ethanol, 2-propanol, tert-butanol, 1-propanol, sec-butanol, 1-butanol, and MTBE. By using an automatic sampler in combination with electronic pressure programming and BASIC programming, the determinations were performed automatically and reproducibly with a relatively short analysis time.     

胶束介质在动力学分析中的应用

评述了胶束介质在动力学分析测定中的作用和应用状况，讨论了胶束催化的动力学特征，胶束对反应物理化学性质的修饰及其在动力学多组份测定和酶催化动力学分析中的应用。     

Multicomponent kinetic determinations using multivariate calibration techniques

Multivariate calibration techniques for use in multicomponent kinetic-based determinations are reviewed. Multivariate calibration is a chemometric tool that continues to grow in popularity among analytical chemists. Multicomponent kinetic methods depend on differences in rates of reactions or processes to distinguish among the components. Kinetic profiles or a combination of kinetic profiles and spectra are commonly used. Because of their ability to process large quantities of data, multivariate calibration techniques are well suited for kinetic-based determinations. The concepts and principles of multivariate calibration are discussed first. Classical least squares regression, principal component regression, partial least squares regression and artificial neural networks are the multivariate calibration techniques considered here in detail. Recent examples of the application of these techniques to multicomponent kinetic determinations are reviewed. Both single and multiwavelength kinetic data are considered.     

Spectrophotometric flow-injection techniques for the multicomponent monitoring of process streams

An overview of simultaneous determinations in flow-injection analysis (FIA) is presented and the advantages of photodiode array detection are discussed. The application of multivariate calibration procedures to nonselective data is outlined and examples of its use in FIA are reviewed. The role of flow-injection techniques in process analysis and the potential of FIA-photodiode array-multivariate calibration systems for on-line multideterminations are also considered.     

主成分分析-紫外光谱法同时测定四种维生素B

采用主成分分析法(PCA)完成对多组分样品分析的建模及解析研究,用于处理紫外光谱数据,实现了维生素B_1、B_2及B_6及烟酰胺四组分的同时测定,结果可靠,操作简便。     

有机金属化合物中碳氢钼(锌)同时快速微量测定研究

由于某些有机金属化合物很不稳定,制取困难,获得量甚少,因此迫切需要建立相应的快速分析方法,并尽可能利用一份样品测出多种元素含量,以判断化合物的组成或纯度。虽然有机金属化合物(包括原子簇化合物)中碳、氢和金属的同时快速测定法已有报道,但是,某些有机钼(锌)化合物在高温燃烧氧化过程中,能生成挥发性的金属氧化物,并随着载气吹离样品舟,故不能简单地以高温氧化分解和称样品舟中残渣的方法来进行快速同时测定。本文对Gawargious等人建     

Combined kinetic analysis of thermal degradation of polymeric materials under any thermal pathway

Combined kinetic analysis has been applied for the first time to the thermal degradation of polymeric materials. The combined kinetic analysis allows the determination of the kinetic parameters from the simultaneous analysis of a set of experimental curves recorded under any thermal schedule. The method does not make any assumptions about the kinetic model or activation energy and allows analysis even when the process does not follow one of the ideal kinetic models already proposed in the literature. In the present paper the kinetics of the thermal degradation of both polytetrafluoroethylene (PTFE) and polyethylene (PE) have been analysed. It has been concluded, without previous assumptions on the kinetic model, that the thermal degradation of PTFE obeys a first order kinetic law, while the thermal degradation of PE follows a diffusion-controlled kinetic model.     

Some observations on the analytical utility of a fluorometric stopped-flow method for resolution of histidine and 1-methylhistidine mixtures

The fluorescent reactions of histidine and 1-methylhistidine with o-phthaldialdehyde and 2-mercaptoethanol are exploited for the individual and simultaneous determination of these compounds by the stopped-flow technique. The instrumental setup used consists of a stopped-flow module coupled to a conventional fluorescence spectrophotometer. The parameters used for these determinations are the initial rate and the fluorescence amplitude of the kinetic curves. Linear ranges, precision, and the results of the selectivity studies are reported. An extension of the proportional-equations method is used to resolve histidine: 1-methylhistidine mixtures in ratios between 3:1 and 1:8. The method is very simple, inexpensive, and fast (only about 10 sec is required for initial-rate measurements, and about 90 sec for those of signal amplitude).     

Rapid Determination of Aldehydes in Air Analyses

Abstract

A simple analytical method for aldehyde determinations in ambient air is described. The method involved trapping the aldehydes as their DNPH derivatives in acetonitrile solution and then direct injection and analysis of the resulting solution on a reversed phase HPLC column with simultaneous detection at 254 and 360 nm. Several comparison studies are described.