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.     

Catalytic square-wave voltammetric detection of DNA with reversible metallopolymer-coated electrodes

Pyrolytic graphite electrodes with adsorbed poly(4-vinylpyridine) (PVP) with attached Ru(bpy)₂²⁺ gave reversible voltammetry, facilitating reusable DNA sensors. These electrodes gave catalytic voltammetric responses to poly(guanylic) acid and DNA at about 0.75 V vs SCE caused by catalytic oxidation of guanine moieties in these polynucleotides. ss-DNA gave twice the square-wave voltammetric catalytic current compared to an equivalent amount of ds-DNA, suggesting that the [Ru(bpy)₂–PVP]²⁺ polymer may be useful for detection of DNA hybridization and damage.     

Background-current subtraction in voltammetric detection for flow-injection analysis

A new approach for background-current subtraction for flow-injection systems using potential-scanning voltammetric detection is described. The method is based on recording voltamperograms while the sample and carrier solutions flow through the cell, and taking the difference as the net response for the sample. Background currents due to hydrogen evolution, oxygen reduction, solvent oxidation or surface processes are thus compensated, and detection limits at submicromolar levels can be obtained. The compensation for oxygen reduction current means that samples do not need to be deaerated. The method has been evaluated for reproducibility, concentration dependence, detection limit, etc. A flow-cell with a stationary disk electrode, a 200-mul sample volume, and rapid differential pulse scanning are used. At a flow-rate of 0.3 ml min about 15 samples can be assayed per hour. Chlorpromazine, phenol, acetaminophen, norepinephrine, lead, cadmium, bismuth and zinc were used as test species.     

Simultaneous determination of multiple components in flow-injection systems by square-wave amperometry

Two or more components can be determined in a single sample by using a flow-injection system with an electrochmical detector, a microprocessor-based potentiostat, and a microcomputer. The computer generates a repeating staircase potential program with a superimposed square wave. Square-wave amperometric measurements at each potential step are used to construct the current/time response at the potential. By appropriate selection of step potentials, the reconstructed response from each step corresponds to the flow-injection response of a particular component. The approach is evaluated by applying it to the simultaneous determination of copper, lead, cadmium and zinc. Limits of detection range from 8 to 18 μg 1^?1. Sample throughput is 80 h^?1.     

Determination of nitrate with a flow-injection system combining square-wave polarographic detection with on-line deaeration

The combination of a flow-injection system with square-wave polarography and on-line deaeration is applied to the determination of nitrate, utilizing the catalytic reaction between nitrate and uranyl ion. The method is simple, rapid (60 samples h^?1), sensitive and accurate, with a detection limit of 2 μM nitrate. The method has been applied to the determination of nitrate in drinking and river waters.     

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.     

Electrochemical behavior and analytical detection of Imidacloprid insecticide on a BDD electrode using square-wave voltammetric method

A sensitive square-wave voltammetric method for the determination of Imidacloprid(IMD) was developed using electrochemically pretreated boron-doped diamond(BDD) electrode. Aqueous solutions were prepared with Confidor 200 SL as the commercial formulation of IMD. Sodium sulfate(Na_2SO_4) was used as supporting electrolyte. The influence of operating parameters, such as the p H of the medium, frequency, pulse amplitude, scan increment and the concentration of IMD was investigated. An irreversible cathodic peak, corresponding to the reduction of IMD is observed at 1.21 V(vs. SCE) and the electrode reaction was controlled by adsorption. Under optimized conditions, the square-wave reduction peak current was linear over the concentration range of(30–200 μmol L~(-1)) with a detection and quantification limits of 8.60 μmol L~(-1))and 28.67 μmol L~(-1)), respectively. The results were compared with spectrophotometry and HPLC methods under some conditions and found to be in good agreement.To investigate applicability to real samples, the proposed method was applied to the determination of IMD in plum juice.     

Anodic square-wave stripping voltammetric analysis of epinephrine using carbon fiber microelectrode

The behavior of epinephrine on a carbon fiber microelectrode (CFME) was studied with cyclic voltammetry and square-wave (SW) stripping voltammetry in order to find optimum conditions for its analysis using the CFME. An anodic stripping peak at about 0.20 V (vs. Ag/AgCl) was utilized. Under optimum conditions for anodic stripping (a pH value of 7.4, a deposition potential of − 0.5 V, a deposition time of 90 s, a final potential of 0.8 V, a SW frequency of 20 Hz, a step potential of 5 mV, and an amplitude of 45 mV), the calibration was linear in the concentration range of 0.0∼0.4 mg/L, and the detection limit was found to be 0.009 mg/L with a relative standard deviation 0.18% (n = 12) at 0.2 mg/L. The analytical performance of the CMFE, which is unmodified, is comparable to or better than other voltammetric results with various modified electrodes.     

Estimation of first-order kinetic parameters by using the extended kalman filter

A model for first-order kinetics is derived for spectra obtained while a reaction is taking place. A technique for nonlinear-regression analysis known as the extended Kalman filter is used to estimate the initial concentrations of the reactants and the rate constant from the spectral data. The effects of the magnitude of the rate constant and the identity of the absorbing species are examined for synthetic spectra containing overlapped responses. The technique is used successfully to obtain the rate constant for the dissociation reaction of a praseodymium complex. The filter is also shown to be useful for the detection of erros in the kinetic model employed to fit the data. The extended Kalman filter can be used to fit kinetic models other than the one discussed here, and may prove to be a valuable technique for estimation of kinetic parameters.     

Voltammetric/amperometric detection for flow-injection systems

A dual-electrode voltammetric/amperometric detector for flow-injection systems is described. The detector provides qualitative voltammetric information without the charging currents associated with scanning the potential. Selectivity is enhanced relative to direct voltammetric detection at a single electrode because only chemically reversible redox couples are detected. A preliminary evaluation with hexacyanoferrate(III) and ascorbic acid is presented.     

Analysis of partially resolved liquid chromatographic peaks using dynamic modeling with the kalman filter

Establishing a calibration model is an important part of any mathematical method for multi-component determination. Use of a calibration model based on single spectra is subject to error, because the model spectrum chosen may not be representative of the response over the full range of the calibration. Alternative calibration models require more time to establish calibration, an these may not be convenient for real-time determinations. A novel calibration method is reported for use with Kalman filters. The method, dynamic modeling, is based on the use of libraries of calibration spectra. The set of used to describe the model at any time is based on component concentrations, estimated for the multi-component mixture, as determined from the Kalman filter, so that several spectra can be used to best describe a varying response. Through application of the dynamic modelingt to simulated and real chromatograms, it is demonstrated that use of the method decreases estimation errors cause by model data mismatches, and that full benefit can be obtained from relatively small libraries.     

Determination of furazolidone in urine by square-wave voltammetric method

A fast, simple and sensitive square-wave voltammetric (SWV) method for the determination of trace amounts of furazolidone (FZ) in urine is reported. A three-electrode system containing stationary mercury dropping (SMDE) working electrode, Pt auxiliary electrode and Ag/AgCl reference electrode was used throughout. Briton-Rabinson buffer solution is used as both pH adjusting agent and supporting electrolyte. The calibration graph showed good linearity in the concentration range of 20–900 ng ml^?1 of furazolidone with a regression coefficient of 0.9996. The equation Δ(i) = 0.0095C_FZ + 0.234 was used for calculation of furazolidone concentration in the sample solution, where C_FZ is the concentration of furazolidone in ng ml^?1 and Δ(i) is the difference between voltammogram peak currents of sample and blank solution. The RSD for 8 replicate measurements of a 60 ng ml^?1 solution and LOD of the proposed method were found to be 2.2% and 5.2 ng ml^?1, respectively. The procedure was successfully applied to the determination of furazolidone in urine samples.     

Simultaneous square-wave voltammetric determination of aspartame and cyclamate using a boron-doped diamond electrode

A simple and highly selective electrochemical method was developed for the simultaneous determination of aspartame and cyclamate in dietary products at a boron-doped diamond (BDD) electrode. In square-wave voltammetric (SWV) measurements, the BDD electrode was able to separate the oxidation peak potentials of aspartame and cyclamate present in binary mixtures by about 400 mV. The detection limit for aspartame in the presence of 3.0x10(-4) mol L(-1) cyclamate was 4.7x10(-7) mol L(-1), and the detection limit for cyclamate in the presence of 1.0x10(-4) mol L(-1) aspartame was 4.2x10(-6) mol L(-1). When simultaneously changing the concentration of both aspartame and cyclamate in a 0.5 mol L(-1) sulfuric acid solution, the corresponding detection limits were 3.5x10(-7) and 4.5x10(-6) mol L(-1), respectively. The relative standard deviation (R.S.D.) obtained was 1.3% for the 1.0x10(-4) mol L(-1) aspartame solution (n=5) and 1.1% for the 3.0x10(-3) mol L(-1) cyclamate solution. The proposed method was successfully applied in the determination of aspartame in several dietary products with results similar to those obtained using an HPLC method at 95% confidence level.     

Osteryoung square-wave voltammetric determination of nicarbazin in chicken tissue

Osteryoung square-wave voltammetric analysis is a rapid technique that can be used to determine nicarbazin residues in chicken tissue. The method is reproducible and can be applied to samples containing as little as 1-10 mug/g nicarbazin. This level of sensitivity is more than adequate for meeting governmental regulations. Osteryoung square-wave voltammetry is significantly faster than classical differential pulse polarography.     

Resolution of strongly overlapped responses in square-wave voltammetry by using the Kalman filter

Various approaches have been proposed for resolving overlapped voltammograms. Such methods have become incresingly important since the advent of small computers and commercial electrochemical instrumentation capable of rapid-scan techniques. The combination of high-resolution, rapid-scan square-wave voltammetry and a linear, recursive estimator known as the Kalman filter is described. Results of the application of this combination to mixtures of thallium(I) and lead(II) in 0.9 M nitric acid are shown. Practical considerations for filter usage such as the choice of models, variances, and initial guesses are discussed, as are limits to the filter. With the Kalman filter, it was possible to quantify thallium in solutions containing as much as a 30-fold excess amount of lead, and it was possible to quantify lead in solutions containing a 60-fold excess amount of thallium. The filter is thus a useful tool for use with empirical models in multicomponent quantitation.     

Modifications to the simplex-optimized adaptive kalman filter

New response functions for the simplex-optimized adaptive Kalman filter have been examined as a means of improving the estimation of known components in the presence of unknown components or other matrix effects. Four response functions based on the innovations sequence have been tested with respect to increasing the computational speed of the filter and reducing the estimation error for the quantitated components. The response function based on the area under the innovations sequence with a penalty function was found to provide the best estimates for synthetic data and ultraviolet-visible spectra.     

Simplex optimization of the adaptive kalman filter

A method for determining concentrations from overlapped spectral data when a complete model is not available is described. This approach combines simplex optimization with the adaptive Kalman filter to yield a method in which initial guesses for the adaptive filter are generated by the simplex algorithm. The performance of the method is demonstrated by deconvoluting overlapped synthetic data and spectral data.     

Determination of phenylpropanolamine and methoxamine using flow-injection with fluorimetric detection

A new flow-injection procedure for the determination of phenylpropanolamine and methoxamine is proposed. The method is based on the derivatization reaction of the primary amine group with o-phthalaldehyde in the presence of 2-mercaptoethanol using fluorimetric detection. The calibration graphs based on peak areas were linear in the ranges 5-200 ng ml(-1) for phenylpropanolamine and 0.2-6 ng ml(-1) for methoxamine. The detection limits were 3.8 and 0.13 ng ml(-1), respectively. The methods were applied to the determination of the drugs in commercial pharmaceutical preparations.     

Formation of two reaction zones in flow-injection systems for kinetic determinations of cobalt and nickel

The injection of a large sample volume (ca. 1 ml) into a single-channel flow-injection system was studied with a dye (to examine physical dispersion) and with chemical systems having easily-controlled reaction rates (to examine chemical kinetics). With the dye, the response curve has a central plateau caused by non-mixing of carrier and sample. When a chemical reaction takes place, two peaks are obtained with a central minimum corresponding to little or no mixing and reaction. Comparison of these two types of response provides relationships of analytical interest between response parameters and variables in te flow-injection system. The configuration is used for individual kinetic determinations of cobalt and nickel (2.5–30 μg ml^?1 based on the rate of their complex formation with 2-hydroxybenzaldehyde thiosemicarbazone. Sample injection rates were 15 h^?1 for cobalt and 40 h^?1 for nickel. Differential kinetic determinations of cobalt and nickel in mixtures are based on the increment in peak height (or area) between the two peaks obtained for each injection; sample throughput is 7 h^?.     

5,5-Diethylbarbiturate tubular electrode for use in flow-injection detection systems

The construction, assessment and pharmaceutical appalications of a tubular potentiometric detector sensitive to the 5,5-diethylbarbiturate anion based on quaternary ammonium salt (tetraoctylammonium5,5-diethylbarbiturate) dissolved in o-nitrophenyl octyl ether immobilized in PVC are described. The intrinsic characteristics of the tubular electrode were determined in a low-dispersion manifold and compared with those of a conventional-shaped electrode with no internal reference solution and incorporating the same sensor. The behaviour of a double-channel flow-injection manifold with the same potentiometric detector was evaluated to assess its applicability to the determination of 5,5-diethylbarbiturate in pharmaceutical preparations. Data obtained in the determination of the anion in the latter matrices are presented and compared with those obtained by the conventional British Pharmacopoeia method.