Kinetic-potentiometric study and analytical applications of micellar-catalysed reactions of 1-fluoro-2,4-dinitrobenzene with amino compounds

The effect of various surfactants on the reaction of 1-fluoro-2,4-dinitrobenzene (FDNB) with amino compounds is examined by using the fluoride-selective electrode. Micellar catalysis was provided by cetyltrimethylammonium bromide (CTABr), Aerosol OS, 22N and 501 and Triton X-405 even at levels below the critical micelle concentration. The micellar catalysis of CTABr in the reactions of 13 amino acids is described and correlation with the structure of the amino acids is discussed. Micellar (CTABr) catalysis of the reaction of FDNB with slowly reacting amines (cephalexin, 2-amino-2-thiazole, sulphamethizole, dopamine and 2-thiobarbituric and 5-nitrobarbituric acids) is described and a kinetic-potentiometric determination (initial slope or fixed time) is proposed for these compounds at concentrations of 10^?4?10^?2 M. The surfactants mentioned can also be determined on the basis of their catalytic effect on the slow reaction of phenylalanine with FDNB. The micellar-catalysed kinetic method is satisfactory for the determination of cephalexin, sulphamethizole and CTABr in pharmaceutical formulations. The fluoride- selective electrode is shown to be useful for studying the liberation of fluoride by organic reactions in micellar systems.     

Alkaline hydrolysis of brilliant green in mixed cationic surfactant systems

Kinetic measurements were performed for the alkaline hydrolysis of brilliant green — a triphenylmethane dye used as a model compound for probing micellar rate effects. This reaction was studied both in the presence of tetradecyltrimethylammonium bromide (TTAB) and tetradecyltriphenylphosphonium bromide (TTPPBr) and also in binary mixtures of these surfactants at different mole fractions of each. All rate surfactant profiles were analyzed using the pseudo-phase model in order to obtain the regression parameters, including binding constants and rate constants in the micellar pseudo-phase. The reaction was catalyzed by both surfactants. The catalytic factor increases from about 10 for pure TTPPBr to about 38 for pure TTAB. Binding of BG to micellar surface is greater in pure TTAB than in pure TTPPBr but significantly reduced in the surfactant mixtures than in pure components. Reduction of the binding constant becomes more significant as the mole fraction of TTAB is increased in the mixture. The kinetic data have been analyzed in terms of models of Piszkiewicz and Raghavan-Srinivasan which are in good agreement.      

Simultaneous kinetic-spectrophotometric determination of sulfide and sulfite by partial least squares and genetic algorithm variable selection

Simultaneous multicomponent analysis is usually carried out by multivariate calibration models such as partial least squares (PLS) that utilize the full spectrum. It has been demonstrated by both experimental and theoretical considerations that better results can be obtained by a proper selection of the spectral range to be included in calculations. A genetic algorithm is one of the most popular methods for selecting variables for PLS calibration of mixtures with almost identical spectra without loss of prediction capacity. In this work, a simple and precise method for rapid and accurate simultaneous determination of sulfide and sulfite ions based on the addition reaction of these ions with new fuchsin at pH 8 and 25°C by PLS regression and using a genetic algorithm (GA) for variable selection is proposed. The concentrations of sulfide and sulfite ions varied between 0.05–2.50 and 0.15–2.00 μg/mL, respectively. A series of synthetic solutions containing different concentrations of sulfide and sulfite were used to check the prediction ability of GA-PLS models. The root mean square error of prediction with PLS on the whole data set was 0.19 μg/mL for sulfide and 0.09 μg/mL for sulfite. After the application of GA, these values were reduced to 0.04 and 0.03 μg/mL, respectively. The text was submitted by the authors in English.     

Application of continuous wavelet transformation to the simultaneous kinetic determination of binary mixtures

Wavelet transformation of kinetic profiles as a new and simple method was developed for the simultaneous determination of binary mixtures without prior separation steps. The mathematical explanation of the procedure is illustrated. Daubechies (db), symlet (sym) and discrete meyer wavelet (meyr) from the family of wavelet transforms were selected and applied under the optimal conditions for the resolution of binary mixtures. A model data as well as experimental data were tested. The results from the experimental data relating to the simultaneous spectrophotometric determination of phosphate and silicate based on the formation of phospho- and silico-molybdenum blue complexes in the presence of ascorbic acid, and also simultaneous determination of Co²⁺ and Ni²⁺ based on their complexation reactions with 1-(2-pyridylazo)-2-naphthol (PAN) in micellar media at pH 6.0 were presented as real models. The proposed method was validated by simultaneous determination of phosphate and silicate in detergent and tap water and also Co²⁺ and Ni²⁺ in tap water samples.     

Stabilization of sulfide and sulfite and ion-pair chromatography of mixtures of sulfide, sulfite, sulfate and thiosulfate

Ion chromatography of sulfide, sulfite, sulfate and thiosulfate in a mixture is often difficult because of instability of sulfide and sulfite, poor separation of sulfide from common anions such as bromide or nitrate and similar elution-times for sulfite and sulfate. An ion-pair chromatographic method for the determination of these sulfur anions has been established by stoichiometric conversion of sulfide and sulfite into stable thiocyanate and sulfate, respectively, prior to the chromatographic run. Sulfate, thiosulfate and thiocyanate were resolved on an octadecylsilica column with an acetonitrile-water mobile phase containing tetrapropylammonium salt (TPA) as an ion-paring reagent, and thiosulfate and thiocyanate in the effluent could be measured with a photometric detector (220 nm) and sulfate with a suppressed conductivity detector. When an acetonitrile-water (6:94, v/v) mobile phase (pH 5.0) containing 15 mM TPA and small amounts of acetic acid was used at a flow-rate of 0.6 ml min(-1), the three anions could be eluted within 32 min. Calibration plots of peak height versus concentration for sulfide (detected as thiocyanate) and thiosulfate gave straight lines up to 35 and 60 microM, respectively. The calibration plot for sulfide coincided with that obtained by using thiocyanate. A calibration plot for sulfite, measured as sulfate, was also linear up to 135 microM and was in accord with that of sulfate. Each calibration plot gave a correlation coefficient greater than 0.999. For six replicates obtained for a mixture of 30.0 microM sulfide, 50.0 microM sulfite, 50.0 microM sulfate and 20.0 microM thiosulfate, the proposed method gave a mean value of 30.1 microM with a standard deviation (SD) of 0.77 microM and a relative standard deviation (RSD) of 2.6% for sulfide, 101 microM (SD = 3.5 microM, RSD = 3.5%) for the total of sulfite and sulfate and 20.1 microM (SD = 0.44 microM, RSD = 2.2%) for thiosulfate. Recoveries for sulfide, sulfite plus sulfate, and thiosulfate in hot-spring water samples using the proposed method were found to be quantitative.     

Simultaneous spectrophotometric determination of cobalt and nickel by partial least square regression in micellar media

Diphenycarbazone has been used for the simultaneous determination of cobalt and nickel by partial least square regression method. DPC complexes of cobalt and nickel at pH 7-10 are of pink color, which are soluble in TX-100 micellar media. A partial least square multivariate calibration method for the analysis of binary mixtures of cobalt and nickel was developed. The total relative standard error for applying the PLS method was calculated. The accuracy and reproducibility of the determination method for various known amounts of Co(II) and Ni(II) in their binary mixtures were tested. The effects of diverse ions on the determination of cobalt and nickel to investigate the selectivity of the method were also studied. The proposed method was applied to the synthetic binary mixtures, alloys and pharmaceutical samples.     

Simultaneous determination of gallium(III) and indium(III) by derivative spectrophotometry

A simple, selective and sensitive derivative spectrophotometric method is proposed for the simultaneous determination of gallium(III) and indium(III) in mixtures using 1-(2-pyridylazo)-2-naphthol in cationic micellar medium, without any prior separation. Beer's law is obeyed between 2.80x10(-1)-3.63 and 4.60x10(-1)-9.20 mug ml(-1) concentration of Ga(III) and In(III) at 550 and 542 nm, the isodifferential points of indium and gallium complexes in the first-order derivative mode, respectively. The proposed method is successfully applied for the determination of gallium and indium in standard reference materials and synthetic binary mixtures with a relative error of +/-2.07 and +/-2.55%, respectively.     

Simultaneous kinetic-spectrophotometric determination of sulfide and sulfite and genetic algorithim variable selection using partial least squares calibration

Simultaneous multicomponent analysis is usually carried out using multivariate calibration models, such as the partial least squares (PLS) one, that utilize the full spectrum. It has been shown by both experimental and theoretical considerations that better results can by obtained by proper selection of the spectral range to be included in calculations. A genetic algorithm (GA) is one of the most popular methods for selecting variables for PLS calibration of mixtures with almost identical spectra without loss of predictive capability. In this work, a simple and precise method for rapid and accurate simultaneous determination of sulfide and sulfite ions based on the addition reaction of these ions with new fuchsin at pH 8 and 25°C using PLS regression and GA for variable selection is proposed. The concentrations of sulfide ions varied between 0.05–2.50 and 0.15–2.00 μg/mL, respectively. A series of model solutions containing different concentrations of sulfide and sulfite were used to check the predictive ability of GA-PLS models. The root mean square error of prediction with PLS on the whole data set was 0.19 μg/mL for sulfide and 0.09 μg/mL for sulfite. After the application of GA, these values reduced to 0.04 and 0.03 μg/mL, respectively. The text was submitted by the authors in English.     

Simultaneous kinetic determination of sulfite and sulfide using artificial neural networks

Artificial neural networks (ANNs) are proposed for the determination of sulfite and sulfide simultaneously. The method is based on the reaction between Brilliant Green (BG) as a colored reagent and sulfite and/or sulfide in buffered solution (pH 7.0) and monitoring the changes of absorbance at maximum wavelength of 628 nm. Experimental conditions such as pH, reagents concentrations, and temperature were optimized and training the network was performed using principal components (PCs) of the original data. The network architecture (number of input, hidden and output nodes), and some parameters such as learning rate (η) and momentum (α) were also optimized for getting satisfactory results with minimum errors. The measuring range was 0.05-3.6 μg ml⁻¹ for both analytes. The proposed method has been successfully applied to the quantification of the sulfite and sulfide in different water samples.     

Simultaneous determination of binary mixtures of sulfonylurea herbicides in water by first-derivative photochemically induced spectrofluorimetry.

First-derivative photochemically induced spectrofluorimetry (PIF-1D) is applied to the simultaneous determination of binary mixtures of 4 sulfonylurea herbicides in aqueous micellar samples. Synthetic binary mixtures of sulfometuronmethyl with chlorsulfuron, metsulfuron-methyl, and 3-rimsulfuron, respectively, are well resolved by using the zero-crossing point procedure. PIF-1D allows the determination of binary mixtures of these herbicides with linear dynamic ranges over about 2 orders of magnitude, limits of detection between 0.5 and 52 ng/mL, and relative standard deviations within 0.3-2.9%. Application to the determination of binary mixtures of these herbicides in spiked tap water samples yielded satisfactory recoveries (90-117%).     

Simple regression model using an optode for the simultaneous determination of zinc and cadmium mixtures in aqueous samples.

An optical-fiber chemical sensor (optode) is described for the simultaneous determination of Zn2+ and Cd2+ mixtures using 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol immobilized onto XAD-4 (Br-PADAP/XAD-4). A simultaneous analysis was achieved by using a single-wavelength kinetic approach coupled with a regression model. Here, the regression model was derived for the slope response of Br-PADAP/XAD-4 to binary mixtures of the metal ions, Zn2+ and Cd2+, at pH 8. The model was used then to predict the concentration of one metal ion while the other was kept constant. This was found to be reasonably successful for Zn2+ and Cd2+, with deviations of 3% and 10%, respectively. The sensor was also found to provide excellent sensitivity for both metal ions with excellent LODs (< 0.1 ppm) and very short analysis times (< 30 s).     

Asymmetric synthesis of L-carnitine from (R)-3-chloro-1,2-propanediol

A practical chemical synthesis of L-carmtine(1) has been accomplished from(R)-3-chloro-1,2-propanediol((R)-4),which is a main by-product originated from(R,R)-Salen Co(Ⅲ) catalyzed hydrolytic kinetic resolution(HKR) of(±)-epichlorohydrin.(R)-4 was utilized as a chiral starting material to prepare the key intermediate cyclic sulfite((R)-S).The new synthetic approach demonstrated an efficient utilization of organic by-product for the asymmetric synthesis of bioactive compounds.     

Evaluation of feed-forward back propagation and radial basis function neural networks in simultaneous kinetic spectrophotometric determination of nitroaniline isomers

Mixtures of 2-, 3-, and 4-nitoroanilines, are simultaneously analyzed with spectrophotometry, based on their different kinetic properties. These nitroanilines react differentially with 1,2-naphtoquinone-4-sulphonate (NQS) at pH 7 in micellar medium to produce colored product. The differential kinetic spectra were monitored and recorded at 500 nm, and the data obtained from the experiments were processed by chemometric approaches, such as back-propagation neural networks (BPNNs), radial basis function neural networks (RBFNNs), and partial least squares (PLS). Experimental conditions were optimized and training the network was performed using principal components (PCs) of the original data. A set of synthetic mixtures of nitroanilines was evaluated and the results obtained by the application of these chemometric approaches were discussed and compared. The analytical performance of the models was characterized by relative standard errors. It was found that the artificial neural networks model affords relatively better results than PLS. The proposed method was applied to the determination of considered nitroanilines in water samples.     

Stopped-flow determination of dipyridamole in pharmaceutical preparations by micellar-stabilized room temperature phosphorescence

The stopped flow mixing technique has been used to study the kinetic determination of dipyridamole by means of micellar-stabilized room temperature phosphorescence (RTP). This mixing system diminishes the time required for the deoxygenation of the micellar medium by sodium sulfite. The phosphorescence enhancers thallium (I) nitrate, sodium dodecyl sulfate (SDS), and sodium sulfite were optimized to obtain maximum sensitivity and selectivity. A pH value of 10.6 was selected as adequate for phosphorescence development. The kinetic curve of dipyridamole phosphorescence was scanned at λ_ex=303 nm and λ_em=616 nm. Then, the intensity at 10 s, and the maximum slope of phosphorescence development, for an interval time of 1 s, were measured. Two determination approaches: intensity and rate methods, were proposed. The calibration graphs were linear for the concentration range from 50 to 400 ng ml⁻¹. The detection limits, according to Clayton et al., Anal. Chem. 59 (1987) 2506, were 21.5 and 37.5 ng ml⁻¹, for intensity and initial rate measurements, respectively. By applying the error propagation theory, the detection limits were 19.0 and 33.0 ng ml⁻¹, for intensity and initial rate measurements, respectively. Two commercial formulations (persantin and asasantin) were analyzed by both proposed methodologies. Adequate recovery values were obtained in both cases.     

Spectrophotometric determination of sulfide in the presence of sulfite and thiosulfate via the precipitation of bismuth(III) sulfide.

A photometric method has been developed for the determination of sulfide at 10(-5) mol dm(-3) levels, which is based on the reaction of sulfide with a given excess amount of bismuth(III) to form a precipitate of bismuth(III) sulfide and on the spectrophotometric measurement of the residual bismuth(III) at 335 nm after extracting with bismuthiol II reagent from an aqueous solution containing acetate buffer into benzene. The presence of sulfite and thiosulfate up to 0.002 mol dm(-3) did not cause any interference in the determination of sulfide, because both sulfite and thiosulfate do not produce any precipitate with bismuth(III). A linear calibration plot with a negative slope was obtained for sulfide over the range of 5.00 x 10(-7) - 3.00 x 10(-5) mol dm(-3) (16.0 - 960 ppb). An experimental calibration plot was in accord with the theoretical plot, taking into account the known excess of bismuth(III), showing that the reaction of sulfide with bismuth(III) proceeded to completion. The relative standard deviation of results from 10 replicate determinations of standard sulfide (2.00 x 10(-5) mol dm(-3)) was 0.44%. The proposed method was successfully applied to the determination of sulfide in hotspring water samples without any pretreatment.     

Micelle-stabilized liquid room-temperature phosphorimetry for metals: The micellar reaction of gallium with 7-iodo-hydroxyquinoline-5-sulfonic acid and its application to the metal determination

The Ga(III)-7-iodo-8-hydroxyquinoline-5-sulfonic acid complex in the presence of suitable micelles and with sodium sulfite as oxygen scavenger exhibited strong phosphorescence at room temperature in aqueous solutions. This micellar reaction provides the basis for a convenient phosphorimetric determination of traces of gallium. Different types of micelles showed their maximum enhancing effects at different pH ranges, affording greater convenience for various analytical purposes. A phosphorimetric procedure with surfactant cetyltrimethylammonium bromide as enhancing agent is proposed. The detection limit for gallium was 5 ng/ml and the calibration graph was rectilinear in the range of 5 to 600 ng/ml. The relative standard deviation was 4% at 50 ng/ml level. The applicability of this room-temperature phosphorimetric procedure to multi-component analyses for the group III elements, Al(III), Ga(III), and In(III), was demonstrated. Kalman filtering was used to deconvolute the phosphorescence spectra of mixtures of aluminium and gallium allowing the simultaneous determination of both metals with satisfactory results.     

Use of ion-selective electrodes in kinetic flow injection: determination of phenolic and hydrazino drugs with 1-fluoro-2,4-dinitrobenzene using a fluoride-selective electrode.

A flow injection (FI) kinetic potentiometric method for the determination of phenolic (acetaminophen and isoxsuprine) and hydrazino (isoniazid) drugs is described. This work shows the usefulness of ion-selective electrodes as detectors in FI systems, not only for direct ion determination but also in routine kinetic analysis. The method is based on the reaction of 1-fluoro-2,4-dinitrobenzene (FDNB) with the analytes in a weakly alkaline medium, which proceeds through the liberation of fluoride from the reagent. The slow reactions with phenols are catalysed by micelles of cetyltrimethylammonium bromide. The reaction rate is monitored with a fluoride-selective electrode in a wall-jet configuration and is used to construct a calibration graph of antilog(delta E/S)-1 versus c (where E = potential, s = slope of the electrode and c = concentration), using the fixed-time approach. The response time and the long-term stability of the electrode were found to be adequate for such kinetic determinations. The proposed method overcomes problems associated with end-point spectrophotometric methods using FDNB and allows measurements in highly coloured or turbid solutions. The optimized method has a linear concentration range of 1 x 10(-4)-50 x 10(-4) mol dm-3, a measurement throughput of 20 or 40 per hour and the precision ranges from 1.8 to 3.6% relative standard deviation (n = 3). Results obtained for commercial pharmaceutical formulations compare favourably with those given by reference methods.     

High performance liquid chromatographic determination of bound sulfide and sulfite and thiosulfate at their low levels in human serum by pre-column fluorescence derivatization with monobromobimane.

A sensitive and specific high performance liquid chromatographic method for the determination of sulfide, sulfite, and thiosulfate was established. Inorganic sulfur anions were converted into fluorescent derivatives with monobromobimane. The derivatives were separated on a coupled column chromatography with a reversed-phase octadecyl silica column connected with a weakly basic anion exchanger column by isocratic elution with acetic acid solution (pH 3)-acetonitrile (13:3, v/v) containing 25 mM NaClO4. The method was applied to the determination of bound sulfide and sulfite and thiosulfate in normal human serum. Thiosulfate could be determined directly by use of an ultrafiltered sample. For the determination of bound sulfide and sulfite, the pretreatment step with continuous flow gas dialysis was effective for the sample after releasing sulfide and sulfite by reduction with dithiothreitol. The limits of quantification by the present method were 0.05 microM for thiosulfate, 0.5 microM for bound sulfide, and 0.2 microM for bound sulfite.     

An ICR study of ion-molecules reactions relevant to titan’s atmosphere: An investigation of binary hydrocarbon mixtures up to 1 Micron

Results are reported for studies of binary mixtures of hydrocarbons exposed to low-energy electron impact ionization. A variety of experimental methods are used: conventional ICR mass spectrometry, the standard double resonance in an ICR for determination of the precursor ions, and the modulated double resonance ejection in an ICR for the determination of the daughter ions. A flowing afterglow-selected ion flow tube experiment (FA-SIFT) was used for validation and examination of termolecular reactions. An extensive database of reaction kinetics already exists for many of these reactions. The main point of this study was the determination of the accuracy of this database and the identification of missing reactions and reaction channels. An effort was made to extend the study to the highest pressures possible to determine if any important termolecular reaction channels were present that were not recognized in earlier investigations. A new approach was used here. In the binary mixtures of hydrocarbon gases, mass spectra were obtained as a function of independent pressure changes of both gases. All the mass peaks in the spectra were fitted using existing kinetic data as a starting point. A model of the ion abundances was then produced from the solution of the partial differential equations derived from the kinetics in terms of reaction rate coefficients and initial abundances. The model was fitted to the data for all of the pressures by a least-squares fit to the reaction rate coefficients and initial abundances. The kinetic parameters were then adjusted if required.     

Picomolar quantitation of free sulfite in foods by means of [57Co]hydroxocobalamin and radiometric chromatography of [57Co]sulfitocobalamin. Method, applications and significance of coexisting sulfides

The concentration dependent reaction of sulfite with 57Co-labeled hydroxocobalamin (OH57CoCbl) to produce a sulfitocobalamin (SO(3)57CoCbl) adduct served as a quantification strategy for foodborne sulfite residues freely extracted into pH 5.2, 0.05 M acetate buffer. SO(3)57CoCbl was then resolved using SP-Sephadex C-25 gel chromatography and its radiometric detection allowed calculation of a standard logit plot from which unknown sulfite concentrations could be determined. The sulfite detection range was 6.0 nM-0.3 pM with respective relative standard deviations of 4.4-29.4% for 50-microl samples. Individual incidences of foodborne sulfite intolerances provoked by L-cysteine or sulfite additive use in bakery products, which remained undetected using conventional sulfite analytical methods, underscored the quantitative value of the method. The analytical significance and occurrences of detectable sulfides coexisting with foodborne sulfite residues was also addressed.