Kinetic-spectrophotometric determination of theophylline,dyphylline, and proxyphylline by use of partial least-squares regression

A kinetic-spectrophotometric method for the determination of theophylline, dyphylline and proxyphylline, based on their azo coupling reaction with the diazonium ion of sulfanilic acid after a treatment with alkali, is proposed. The absorbance is recorded from 340 to 600 nm every second during reaction for 90 s, and calibration is performed by partial least-squares regression, using first derivative spectra values. Mixtures containing 2.5-13 micro g mL(-1) dyphylline and proxyphylline, and 2-9 micro g mL(-1) theophylline were successfully resolved with root mean squared errors of prediction (RMSEP) of 0.4, 0.3, and 0.2 for dyphylline, proxyphylline, and theophylline, respectively. The proposed method was satisfactorily applied to the determination of the three compounds in a commercially available pharmaceutical preparation and provided results similar to those obtained by HPLC.     

Kinetic study and analytical applications of micellar catalyzed reactions of 1-fluoro-2,4-dinitrobenzene with inorganic thioanions using a fluoride-selective electrode

A kinetic study and analytical applications of the CPC micellar catalyzed reactions of 1-fluoro-2,4-dinitrobenzene (FDNB) with inorganic thioanions (sulfide, sulfite and thiosulfafte) using a fluoride-selective electrode is described. Reaction orders (unity for both FDNB and thioanion) and experimental stoichiometric reaction-rate constants were calculated from initial slope measurements (DeltaE/Deltat) at various pH values (4-9). Calibration graphs for quantitative determinations (4.5-45 muM for sulfide, 2.4-75 muM for thiosulfate and 6.6-75 muM for sulfite) are constructed using the initial rate approach. The proposed method has been applied to the determination of sulfide in spiked seawater samples using the multiple standard addition approach with a mean relative error of 5.5%. The application of this micellar catalyzed reaction in the differential kinetic analysis of binary mixtures of sulfide-thiosulfate and sulfite-thiosulfate, using the proportional equations approach at pH 5.5 and 8.0, was unsuccessful due to the interactions of the two analytes, which can be explained using the ion-exchange/pseudophase model of micellar catalysis. However, the use of multiple linear regression approach on a sufficient number of standard binary mixtures can confront this drawback.     

Extraction of the contribution of kinetic profile for reaction of a chemical species in unknown matrices by standard addition method

A new and simple strategy is applied to resolve kinetic profile for the reaction of an analyte in unknown matrices, using standard addition method (SAM). The proposed method uses kinetic spectrophotometric data obtained by standard addition of analyte into unknown mixtures followed by the reaction of analyte with a proper reagent. The proposed method extracts kinetic profile for the reaction of an analyte by averaging the kinetic profiles obtained by subtraction of kinetic profiles after and before standard addition. The rate constant can be obtained using computational curve fitting. The performance of method was evaluated by using synthetic data as well as several experimental data sets. The proposed method can be applied to obtain kinetic profiles of the reactions in the presence of additive interference as well as multiplicative interferences. Hydroxylation reaction of diphenylcarbazide (DPCI) in the presence of diphenylcarbazone (DPCO) as a real system at various pHs was also studied by the present method. The rate constant and the order of the hydroxylation reaction were determined from extracted kinetic profiles.     

Simultaneous determination of iron and ruthenium as ternary complexes by extractive second derivative spectrophotometry

A highly sensitive and selective second derivative spectrophotometric method has been developed for the determination of ruthenium and iron in mixtures. The method is based on the formation of the binary complexes of iron and ruthenium with 4,7-diphenyl-1,10-phenanthroline (bathophenanthroline) in the presence of ethyleneglycol. These complexes are formed at pH 4.0-6.0 upon heating at 90 degrees C for 60 min. The ternary perchlorate complexes are then separated by liquid-liquid extraction. The extracts were evaluated directly by derivative spectrophotometric measurement, using the zero-crossing approach for determination of both analytes. Ruthenium and iron were thus determined in the ranges 9.6-450 and 16.3-280 ng/ml, respectively, in the presence of one another. The detection limits achieved (3sigma) were found to be 2.9 ng/ml of ruthenium and 4.9 ng/ml of iron. The relative standard deviations were in all instances less than 1.5%. The proposed method was applied to the determination of both analytes in synthetic mixtures.     

Simultaneous determination of rifampicin and isoniazid by continuous-flow chemiluminescence with artificial neural network calibration

In this paper a continuous-flow chemiluminescence (CL) system with artificial neural network calibration is proposed for simultaneous determination of rifampicin and isoniazid. This method is based on the different kinetic spectra of the analytes in their CL reaction with alkaline N-bromosuccinimide as oxidant. The CL intensity was measured and recorded every second from 1 to 300 s. The data obtained were processed chemometrically by use of an artificial neural network. The experimental calibration set was 20 sample solutions. The relative standard errors of prediction for both analytes were approximately 5%. The proposed method was successfully applied to the simultaneous determination of rifampicin and isoniazid in a combined pharmaceutical formulation.     

Determination of trimethoprim by the linear absorbances method

The determination of trimethoprim in the presence of dyphylline, proxyphylline, theophylline and caffeine by the linear absorbances method is described. Collinear couples of wavelengths, for the interfering dyphylline-proxyphylline-theophylline-caffeine system (in H₂SO₄, 0.05 mol/L), are provided in order to allow the determination of the analyte in the presence of these interfering substances.     

Simultaneous Spectrophotometric Determination of Paracetamol and P‐Aminophenol by Using Mean Centering of Ratio Kinetic Profiles

A specific spectrophotometric method was developed for simultaneous determination of paracetamol (PCT) and p‐aminophenol (PAP) in water samples without prior separation steps. The method is based on the mean centering of ratio kinetic profiles. Paracetamol and P‐aminophenol react with Fe(III)/hexacyanoferrate(III) complex and result in the formation of colored complex, i.e. Prussian Blue. The differences in the rate of reaction of PCT and PAP with reagents make their simultaneous determination feasible by using mean centering of ratio kinetic profiles. The experimental parameters, such as reagent concentrations and pH were optimized for getting results with minimum errors. The analytical characteristics of the method such as detection limit, accuracy, precision, relative standard deviation (R.S.D.) and relative standard error (R.S.E.) for the simultaneous determination of binary mixtures of p‐aminophenol and acetaminophen were calculated. The results show that the method was capable of simultaneous determination of 0.5–21.0 μg mL⁻¹ and 0.1–15.0 μg mL⁻¹ of PCT and PAP, respectively. The proposed method was successfully applied to the simultaneous determination of paracetamol and p‐aminophenol in several pharmaceutical products and synthetics mixtures.     

Standardless multicomponent qNMR analysis of compounds with overlapped resonances based on the combination of ICA and PULCON

A fast and reliable nuclear magnetic resonance (NMR) method for quantitative analysis of targeted compounds with overlapped signals in complex mixtures has been established. The method is based on the combination of chemometric treatment for spectra deconvolution and the PULCON principle (pulse length based concentration determination) for quantification. Independent component analysis (ICA) (mutual information least dependent component analysis (MILCA) algorithm) was applied for spectra deconvolution in up to six component mixtures with known composition. The resolved matrices (independent components, ICs and ICA scores) were used for identification of analytes, calculating their relative concentrations and absolute integral intensity of selected resonances. The absolute analyte concentrations in multicomponent mixtures and authentic samples were then calculated using the PULCON principle. Instead of conventional application of absolute integral intensity in case of undisturbed signals, the multiplication of resolved IC absolute integral and its relative concentration in the mixture for each component was used. Correction factors that are required for quantification and are unique for each analyte were also estimated. The proposed method was applied for analysis of up to five components in lemon and orange juice samples with recoveries between 90% and 111%. The total duration of analysis is approximately 45 min including measurements, spectra decomposition and quantification. The results demonstrated that the proposed method is a promising tool for rapid simultaneous quantification of up to six components in case of spectral overlap and the absence of reference materials. Copyright © 2015 John Wiley & Sons, Ltd.     

Use of partial least-squares regression for multicomponent determinations based on kinetic spectrofluorimetric data. Simultaneous determination of canrenone and spironolactone in urine

A new spectrofluorimetric method for the simultaneous determination of canrenone and spironolactone in urine is proposed. The method is based on the different rates at which the two analytes react with hot sulfuric acid to form a trienone. The kinetic spectrofluorimetric data are processed by partial least-squares regression. The effects of sulfuric acid concentration and temperature on the system under study were also evaluated and the optimum values for carring out the reaction were 50% and 50 degrees C, respectively. The method was checked by analyzing urine samples that they contained both diuretics. The accuracy and the precision of the method were tested. The relative standard errors in the quantification of each analyte in all tested samples were 3.69 and 3.59%. The proposed method was validated by comparison with a high performance liquid chromatographic method for urine samples.     

串联双柱固相萃取-液相色谱-串联质谱法测定番茄酱中链霉素和双氢链霉素残留量

建立了同时测定番茄酱中链霉素和双氢链霉素残留量的串联双柱净化-液相色谱-串联质谱方法。样品中的残留物用磷酸盐缓冲液(pH 4)提取,经分散固相萃取净化和串联双柱固相萃取净化后,用极性色谱柱在梯度洗脱条件下分离待测物,采用正离子电喷雾离子源(ESI+)在多反应监测(MRM)扫描模式下进行测定,外标法定量。链霉素和双氢链霉素在0.01～0.2 mg/L质量浓度范围内线性关系良好,相关系数(r)大于0.999。链霉素和双氢链霉素的定量限均为0.02 mg/kg,回收率为71%～101%,相对标准偏差为2.3%～15%。该方法操作简便,净化效果好,灵敏,准确,适用于检测和分析番茄酱及其制品中链霉素和双氢链霉素残留量。     

固相萃取-超高效液相色谱-串联质谱法测定蜂产品中10种头孢类药物

建立了蜂产品中10种头孢类药物（头孢喹肟、头孢噻肟、头孢洛宁、头孢哌酮、头孢匹林、头孢氨苄、头孢乙腈、头孢拉定、去乙酰基头孢匹林、头孢唑林）含量的液相色谱-串联质谱测定方法。蜂产品样品中头孢类药物用乙腈-水（80：20,v/v）溶液提取,离心,上清液经Oasis PRIME HLB固相萃取柱净化,氮吹后复溶,进行液相色谱-串联质谱分析。采用Acquity BEH C18色谱柱,以0.1%（v/v）甲酸水溶液-甲醇体系作为流动相进行梯度洗脱,ESI源正离子模式电离,多反应离子监测模式（MRM）检测,基质校准外标法定量。结果表明,10种头孢类药物在一定浓度范围内峰面积与质量浓度的相关系数（r²）大于0.999,线性关系良好;检出限为0.15~1.5 μg/kg,定量限为0.50~5.0 μg/kg;在阴性蜂产品样品中的加标回收率为75.0%~89.8%,相对标准偏差（RSD）为1.4%~4.6%（n=5）。该方法检测周期短,准确度和精密度高,能满足多种蜂产品样品中头孢类药物的检测需要。     

Application of chemometric methods to the simultaneous kinetic spectrophotometric determination of iodate and periodate based on consecutive reactions

A kinetic spectrophotometric method for the simultaneous determination of iodate and periodate in mixtures was proposed. The method is established on the different kinetic behaviours of the analytes which react with starch–iodide in the presence of sodium chloride in sulfuric acid medium. The kinetic data were collected from 260 to 900 nm every 10 nm, within a time range of 0–180 s at 1 s interval, and the absorbance collected at 291, 354 and 585 nm, respectively, increased linearly with the concentration between 0.1–1.2 mg L^− 1 for both iodate and periodate. The mechanism investigation revealed that the iodate/periodate–iodide–starch system is a consecutive reaction. Subsequently, the mathematical model for the quantitative kinetic determination based on the consecutive reactions by utilizing chemometric methods was deduced, and the simultaneous determination of synthetic mixtures of iodate and periodate was then applied. Kinetic data collected at 291, 354 and 585 nm, were processed by chemometric methods, such as classical least square (CLS), principal component regression (PCR), partial least square (PLS), back-propagation artificial neural network (BP-ANN), radial basis function–artificial neural network (RBF-ANN) and principle component–radial basis function–artificial neural network (PC-RBF-ANN). The results showed that calibration model with the data collected at 354 nm had some advantages for the prediction of the analytes as compared with the ones of other two wavelengths, and the PLS and PC-RBF-ANN gave the lower prediction errors than other chemometric methods. The proposed method was applied to the simultaneous determination of iodate and periodate in several real samples; and the standard addition method yielded satisfactory recoveries in all instances.     

A kinetic-dual standard additions method for simultaneous determination of interfering binary mixtures compensated by a synergistic coefficient simultaneous determination of molybdate and tungstate

A kinetic-dual standard additions method for simultaneous determination of interfering binary mixtures is proposed, and the principles discussed. The deviations of the absorbance from additivity in kinetic systems, caused by a synergistic effect between the two catalysts, are effectively compensated with the defined synergistic catalytic coefficient. The hydrogen peroxide-iodide kinetic reaction catalyzed by molybdate and tungstate was studied with a stopped flow injection technique, and the conditions for simultaneous determination of molybdate and tungstate were established. Contents of molybdenum and tungsten in different samples were determined with proposed procedure, the recoveries were 97.6-102.1% and 96.9-98.6%, and the relative standard deviations were 2.3-3.4% and 1.6-2.6% respectively.     

A Sensitive and Selective RP-LC Method for the Simultaneous Determination of the Antihypertensive Drugs, Enalapril, Lercanidipine, Nitrendipine and Their Validation

A RP-LC method is presented, which is sensitive and selective for the simultaneous determination of enalapril–lercanidipine and enalapril–nitrendipine binary mixtures in their pharmaceutical dosage forms. The analyte peaks were detected using the LC method with the mobile phase ratio of methanol: water (70:30 v/v, pH 3.0) and a 1.0 mL min^?1 flow rate. The detection wavelength was selected at 210 nm using photo diode array detector and column temperature was optimized to 30 °C. Linearity was obtained at different concentration ranges for all working pharmaceutically active compounds between 0.5 and 25 μg mL^?1. The proposed methods were extensively validated according to USP 27 requirements and ICH guidelines. The methods were applied to the analysis of pharmaceutical dosage forms containing binary mixtures of enalapril–lercanidipine and enalapril–nitrendipine. Moreover, the proposed methods were applied for the degradation studies of the selected compounds. Degradation studies were conducted using stress conditions such as UV light, acidic and alkaline hydrolysis, oxidation and heat in oven, to evaluate the ability of the separation of the response of standard compounds from their degradation products.     

On-line pervaporation-capillary electrophoresis for the determination of volatile analytes in food slurries

Pervaporation has been coupled on-line to capillary electrophoresis (CE) by a flow injection manifold and the replenishment system of the CE instrument. The approach allows volatile analytes to be removed, derivatisated and injected into the capillary meanwhile the sample matrix remains in the pervaporator. Acetone and four aldehydes (namely: formaldehyde, acetaldehyde, hexenal, 2-trans-hexenal) have been simultaneously determined in slurries samples by this approach. The detection limits (LOD) ranged between 0.1 and 0.6 microg/ml, the quantification limits between 0.5 and 2.0 microg/ml and the linear dynamic ranges between the limit of quantitation and 150 microg/ml. The precision, expressed as relative standard deviation (RSD), ranged between 0.76 and 4.21% for repeatability and between 1.12 and 4.78% for within laboratory intermediary precision. The errors involved in the analysis of the target analytes--expressed as RSD for all compounds--ranged between 0.13 and 4.87%. The optimal pervaporation time and that necessary for the individual separation/detection of the target analytes are 15 and 10 min, respectively. The analysis frequency is 4 h(-1). The accuracy of the method and potential matrix effects were established by analysing spiked samples. Recoveries between 96.12 and 105.67% were obtained. The proposed method was applied to 10 samples with different solid contents (namely, such yoghurt, juice and yoghurt-juice mixtures).     

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.     

Multicomponent kinetic spectrophotometric determination of pefloxacin and norfloxacin in pharmaceutical preparations and human plasma samples with the aid of chemometrics

A spectrophotometric method for the simultaneous determination of the important pharmaceuticals, pefloxacin and its structurally similar metabolite, norfloxacin, is described for the first time. The analysis is based on the monitoring of a kinetic spectrophotometric reaction of the two analytes with potassium permanganate as the oxidant. The measurement of the reaction process followed the absorbance decrease of potassium permanganate at 526nm, and the accompanying increase of the product, potassium manganate, at 608nm. It was essential to use multivariate calibrations to overcome severe spectral overlaps and similarities in reaction kinetics. Calibration curves for the individual analytes showed linear relationships over the concentration ranges of 1.0-11.5mgL(-1) at 526 and 608nm for pefloxacin, and 0.15-1.8mgL(-1) at 526 and 608nm for norfloxacin. Various multivariate calibration models were applied, at the two analytical wavelengths, for the simultaneous prediction of the two analytes including classical least squares (CLS), principal component regression (PCR), partial least squares (PLS), radial basis function-artificial neural network (RBF-ANN) and principal component-radial basis function-artificial neural network (PC-RBF-ANN). PLS and PC-RBF-ANN calibrations with the data collected at 526nm, were the preferred methods-%RPE(T) approximately 5, and LODs for pefloxacin and norfloxacin of 0.36 and 0.06mgL(-1), respectively. Then, the proposed method was applied successfully for the simultaneous determination of pefloxacin and norfloxacin present in pharmaceutical and human plasma samples. The results compared well with those from the alternative analysis by HPLC.     

Determination of bioavailable soluble arsenic and phosphates in mine tailings by spectrophotometric Sequential Injection Analysis

By using a simple Sequential Injection Analysis (SIA) manifold and in base to the kinetic reaction of the molybdenum with As(V) and P(V) was possible to determine As(III), As(V) and P(V) in simple, binary and ternary samples. The activation energies for the reaction between molybdenum and As(V) and P(V) were of 70.90 kJ mol⁻¹ and of 19.02 kJ mol⁻¹, respectively, therefore it was possible to determine both analytes in mixtures by using different reaction temperature. When the analyses were carried out at room temperature, only the P(V) supplied analytical signal; with increased temperature, the kinetics of reaction for As(V) also increased, and a signal was obtained, being 55 °C the optimum temperature. In order to determine As(III), it was oxidized into As(V) with KIO_3, and the reaction was carried out in the same way as for As(V). To resolve mixtures, an equations system from six calibration curves with different sequences of SIA at different temperature was performed. The lineal ranges were between 0.5 μg mL⁻¹ and 10 μg mL⁻¹ with a repeatability and reproducibility between 0.7% and 5.2% and detection limits between 0.36 μg mL⁻¹ and 0.58 μg mL⁻¹. In binary mixtures of P(V)/As(V) the recoveries were close to 100% for both analytes at ratios lesser than 10:1. For As(V)/As(III) ratios between 1:1 and 5:1 the recoveries were ranged between 85% and 95%. The method was applied in mine tailings and in arsenopyrite. The results showed that the soluble arsenic was found oxidized as As(V). These results were compared with those obtained by atomic absorption spectrometry and both proved to be very close.     

Modular stopped-flow/diode-array detection system for simultaneous kinetic analysis

The coupling of a stopped-flow module to a diode-array spectrophotometric detector has been exploited for the simultaneous kinetic resolution of mixtures. The analytical possibilities are shown with the resolution of a mixture of two analytes (hydrazine and phenylhydrazine), yielding products with different spectral features (after reaction with p-dimethylaminobenzaldehyde), so that only the simultaneous measurement of their respective initial rates at their corresponding maximum absorption wavelengths is possible. The method allows 0.02–30 μg ml^?1 hydrazine and 8–2200 μg ml^?1 phenylhydrazine to be determined simultaneously.     

Matrix solid-phase dispersion extraction of organophosphorous pesticides from beeswax

Beeswax is a complex mixture of lipophilic compounds and other components such as aliphatic alcohols and carotenoids. Then, extraction and clean-up for pesticide analysis in beeswax is a challenge. In this work, a multiresidue method for the analysis of dichlorvos (DCV), diazinon, malathion, methyl parathion and coumaphos (CMF) in beeswax was developed. The proposed approach is based on matrix solid-phase dispersion extraction. The adsorbent for sample clean-up was studied and a simplex-centroid cubic statistical design was applied to evaluate pure solvents and their binary and ternary mixtures to elute the analytes. Finally, Florisil and ethyl acetate were chosen as solid support and eluting solvent, respectively. After extraction, pesticides were separated and detected by gas chromatography/mass spectrometry. The method achieved acceptable recoveries (70–85%; except for DCV, 24–38%) with relative standard deviations below 5%. The repeatability of the method was lower than 8% and interday variability was below 12%. The limit of detection (LOD) for the analytes varies between 0.2 and 2.6 µg?kg^?1 and limit of quantification from 0.93 to 8.8 µg?kg^?1. LOD reached for CMF was below the maximum residue limit allowed by the legislation of the United States and Canada.