Application of a modified simplex method to the multivariable optimization of a new FIA system for the determination of osmium

A methodology based on the coupling of experimental design and a modified simplex method is proposed for the optimization of a new flow injection-kinetic system for the spectrophotometric determination of Os (IV) with m-acetylchlorophosphonazo, which has for the first time been used as chromogenic reagent in the quantitative analysis of this element. An orthogonal array design is utilized to design the experimental protocol, in which six variables are varied simultaneously, and obtain the initial simplex using 25 experiments. A modified simplex method is applied to continuously optimize the data of the orthogonal array design; the search for optimum conditions of ¶6 variables using the modified simplex method required only 25 experiments. The efficiency and simplicity of the coupling of the experimental design and the modified simplex method are attractive for the development of new analytical methods. The method has been applied to the determination of Os (IV) in a refined ore as well as in a secondary alloy and provided satisfactory results.     

Four-level orthogonal array design as a chemometric approach to the optimization of polarographic reaction system for phosphorus determination

It is the purpose of the present work to provide information on the four-level orthogonal array design and data analysis for the optimization of analytical procedures. In the theoretical part, the construction and characteristics of the OA(16)(4(5)) matrix is described in detail, followed by the data analysis strategy, in which the significance of the different factors is quantitatively evaluated by an analysis of variance (ANOVA) method including per cent contribution, and the difference among four levels for each factor is determined by Duncan's multiple F test. Furthermore, a third-order polynomial model representing response surface is established to estimate the effects for the factors with significant influences. In the application part, the proposed four-level orthogonal array design and data analysis method were applied to optimize polarographic reaction system for phosphorus determination. By conducting 16 preplanned experiments that span the maximum working range of the system, the best experimental conditions for achieving the largest response can be obtained. The expected value for each experimental trial calculated by the third-order regression equation established is in good agreement with the corresponding experimental value. To confirm the validity of the optimization procedure, additional experiments using the recommended conditions were performed. The results demonstrate that satisfactory results can be acquired. Therefore, the proposed four-level orthogonal array design as a chemometric approach to optimize the polarographic reaction system for phosphorus determination is rather efficient and effective.     

试验设计与优化方法

本文介绍了作者所在研究小组多年来在试验优化方法方面的研究工作，内容涉及正交试验设计、单纯形优化法、均匀设计法、回归正交设计和模糊正交设计、人工神经网络等多种试验优化设计方法的应用，优化效果的综合评价，多种试验优化设计方法的综合应用等     

Application of artificial neural networks in multifactor optimization of an FIA system for the determination of aluminium

A methodology based on the coupling of experimental design and artificial neural networks (ANNs) is proposed in the optimization of a new flow injection system for the spectrophotometric determination of Al(III) with Arsenazo DBM, which has for the first time been used as chromogenic reagent in the quantitative analysis of aluminium. An orthogonal design is utilized to design the experimental protocol, in which three variables are varied simultaneously. Feedforward-type neural networks with faster back propagation (BP) algorithm are applied to model the system, and then optimization of the experimental conditions is carried out in the neural network with 3-7-1 structure, which have been confirmed to be able to provide the maximum performance. In contrast to traditional methods, the use of this methodology has advantages in terms of a reduction in analysis time and an improvement in the ability of optimization. The method has been applied to the determination of Al(III) in steel samples and provided satisfactory results.     

Application of artificial neural networks in multifactor optimization of an FIA system for the determination of aluminium

A methodology based on the coupling of experimental design and artificial neural networks (ANNs) is proposed in the optimization of a new flow injection system for the spectrophotometric determination of Al(III) with Arsenazo DBM, which has for the first time been used as chromogenic reagent in the quantitative analysis of aluminium. An orthogonal design is utilized to design the experimental protocol, in which three variables are varied simultaneously. Feedforward-type neural networks with faster back propagation (BP) algorithm are applied to model the system, and then optimization of the experimental conditions is carried out in the neural network with 3-7-1 structure, which have been confirmed to be able to provide the maximum performance. In contrast to traditional methods, the use of this methodology has advantages in terms of a reduction in analysis time and an improvement in the ability of optimization. The method has been applied to the determination of Al(III) in steel samples and provided satisfactory results. Received: 26 May 1999 / Revised: 29 July 1999 / Accepted: 17 August 1999     

Optimization of the micellar electrokinetic capillary chromatographic determination of dauricine and daurisoline in Rhizoma Menispermi and its herbal medicine using experimental design and radial basis function neural network

Orthogonal design has been applied to the optimization of separation and determination of dauricine and daurisoline in Rhizoma Menispermi and its herbal medicine by micellar electrokinetic capillary chromatography. Operational variables, such as the voltage, micelle concentration, buffer concentration and pH were optimized. Their different effects on peak resolution were studied by the experimental design method. Optimized separation conditions were obtained and successfully applied to the separation and determination of dauricine and daurisoline in real samples. The proposed method allows alkaloids in real samples to be determined within 15 min using a buffer system composed of 25 mM HAc, 25 mM NaAc and 2% polyoxyethylene sorbitan monolaurate (Tween-20) (pH 4.5). In addition, a radial basis function neural network with a “4-18-1” structure was developed based on the experimental results of orthogonal design and uniform design, and applied to the prediction of peak resolution of dauricine and daurisoline under the optimum separation conditions given by orthogonal design. The predicted results were in good agreement with the experimental values, indicating that radial basis function neural network may be a potential method for the selection of separation conditions in capillary electrophoresis.     

偶氮氯膦-mA-锇-高碘酸钾催化光度法测定微量锇

在碱性介质中,锇（Ⅳ）对KIO4氧化偶氮氯膦－mA的褪色反应有明显的催化作用,据此建立了催化光度法测定微量锇（Ⅳ）的新方法,并用正交实验设计对反应条件进行了优化。方法的检测限为2．0μg/L。锇（Ⅳ）含量在7．0－25．0μg/L范围内服从比尔定律。此方法已用于贵金属精矿和二次合金中微量锇的测定,相对误差均为0．9％,回收率在95．38％－106．0％之间。     

Optimisation of sensitivity in the multi-elemental determination of 83 isotopes by ICP-MS as a function of 21 instrumental operative conditions by modified simplex, principal component analysis and partial least squares

The optimisation of the sensitivity in the ICP-MS determination of 83 isotopes, as a function of 21 operative parameters was performed by generating an initial experimental design that was used to define, by principal component analysis, the multi-criteria target function. The first PC, which contained an overall evaluation of the signal intensity of all isotopes, was used to rank the experiments. The modified simplex optimisation technique was then applied on the ranked experiments. The increase in signal intensity was, on the average, 3.9 times for the isotopes considered for the simplex procedure. When finally convergence was achieved, a PLS regression model calculated on the available experiments allowed to investigate the effect played by each factor on the experimental response. Simplex and PCA proved to be extremely effective to obtain the optimisation and to generate the multi-criteria target function: they can be suggested as an automatic method to perform the optimisation of the instrumental operative conditions.     

Use of highly efficient Draper-Lin small composite designs in the formal optimisation of both operational and chemical crucial variables affecting a FIA-chemiluminescence detection system

A new formal strategy in the multidimensional optimisation of the experimental variables affecting the chemiluminescence (CL) detection in flow injection analysis (FIA) is proposed here. The strategy implies several steps, being the most significant: selection of the variables to be studied and their experimental domain; use of a screening design to detect significant variables and interactions into the experimental region; study of the main effect of variables and second-order interactions; and finally application of a Draper-Lin small composite design (orthogonal) to obtain the optimum values of the significant variables. The methodology is applied to the determination of methylamine by FIA based on the use of the peroxyoxalate CL (PO-CL) reaction. Considering the high number of experiments required due to the different chemical and instrumental variables to be taken account and their adequate compatibility to obtain maximum sensitivity, the methodology offers a rigorous study of the main effects and interactions, achieving a reduction of experimental work.     

A sequential injection spectrophotometric method for the determination of penicillamine in pharmaceutical products by complexation with iron(III) in acidic media

A simple, robust and sensitive sequential injection spectrophotometric method for the assay of penicillamine (PA) in pharmaceutical formulations is developed. The method was based on the complex formation when PA is reacted with iron(III) solution in hydrochloric acid media. The deep blue colored PA-iron(III) complex produced is monitored at a maximum wavelength of 600 nm. A five level orthogonal array design coupled to genetic algorithm was employed to obtain the optimum experimental conditions for the determination of PA using peak absorbance as the measure of the system's performance criterion. A linear dynamic range for the determination of PA of 25-300 ppm was obtained with a sampling frequency of 50 h⁻¹ and a relative standard deviation of less than 0.98%. The method was successfully applied to the determination of PA in pharmaceutical formulations.     

Fractional factorial design based microwave‐assisted extraction for the determination of organophosphorus and organochlorine residues in tobacco by using gas chromatography—mass spectrometry

Sample preparation is often the main bottleneck in analyzing biological samples. Particularly, effective evaluation of sample preparation conditions usually involves multiple factors and tedious and time‐consuming experiments. In this study, fractional factorial design, specifically orthogonal array testing, was employed to screen and optimize multiple extraction parameters in concise but representative experiments. An efficient and sensitive method was developed to determine organophosphorus and organochlorine pesticide residues in tobacco, via microwave‐assisted extraction and gas chromatography coupled with mass spectrometry detection. With orthogonal array design, screening, and optimization tests were subsequently conducted to determine the range, impact rank, and possible interactions of extraction temperature, time, microwave power, additive salt, and additive water. Orthogonal array testing selectively reduces the size and cost of experiments and meanwhile provides more information compared to the traditional experimental design that optimizes one factor at a time. A good linear range (0.02–2.00 μg/mL), limits of detection (0.001–0.098 μg/mL), and recovery rates (70.4–107.1%) were demonstrated by spiking known concentrations of multiple pesticide standards in tobacco samples. The established method was then successfully applied to the determination of multipesticide residues in raw tobacco leaves and commercial cigarettes.     

Flow injection kinetic spectrofluorimetric determination of trace amounts of osmium

A flow injection (FI) kinetic spectrofluorimetric method is described for the determination of osmium(IV) and the possible mechanism of catalytic reaction is discussed. The method is based on the fluorescence enhancing reaction of o-vanillin furfuralhydrazone (OVFH) with potassium bromate, which is catalyzed by Os(IV) in water medium at pH 6.10 and 45 degrees C. OVFH is newly synthesized and its ionization, IR and elemental analysis are established. Under these experimental conditions, the oxidized product of OVFH has excitation and emission maxima at 337 and 490 nm, respectively. The linear range of this method is 0-600 ng ml(-1) with the R.S.D. of 1.2%. The detection limit is 1.0 ng ml(-1) of Os(IV). A high analysis rate of 24 samples h(-1) is obtained by the FI method. The proposed method is applied successfully to determine Os(IV) in synthetic mixture and mineral samples, and the results are well consistent with the standard values.     

Sequential optimization of a flow injection spectrophotometric method for the assay of chlorpromazine in pharmaceutical preparations

A new simple flow injection spectrophotometric method for the assay of chlorpromazine using cerium(IV) in sulfuric acid media was developed. The oxidized form of the drug was monitored at the maximum absorbance of 526 nm. The optimum conditions were 0.035M sulfuric acid, 3.80 x 10(-3)M cerium(IV), flow rate 4.85 ml/min, coil length 45 cm and sample size 110 mm(3). Optimization was carried out by the modified simplex method. Response surface methodology was employed to investigate the ruggedness of the method. A sampling frequency of 120 hr(-1) was attained. Relative standard deviations for standard sample were usually less than 0.75. The method was applied to the determination of chlorpromazine in proprietary drugs and results were statistically compared with the official British Pharmacopoeia (BP) method.     

Separation of some platinum metal 8-hydroxyquinolinates by normal phase high-performance liquid chromatography

The method of normal phase high-performance liquid chromatography has been applied to the separation and determination of Pd(II), Pt(II), Rh(III), Ir(IV), Ru(III) and Os(IV) as chelates with 8-hydroxyquinoline on a 62 x 2 mm column packed with Silasorb 600 5 mu silica gel by elution with methylene chloride-isopropyl alcohol mixture (97:3 v/v). The detection limits (ng per 5 mul), were Pd 0.3, Pt 1.0, Rh 1.0, Ir 5.0, Ru 1.5, Os 25. The separation time was 12 min at a flow-rate of 0.1 ml/min.     

Ultrasound-assisted emulsification microextraction coupled with gas chromatography–mass spectrometry using the Taguchi design method for bisphenol migration studies from thermal printer paper, toys and baby utensils

The optimization of a clean procedure based on ultrasound-assisted emulsification liquid-liquid microextraction for the sensitive determination of four bisphenols is presented. The miniaturized technique was coupled with gas chromatography-mass spectrometry after derivatization by in situ acetylation. The Taguchi experimental method, an orthogonal array design, was applied to find the optimal combination of seven factors (each factor at three levels) influencing the emulsification, extraction and collection efficiency, namely acetic anhydride volume, sodium phosphate concentration, carbon tetrachloride volume, aqueous sample volume, sodium chloride concentration and ultrasound power and application time. A second factorial design was applied with four factors and five levels for each factor, 25 experiments being performed in this instance. The matrix effect was evaluated, and it was concluded that sample quantification can be done by calibration with aqueous standards. The detection limits ranged from 0.01 to 0.03 ng mL(-1) depending on the compound. The environmentally friendly sample pretreatment procedure was applied to study the migration of the bisphenols from different types of samples: thermal printer paper, compact discs, digital versatile discs, small tight-fitting waistcoats, baby's bottles, baby bottle nipples of different materials and children's toys.     

Computer-assisted optimization of HPLC with post-column reaction for the determination of amino-acids

Computer-assisted optimization of a high-performance liquid chromatograph and associated post-column reactor is reported for the determination of six amino-acids. First six, then seven, experimental variables were considered. Non-standard experimental conditions were found which gave significantly improved colour development in the ninhydrin reaction. The composite modified simplex method for experimental optimization and a novel system-response function facilitated rapid and simultaneous improvement of separation, sensitivity and analysis time. The approach described is directly applicable to many similar systems.     

An Improved HPLC Method for Simultaneous Analysis of Losartan Potassium and Hydrochlorothiazide with the Aid of a Chemometric Protocol

An experimental design method was used for fast, simple, and accurate high-performance-pressure liquid chromatograpy (HPLC) determination of losartan and hydrochlorothiazide in combined dosage forms. This method avoids the disadvantages of the traditional analytical approach, which is time-consuming, involves a large number of runs, and does not allow the determination of multiple interacting parameters. On the basis of preliminary experiments, three independent variables (methanol content, pH value of the mobile phase, and flow rate) were selected as input, and as dependent variables, five responses (retention time of hydrochlorothiazide, retention time of losartan, asymmetry of hydrochlorothiazide peak, asymmetry of losartan peak, and resolution) were chosen. A full 2³ factorial design was used to determine which factors had an effect on the studied response. Afterwards, experimental design was used to optimize these influencing parameters in the previously selected experimental domain. After optimizing the experimental conditions, a separation was conducted on a Zorbax C₈ (150 mm × 4.6 mm, 5 μm particle size) column with a mobile phase consisting of methanol–acetonitrile–acetate buffer 45:20:35 v/v/v, pH 4.8 with flow rate of 0.82 mL min^?1 and column temperature of 25 °C. The developed method was successfully applied to simultaneous separation of these active drug compounds in their commercial pharmaceutical dosage forms.     

Application of artificial neural networks in multifactor optimization of an on-line microwave FIA system for catalytic kinetic determination of ruthenium (III)

A methodology based on the coupling of experimental design and artificial neural networks (ANNs) is proposed in the optimization of a flow injection system for the spectrophotometric determination of Ru (III) with m-acetylchlorophosphonazo (CPA-mA), which has been for the first time used for the optimization of high-performance capillary zone electrophoresis (J. Chromatogr. A 793 (1998) 317). And since it has been applied in many other regions like micellar electrokinetic chromatography, ion-interaction chromatography, HPLC, etc. (J. Chromatogr. A 850 (1999) 345; J. Chromatogr. A 799 (1998) 35; J. Chromatogr. A 799 (1998) 47). An orthogonal design is utilized to design the experimental protocol, in which five variables are varied simultaneously (Anal. Chim. Acta 360 (1998) 227). Feedforward-type neural networks with extended delta-bar-delta (EDBD) algorithm are applied to model the system, and the optimization of the experimental conditions is carried out in the neural network with 5-5-1 structure, which have been confirmed to be able to provide the maximum performance. In contrast to traditional methods, the use of this methodology has advantages in terms of a reduction in analysis time and an improvement in the ability of optimization. Under the optimum experimental conditions, Ru (III) can be determined in the range 0.040-0.60 mug ml(-1) with detection limit of 0.03 mug ml(-1) and the sampling frequency of 34 h(-1). The method has been applied to the determination of Ru (III) in refined ore as well as in secondary alloy and provided satisfactory results.     

Simultaneous analysis of irbesartan and hydrochlorothiazide: an improved HPLC method with the aid of a chemometric protocol

Experimental design method was used for HPLC determination of irbesartan and hydrochlorothiazide in combined dosage forms. The traditional approach for optimization of experiments is time-consuming, involves a large number of runs and does not allow establishing the multiple interacting parameters. The main advantages of the experimental design method include the simultaneous screening of a larger number of factors affecting response and the estimation of possible interactions. On the basis of preliminary experiments, three factors-independent variables were selected as inputs (methanol content, pH of the mobile phase and temperature) and as dependent variables, five responses (resolution, symmetry of irbesartan peak, symmetry of hydrochlorothiazide peak, retention factor of irbesartan and retention factor of hydrochlorothiazide) were chosen. A full 23 factorial design, where factors were examined at two different levels ("low" and "high") was used to determine which factors had an effect on the studied response. Afterwards, experimental design was used to optimize these influent parameters in the previously selected experimental domain. The novelty of our method lies in the optimization step accomplished by Derringer's desirability function. After optimizing the experimental conditions a separation was conducted on a Supelcosil C(18) (150 mm × 4.6 mm, 5 mm particle size) column with a mobile phase consisting of methanol-tetrahydrofuran-acetate buffer 47:10:43 v/v/v, pH 6.5 and a column temperature of 25 °C. The developed method was successfully applied to the simultaneous separation of these drug-active compounds in their commercial pharmaceutical dosage forms.