Super-modified Simplex Method Research Articles

Carbon dioxide spectrophotometric determination in whole roasted coffee beans using a total analysis system after super-modified simplex optimization

In this work an automated methodology for the spectrophotometric determination of carbon dioxide in whole roasted coffee beans was developed. The analytical flow system was based on a reaction vessel featuring a lab-made gas diffusion flow cell. The coffee beans, without any pre-treatment, were poured in a vessel into which an acidic solution was added to promote carbon dioxide evolution from the sample. By pervaporation, the gas was thereafter trapped in a gas diffusion flow cell containing an acceptor solution which was afterwards analyzed by spectrophotometry. To enhance the sensitivity of the methodology, an experimental design based on super-modified simplex method was carried out to adjust the chemical composition of the acceptor solution. The developed methodology showed to be suitable to determine carbon dioxide in roasted coffee samples, and present as main advantages a higher determination rate (ca. 7 h−1) and reduced labor comparing with usually followed methodologies. Under the selected experimental conditions, the minimum quantity of carbon dioxide detected was of 4.62 × 10−7 mol. The results obtained by the developed methodology were correlated with those provided by the Hinman methodology.

APPLICATION OF THE MULTIRESPONSE OPTIMISATION SIMPLEX METHOD TO THE BIODIESEL - B100 OBTAINING PROCESS

<p>O processo de obtenção de biodiesel B100, a partir da transesterificação em meio básico, de uma mistura de óleo vegetal e gordura animal foi otimizado utilizando o método simplex supermodificado. Para otimização simultânea foram usados como respostas o rendimento, custo, estabilidade oxidativa e ponto de entupimento de filtro a frio (CFPP), e os limites foram estabelecidos de acordo com os dados experimentais e os parâmetros de conformidade estabelecidos pela legislação. A otimização multirresposta utilizando as equações preditivas, obtidas a partir do delineamento simplex-centroide acopladas às funções de desejabilidade, apresentou uma formulação ótima contendo 38,84% de óleo de soja, 21,90 % de sebo bovino e 39,25 % de gordura de ave com rendimento de 94,94 %, estabilidade oxidativa a 110 ºC de 8,99 horas, CFPP de 2,83 ºC e custo de US$ 864,60. A validação mostrou não haver diferença significativa entre os valores preditos e os valores experimentais. O delineamento de mistura e a otimização simplex-centroide se mostraram metodologias eficazes na obtenção de biodiesel B100, usando uma mistura de diferentes matérias-primas.</p>

Simultaneous micellar liquid chromatographic analysis of seven water-soluble vitamins: optimization using super-modified simplex

A super-modified simplex (SMS) method has been used to optimize the mobile phase used for separation of seven water-soluble vitamins in multivitamin tablets by gradient micellar liquid chromatography (MLC) with ultraviolet (UV) detection at 254, 295, and 361 nm. Effect of column temperature and addition of organic modifier to the mobile phase on separation efficiency were investigated: the appropriate conditions used were a temperature of 35 degrees C and 1-butanol modifier. The sodium dodecyl sulfate (SDS) concentration, pH, and 1-butanol% in the mobile phase were chosen for simultaneous optimization using the SMS method. The optimum mobile phase was found to be 16 mmol L(-1) (mM) SDS, 0.02 M phosphate buffer, pH 3.6, and a gradient of 3.5-10% (v/v) butanol. The total analysis time for vitamins was 75 min. The analytical parameters including linearity ( r>0.9970), limit of detection (0.12-50 micro g mL(-1)), precision of method (relative standard deviation (RSD) <8.90%), and accuracy obtained by the recovery assay (88-103%) support the usefulness of the proposed method for the determination of the water-soluble vitamins.

On-line preconcentration and simultaneous determination of heavy metal ions by inductively coupled plasma-atomic emission spectrometry

A flow injection analysis system for on-line preconcentration and simultaneous determination of Bi 3+, Cd 2+, Co 2+, Cu 2+, Fe 3+, Ni 2+, Pb 2+ and Zn 2+ in aqueous samples by inductively coupled plasma (ICP)-atomic emission spectrometry with a charge coupled detector is described. The preconcentration of analytes is accomplished by retention of their chelates with sodium diethyldithiocarbamate in aqueous solution on a solid phase containing octadecyl silica in a minicolumn. Methanol, as eluent, is introduced into the conventional nebulizer of the ICP instrument. The effects of different parameters, including preconcentration flow rate (equal to sample flow rate (SR)), eluent flow rate (ER), weight of solid phase (W) and eluent loop volume (EV), were optimized by the super-modified simplex method. The optimum conditions were evaluated to be SR 7.2 ml min −1, ER 3.5 ml min −1, W of 100 mg and EV of 0.8 ml. An enrichment factor of 312.5 for each analyte was obtained. The detection limits of the proposed method for Bi 3+, Cd 2+, Co 2+, Cu 2+, Fe 3+, Ni 2+, Pb 2+ and Zn 2+ were evaluated as 1.3, 1.0, 0.8, 0.3, 14.7, 0.5, 5.5 and 0.1 ng l −1, respectively. The effect of several metal ions on percent recovery was also studied. The method was applied to the recovery of these heavy metals from real matrices and to the simultaneous determination of these cations in different water samples.

Método simplex supermodificado como estratégia de otimização para respostas combinadas em sistemas alimentares

O presente trabalho teve como objetivo combinar modelagem pela superficie de resposta com otimizacao simplex supermodificado, para tratamento de casos de interesse na ciencia e tecnologia de alimentos, com o emprego da funcao de Derringer & Suich para respostas combinadas. Um programa para microinformatica, denominado MULTIPLEX, foi desenvolvido e testado na otimizacao multirresposta de tres sistemas alimentares selecionados na literatura especializada: 1) inativacao da lipoxigenase e lipase preservando-se a atividade da fitase durante o processamento hidrotermico da cevada; 2) desidratacao instantânea de maca por expansao; 3) extracao da proteina da linhaca com hexametafosfato. Uma analise estatistica rigorosa foi realizada para testar a capacidade preditiva dos modelos. O metodo simplex supermodificado, com inicializacao automatica, foi o instrumento para a solucao numerica da funcao de Derringer & Suich para respostas combinadas. O programa desenvolvido mostrou ser eficiente e confiavel para a otimizacao de multirrespostas, sendo executavel em microcomputador que disponha de processador 486 e ambiente MS-DOS.

Determination of the Accurate Values of the Rate Constant and Thermodynamic Parameters for the Rotation About the C(sp2)-C(aryl) Bond. 3-Substituted N,N,2,4,6-Pentamethylbenzamides

Three programs for the 1H NMR line shape analysis of systems with unequally populated sites have been tested in order to get highly accurate rate constants of the hindered rotation about a single bond using four published criteria. The programs differ in the number of optimized parameters. As test compounds, 3-(adamantan-1-carbonyl)-N,N,2,4,6-pentamethylbenzamide (1) and 3-(2-dimethylpropanoyl)-N,N,2,4,6-pentamethylbenzamide (2) were prepared. It was found that a supermodified simplex method with only six parameters optimized in one step gives the most accurate values of the rate constants. Consequently, the calculated thermodynamic parameters Ea, ∆H≠ and ∆S≠ lie in relatively narrow confidence intervals.

Chemometrical optimization FIA of perphenazine assay

A flow injection method for the assay of perphenazine using cerium(IV) as oxidant in a sulphuric acid media was adopted. Different chemometric techniques, considered the main objective of this work, were utilised to optimise sensitivity and sample throughput as a function of five experimental variables. The optimum conditions obtained by the super modified simplex method were, 0.170 M sulphuric acid, 2.13 mM cerium(IV), 2.56 ml min −1 flow rate, 52 cm coil length, and 136 μl sample loop size. A central composite design was successfully employed, characterising the relation between these variables and the response surface, and hence validating the optimum conditions obtained by the simplex method. Regression analysis of the data from the experimental design, demonstration that a second order polynomial model is an adequate description of the surface over the factor limits studied. Further analysis of the response surface revealed the presence of a broad maximum around the simplex method optimum. A linear calibration curve in the range 50–500 ppm together with a sampling frequency of at least 120 s h −1 and a relative standard deviation of less than 0.8% were obtained for the determination of perphenazine in its pure analytical grade. Results of the perphenazine assay in pharmaceutical preparations indicates that the method does not suffer interference from excipients rendering the method suitable for the assay of perphenazine in drug formulations.

Determination of the Accurate Values of the Rate Constant and Thermodynamic Parameters for the Rotation About the C(sp2)-C(aryl) Bond; Adamantan-1-yl 3-Bromo-2,4,6-trimethylphenyl Ketone

Four programs for the 1H NMR line shape analysis: two commercial - Winkubo (Bruker) and DNMR5 (QCPE 165) and two written in our laboratory - Newton (in Microsoft Excel) and Simtex (in Matlab) have been tested in order to get highly accurate rate constants of the hindered rotation about a single bond. For this purpose four testing criteria were used, two of them were also developed by us. As supplementary determinations the rate constants obtained for the coalescence temperature and for the thermal racemization of chromatographically separated enantiomers were used which fitted well the temperature dependence of the rate constants determined by the line shape analysis. As a test compound adamantan-1-yl 3-bromo-2,4,6-trimethylphenyl ketone was prepared and studied. It was shown that supermodified simplex method used in our algorithm (Simtex), though time consuming, gives the most accurate values of the rate constants and consequently the calculated thermodynamic parameters Ea, ∆H≠, and ∆S≠ lay in relatively narrow confidence intervals.

Free cholesterol fiber-optic biosensor for serum samples with simplex optimization

An optical fiber biosensor for free cholesterol monitoring in serum samples is described. Silicone-entrapped tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) complex, the luminescence of which is sensitive to oxygen changes, is used as an optical transducer of the oxidation of cholesterol by cholesterol oxidase. The biocatalyst is entrapped in a graphite powder layer deposited onto the dyed silicone film. Optimization of some interdependent chemical variables which affect the performance of the biosensor has been achieved by application of a super-modified simplex method. The dynamic range of the biosensing membranes is found to be 0·15–3·0 mM of free cholesterol. Studies of the reproducibility, stability and interferences of the device, as well as the application of the sensor to measurements in serum samples, are reported. Simplex optimization has proven to be a very useful tool in the search for the optimal conditions for performing analyses with the optical fiber biosensor.

Chemometric optimization and flow injection method for the determination of norfloxacin in drug formulations

A flow injection spectrophotometric method for the determination of the antibiotic norfloxacin in drug formulations in the range 50–450 ppm was developed. Iron(III) was employed to produce a coloured complex absorbing at 430 nm in sulfuric acid medium. A factorial design program was utilized to establish the highly interacting factors that must be optimized. Optimization was carried out by the super modified simplex method. The optimum conditions were 0.043 mol dm–3 sulfuric acid, 0.0271 mol dm–3 iron(III), flow rate 5.33 cm3 min–1, sample size 210 mm3 and coil length 45 cm. A sampling frequency of 140 h–1 was attained.

Optimization of an ion-exchange high-performance liquid chromatographic method for the determination of carboxylic acids, sugars, glycerol and ethanol in wines

Optimization of ion-exchange high-performance liquid chromatography with refractive index detection of major carboxylic acids, sugars, glycerol and ethanol in wines was carried out by using a super-modified simplex method and a modelling response surface method. A modification of the CRF criterion (chromatographic response function) for selectivity optimization was used, including different weighting factors for each pair of peaks (VCP criterion; variable coefficient parameters).