Roy E. Bruns

Flow injection systems with inductively-coupled argon plasma atomic emission spectrometry: Part 1. Fundamental Considerations

Abstract Flow injection systems with inductively-coupled argon plasma atomic emission spectromeiry are proposed. Effects of flow rates, injected volumes and mixing Coil lengths are investigated and conditions for the measurement of the flow injection transient signal are discussed. The peak profile measured with the spectrometer corresponds well with the estimate of the true sample zone distribution near the inlet of the spectrometer made by a zone-sampling process; thus the plasma is not a limiting factor in the proposed systems. For plant analysis, the system provides nearly zero sample dispersion and so the inherent sensitivity of the spectrometric method is preserved. The results obtained for 10 elements in the NBS Orchard Leaves reference material (SRM 1571) are in good agreement with the certified values. For determinations of calcium and magnesium in dolomitic limestones, cadmium is used as internal standard and so the merging zones configuration is employed. The proposed system provides medium sample dispersion and permits about 100 samples to be analysed per hour. Relative standard deviations of 1.34% and 1.23% were calculated for the calcium and magnesium data, respectively. The analytical results compare favorably with those obtained by normal i.c.p. spectrometry with pneumatic sample aspiration, after manual sample dilution.

SIMULATION OF AN INDUSTRIAL WASTEWATER TREATMENT PLANT USING ARTIFICIAL NEURAL NETWORKS AND PRINCIPAL COMPONENTS ANALYSIS

This work presents a way to predict the biochemical oxygen demand (BOD) of the output stream of the biological wastewater treatment plant at RIPASA S/A Celulose e Papel, one of the major pulp and paper plants in Brazil. The best prediction performance is achieved when the data are preprocessed using principal components analysis (PCA) before they are fed to a backpropagated neural network. The influence of input variables is analyzed and satisfactory prediction results are obtained for an optimized situation.

Use of multivariate statistical techniques to optimize the simultaneous separation of 13 phenolic compounds from extra-virgin olive oil by capillary electrophoresis.

Characterization of phenolic compounds in olive oil has not been achieved as yet, owing to the complexities of their chemical structures and analytical matrix. The aim of this work is to optimize and validate a method for simultaneous separation and quantification of 13 phenolic compounds from extra-virgin olive oil: tyrosol, hydroxytyrosol, oleuropein glycoside, ferrulic acid, p-coumaric acid, cinnamic acid, p-hydroxybenzoic acid, gallic acid, caffeic acid, luteolin, apigenin, vanillic acid and 3,4-dihydroxybenzoic acid. A statistical central composite design, response surface analysis and the simultaneous optimization method of Derringer and Suich were used to separate all the peaks. These multivariate procedures were efficient in determining the optimal separation condition, using five peak-pair resolutions and runtime as responses. The optimized method employed a fused-silica capillary of 50 μm i.d.× 60 cm effective length with extended light path, 50 mmol L(-1) boric acid electrolyte, 10.2 pH, 25°C, injection of 50 mbar for 25s with application of reverse voltage (-30 kV for 5s) before setting the running voltage (+30 kV) with detection at 210 nm and a run time of 12 min. Peak resolutions are found to be very sensitive to pH values outside the 10.15-10.25 range but acceptable electropherograms can be obtained for a wide range of boric acid concentrations within this pH interval.

Hidrocarbonetos policíclicos aromáticos como traçadores da queima de cana-de-açúcar: uma abordagem estatística

In this study atmospheric particulates of PAHs were measured in Araraquara, Piracicaba and Sao Paulo in July 2003 (sugarcane harvest season in Araraquara and Piracicaba) and in Araraquara in March of 2003. The results were normalized to the total PAH concentrations. Comparison among the sites and principal component analysis (PCA) were used to investigate possible tracers of emission. Fluoranthene and pyrene concentrations were higher in Piracicaba and Araraquara samples. These PAH were also responsible for the largest negative loadings on the second principal component and account for the negative scores and for the formation of the Araraquara and Piracicaba group.

Factorial design and response surface optimization of crude violacein for Chromobacterium violaceum production

Initially an eleven variable, sixteen assay 215−11 fractional factorial design, was used to determine the key factors in the production of violacein produced by Chromobacterium violaceum, CCT 3496. Subsequently five and three factor central composite designs were executed to determine response surfaces with the aim of optimizing cellular mass and crude violacein production. The 7.5 g l−1 dry cell mass and 0.17 g l−1 crude violacein productions obtained with our initial culture medium were increased to 21 g l−1 and 0.43 g l−1, respectively, for a medium investigated in the three factor design.

Simultaneous determination of first-line anti-tuberculosis drugs by capillary zone electrophoresis using direct UV detection.

An alternative methodology for simultaneous analysis of ethambutol, isoniazid, rifampicin and pyrazinamide in pharmaceutical formulations by capillary zone electrophoresis under UV direct detection with an analysis time of 8.0 min is proposed. Background running was based on the effective mobility curve of the analytes and an optimum separation condition was achieved using a 3(3) Box-Behnken design, with Brij 35, Cu(2+) and acetic acid/sodium acetate buffer as factors. An electrolyte consisting of 50.0 mmol L(-1) of acetic acid/sodium acetate buffer, 12.5 mmol L(-1) of CuSO(4), and standard and sample solutions prepared in 2.00 mmol L(-1) of Brij 35 and 12.5 mmol L(-1) of CuSO(4) were optimized. After evaluating validation parameters, the method was successfully applied to the analysis of samples in the form of tablets and sachets.

25 anos de quimiometria no Brasil

Chemometric activities in Brazil are described according to three phases: before the existence of microcomputers in the 1970s, through the initial stages of microcomputer use in the 1980s and during the years of extensive microcomputer applications of the ´90s and into this century. Pioneering activities in both the university and industry are emphasized. Active research areas in chemometrics are cited including experimental design, pattern recognition and classification, curve resolution for complex systems and multivariate calibration. New trends in chemometrics, especially higher order methods for treating data, are emphasized.

A fast procedure for standard additions in flow injection analysis

Abstract A method based on the concentration/time profile generated by the injection of a single standard solution is described. The method is applied to the determination of sodium, potassium and calcium by flame photometry. Calibration graph errors as high as 60% are reduced to 3% by using the standard addition method.

CNDO calculation of dipole moment derivatives and infrared intensities of formaldehyde

The complete neglect of differential overlap (CNDO) approximate wavefunctions for formaldehyde have been applied to the calculation of the derivatives of the dipole moment with respect to the symmetry coordinates (∂p/∂Sj). Agreement between the calculated derivatives and the experimental values given by Hisatsune and Eggers for the A1 symmetry species is exceptionally good, permitting an interpretation of the experimental results in terms of electronic distributions in the molecule. The agreement for the B1 and B2 symmetry species is also very good except for the asymmetric in‐plane CH bend. However, the theory successfully predicts that charge reorientation for this motion is quite different from that which occurs in the out‐of‐plane CH bend, so that these motions are represented by CH bond moments of opposite polarity. An analysis is given of the results in terms of derivatives with respect to internal coordinates (∂p/∂rk). Comparison of ∂p/∂rCO values from a series of X2CO molecules (and also with ∂p/∂...

Factorial design of electrolyte systems for the separation of fatty acids by capillary electrophoresis.

In this work, a capillary zone electrophoretic methodology using UV indirect detection (224 nm) for the analysis of fatty acids (FAs) in saponified oils is proposed. The electrolyte consisted of a 5 mmol l(-1) phosphate buffer, pH 7. containing 4 mmol l(-1) sodium dodecylbenzenesulfonate (SDBS) as chromophore, 4 mmol l(-1) dimethyl-beta-cyclodextrin and 45% acetonitrile (ACN). The composition of the electrolyte was optimized by a 2(3) factorial design with triplicate at the central point. The design established practical concentration boundaries for SDBS and ACN. In a defined concentration range of 2-4 l(-1), SDBS can certainly be used as a chromophore for indirect detection without imparting excessive baseline noise. For ACN, a suitable interval of 45-55% was found to enhance FAs solubilization without overflowing the system with bubble formation and current interruption. Additionally, the design revealed the importance of dimethyl-beta-cyclodextrin in the resolution of difficult pairs and its function as a solubilizing agent for long chain FAs. At the optimized conditions, nine FAs from C10 to C20, including mono- di- and tri-unsaturated C18 fatty acids were baseline separated in less than 10 min. The proposed method was applied to the separation of FAs in edible oils and polyunsaturated fatty acid enriched margarine. Additionally, spectral monitoring at 206 nm was used to confirm peak identity in the samples.