Factorial design and doehlert matrix in optimization of flow system for preconcentration of copper on polyurethane foam loaded with 4-(2-pyridylazo)-resorcinol

The present paper describes a flow preconcentration system for copper determination by flame atomic absorption spectrometry (FAAS) based on the sorption of Cu(II) ions onto a mini-column of polyurethane foam (PUF) loaded with a chromogenic reagent [4-(2-pyridylazo)resorcinol (PAR)]. The variables associated with flow preconcentration system performance, such as pH, buffer concentration (BC), and sampling flow rate (SF), were optimised using a full factorial (2 3) design plus a central point and Doehlert matrix. The results obtained, based on the Pareto chart and analysis of variance (ANOVA), demonstrated that pH and BC, as well as the interaction (pH x BC) are statistically significant at the 95% confidence level. By using 20 mL of sampling volume the proposed method, under conditions optimised by the Doehlert matrix (formation of Cu(II)-PAR (1: 2) complex at pH 6.4, 0.017 mol L-1 phosphate BC, and 10 mL min(-1) SF), allows to determine Cu(II) ions with a detection limit of 0.35 mug L-1 and precision (n = 8) as relative standard deviation (RSD) of 3.2 and 1.1 for copper solutions containing 10 and 30 mug L-1, respectively. Also, a satisfactory linear range (1.2-40 [mug L-1), an enrichment factor of 105 and a sample throughput of 28 hr(-1) were achieved. Interference studies showed that the PUF-PAR mini-column retains Cu(H) ions in the presence of several transition and alkali metals without presenting interferences. The method was applied for copper determination in water samples (mineral and tap water) and high salt aqueous samples (physiological serum containing 0.9% (m/v) NaCI). The validation of the method was checked by analysing the Cu(II) content in the samples, as well as from analyte addition. The recoveries ranged from 91.0% to 101.1%.3771437145

Mixture Design Optimization of an Analytical Procedure for Iron Extraction and Determination From Cassava Leaves by Slurry Sampling Flame Atomic Absorption Spectrometry

This paper applies statistical simplex-centroid design to mixture modeling for optimization of the liquid phase composition of cassava slurry leaves in the development of an analytical procedure for iron determination using flame atomic absorption spectrometry (FAAS). This procedure is based on a slurry formation from powdered cassava leaves and a liquid mixture composed of HNO3, HCl, and H2O2 after an ultrasonication process. A quadratic model fitted to the analytical response shows the existence of an experimental region, characterized by low proportions of H2O2, for which higher responses are obtained. The proposed procedure allows the determination of iron in the cassava leaves with a detection limit of 1.1 mu g g(-1). The precision expressed as relative standard deviation (%RSD, n = 10) was 1.5% for iron concentrations of 25 mu g g(-1). The developed procedure was validated by the comparison of results obtained from the application of the digestion procedure and the analysis of certified reference materials: Apple leaves (NIST 1515). Results found were in agreement with the certified values. The proposed method was applied for the determination of iron in four samples of cassava leaves acquired in markets of Feira de Santana City, Brazil. The concentration of iron found in the cassava leaves varied from 250.8 +/- 0.7 to 283.4 +/- 0.7 mu g g(-1).44638839

Automatic on-line pre-concentration system using a knotted reactor for the FAAS determination of lead in drinking water

An automatic on-line pre-concentration system is proposed for lead determination in drinking water using flame atomic absorption spectrometry (FAAS). Lead(II) ions are retained as the 1-(2-pyridylazo)-2-naphthol (PAN) complex in the walls of a knotted reactor, followed by an elution step using 0.50 mol L-1 hydrochloric acid solution. Optimisation involving the sampling flow rate, pH and buffer concentration factors was performed using a Box-Behnken design. Other factors were established considering results of previous experiments. T he procedure allows the determination of lead with a 0.43 mu g L-1 detection limit (3 sigma/S) and precisions (expressed as relative standard deviation) of 4.84% (N = 7) and 2.9% (N = 7) for lead concentrations of 5 and 25 mu g L-1, respectively. The accuracy was confirmed by the determination of lead in the NIST SRM 1643d trace elements in natural water standard reference material. The pre-concentration factor obtained is 26.5 and the sampling frequency is 48 h(-1). The recovery achieved for lead determination in the presence of several ions demonstrated that this procedure could be applied to the analysis of drinking water samples. The method was applied for lead determination in drinking water samples collected in Jequie City, Brazil. The lead concentration found in 25 samples were always lower than the permissible maximum levels stipulated by World Health Organization. (c) 2006 Elsevier B.V. All rights reserved.141354054