Ricardo Erthal Santelli

Response surface methodology (RSM) as a tool for optimization in analytical chemistry

A review about the application of response surface methodology (RSM) in the optimization of analytical methods is presented. The theoretical principles of RSM and steps for its application are described to introduce readers to this multivariate statistical technique. Symmetrical experimental designs (three-level factorial, Box-Behnken, central composite, and Doehlert designs) are compared in terms of characteristics and efficiency. Furthermore, recent references of their uses in analytical chemistry are presented. Multiple response optimization applying desirability functions in RSM and the use of artificial neural networks for modeling are also discussed.

Multivariate technique for optimization of digestion procedure by focussed microwave system for determination of Mn, Zn and Fe in food samples using FAAS

This article describes the development by response surface methodology (RSM) of a procedure for iron, zinc and manganese determination by flame atomic absorption spectrometry (FAAS) in food samples after digestion employing a focussed microwave system. A Doehlert matrix was used to find optimal conditions for the procedure through response surface study. Three variables (irradiation power and time and composition of oxidant solution-HNO(3)+H(2)O(2)) were regarded as factors in the optimization study. The working conditions were established as a compromise between optimum values found for each analyte taking into consideration the robustness of the procedure. These values were 12min, 260W and 42% (v/v) for irradiation time, irradiation power and percent of H(2)O(2) in solution, respectively. The accuracy of the optimized procedure was evaluated by analysis of certified reference materials and by comparison with a well-established closed vessel microwave dissolution methodology.

Flow injection determination of cobalt after its sorption onto polyurethane foam loaded with 2-(2-thiazolylazo)-p-cresol (TAC)

This paper reports the development of a new methodology for determination of cobalt in water samples by using a flow injection system with loaded PUF as solid phase to preconcentrate analytes. Procedure is based on on-line retention of Co(III) ions (generated in alkaline medium by Co(II) oxidation) in a minicolumn packed with a polyether type polyurethane foam loaded with TAC (2-(2-thiazolylazo)-p-cresol) and elution with 2 mol l(-1) HCl directly to the flame atomic absorption spectrometer nebulizer. Several chemical and flow variables that could affect the performance of this system were investigated as well as the possible interferents. For 2 min of preconcentration time (10.0 ml of sample volume) the system achieved a detection limit 3.2 mug l(-1), a R.S.D. 5% at 20 mug l(-1) and an analytical throughput 24 h(-1). Whereas for 3 min of preconcentration time (15.0 ml of sample volume) a detection limit 2.4 mug l(-1), a R.S.D. under 8% at 10 mug l(-1) and a sampling frequency 17 h(-1) were reported.

Especiação de Arsênio - uma revisão

This paper provides a review on separation methods and analytical techniques for the determination of several species of organic and inorganic arsenic in different matrices. Arsenic is an element whose speciation is of particular interest due to the great variation of toxicity levels exhibited for its different chemical forms. Arsenic (III) and As (V) are the most toxic species while organic compounds such as arsenobetaine (AsB), produced by methylation of inorganics species (carcinogenics) are relatively less toxic, hence the great importance of arsenic speciation in the determination of the degree of contamination of an environmental or biological system.

Determination of cadmium by FAAS after on-line enrichment using a mini column packed with Amberlite XAD-2 loaded with TAM

A procedure for determination of trace amounts of cadmium with on-line preconcentration has been proposed. It is based on chemical sorption of cadmium(II) ions onto a minicolumn packed with Amberlite XAD-2 resin loaded with TAM reagent. After being preconcentrated, cadmium was eluted by 0.50 mol l−1 hydrochloric acid solution and straight determined on-line by flame atomic absorption spectrometry. A time-based technique was used. Chemical and flow variables as well as concomitant ions were studied in the developed procedure. Detection limit (3σ, n=22) was 1.2 μg l−1 for the analytical curve within the range of 0–200.0 μg l−1. An enrichment factor of 108 and a retention efficiency of 75.6% were achieved for a sample volume of 5.2 ml (1 min preconcentration time). The precision of the continuous preconcentration method, calculated as the relative standard deviation in sample solutions containing 10 μg l−1 of cadmium was 4 and 9%, regarding repeatability and reproducibility, respectively. The selectivity of the proposed procedure was also evaluated. Results showed that iron(III), zinc(II), nickel(II), manganese(II), aluminum(III), copper(II), lead(II), cobalt(II), chromium(VI) (200 μg l−1 concentration) did not interfere during cadmium determination (10.0 μg l−1concentration). Achieved analytical results for rice flour (NIES 10c) and lobster hepatopancreas (TORT-1) standard reference materials were in good agreement with the certified values. A high sample throughput (40 samples h−1), preconcentration factor and simplicity are the main advantages in this analytical procedure.

An automated on-line flow system for the pre-concentration and determination of lead by flame atomic absorption spectrometry

Abstract The use of Amberlite XAD-2 modified by 2-(2-benzothiazolylazo)-2- p -cresol (BTAC) as a sorbent in an on-line pre-concentration system for lead determination has been proposed. The procedure is based on the sorption of lead(II) ions onto a minicolumn packed with modified Amberlite XAD-2, followed by elution with 0.10 mol l −1 hydrochloric acid and determination by flame atomic absorption spectrometry. The on-line flow system uses four three-way solenoid valves and is electronically controlled in a time-based mode. Chemical and flow variables were optimized. The results demonstrated that sample solutions containing lead(II) in the concentration range from 3.7 to 300.0 μg l −1 in a solution of pH between 6.5 and 8.5 could be determined, using a pre-concentration time of 2 min. The enrichment factor was 27 for a sample volume of 4.50 ml. The limit of detection was 3.7 μg l −1 . The relative standard deviations (R.S.D.) were in the range of 4.4–2.3% for lead concentrations from 50.0 to 300.0 μg l −1 , respectively. The method was tolerant to other ions usually present in biological samples. Good accuracy was assured by the analysis of biological reference materials.

Application of polyurethane foam loaded with BTAC in an on-line preconcentration system: cadmium determination by FAAS

Abstract In the present paper, the use of polyurethane foam modified by 2-(2-benzothiazolylazo)-2- p -cresol (BTAC) as a sorbent in an on-line preconcentration system to determine cadmium trace levels by FAAS is proposed. The procedure was based on the chemical sorption of cadmium (II) ions onto a minicolumn packed with polyurethane foam, followed by 0.10 mol l −1 hydrochloric acid elution and direct determination by Flame Atomic Absorption Spectrometry. The flow system was operated in a time-based mode. Chemical and flow variables were studied. Results demonstrated that sample solutions containing cadmium(II) in the range of concentration from 0.91 to 30.00 μg l −1 , pH between 6.50 and 9.25 could be determinated by this procedure, in a preconcentration time of 1 min. Flow rates in preconcentration and elution steps were 7.00 and 4.00 ml min −1 , respectively. The precision of the preconcentration procedure (evaluated as standard deviation of solutions containing 1.0–30.0 μg l −1 of cadmium) varied in the range from 5 to 1%. The preconcentration factor, calculated as the ratio of the linear section of the slopes of the analytical curves before and after preconcentration, was 41, for a volume sample of 7.00 ml. The detection limit was 0.27 μg l −1 for a preconcentration time of 1 min. The proposed procedure was applied for determination of cadmium in biological reference materials. Achieved results demonstrated that the procedure can be applied for analysis of biological materials with satisfactory accuracy.

Lead preconcentration onto C-18 minicolumn in continuous flow and its determination in biological and vegetable samples by flame atomic absorption spectrometry

A procedure for the preconcentration and determination of lead in vegetable and biological samples was developed in the continuous mode coupled to a flame atomic absorption spectrometer. Lead is quantitatively preconcentrated in acetic buffer as its diethyldithiocarbamate chelate onto a C-18 minicolumn, placed in the loop of a proportional injector, eluted by a stream of methyl isobutyl ketone and introduced directly into the nebuliser. A detection limit of 3 microg 1(-1) is obtained using a time-based technique for 2 min preconcentration and an RSD of 3.8% was readily achieved for three measurements of 25 microg Pb 1(-1). The sample throughput is 24 h(-1). Using preconcentration times of 10 min an enrichment factor of 189 can be obtained. The continuous flow system was used for some reference sample analysis and the obtained results reveal that the methodology can be easily applied for vegetable and biological sample analysis.

Regional geochemical baselines for sedimentary metals of the tropical São Francisco estuary, NE-Brazil

River catchments of the humid tropics deliver a large amount of the world’s particulate suspended matter and associated elements to the coastal zone (Hay, 1998; Meybeck, 1993). The estuaries and mangrove habitats set along this transport pathway transform, retain and accumulate a fraction of the river-borne particulates and metals in their sediments (Lee, 1995; Jennerjahn and Ittekkot, 2002; Machado and Lacerda, 2004). The metals are preferentially buried with fine-grained sediments and also affected by the mineralogy and content of organic matter (Hornberger et al., 1999). Many metal accumulation studies in coastal systems focused on the establishment of geochemical baselines for the evaluation of the degree of natural and/or anthropogenic metal loadings in the system. The tropical and sub-tropical coastal zone of Brazil has been subject to manifold metal contamination studies of its embayments, estuaries, coastal lagoons and mangrove habitats embedded in these systems affected by a varying degree of multiple human impacts, such as urbanization, industrialization, deforestation, land erosion and agricultural practices (Patchineelam et al., 1988; Lacerda et al., 1992, 1999, 2006; Marins et al., 2004). However, consistent geochemical baselines are still relatively scant and in practice may also only be established on a regional basis, as the grain size, mineralogical and chemical composition of suspended matter of Brazils tropical rivers varies greatly in accor-

On-line redox speciation analysis of antimony using l-proline immobilized on controlled pore glass and hydride generation inductively coupled plasma optical emission spectrometry for detection.

L-proline was immobilized on controlled pore glass to study the ability of this material for the separation and preconcentration of Sb(III) and Sb(V). The substrate was packed in a minicolumn and incorporated in a flow injection system. The effluents of the on-line solid phase extraction (before and after elution) were directly coupled to the hydride generation inductively coupled plasma optical emission spectrometry system. The effect of pH, sample (and eluent) volume, flow rates of sample loading and elution on separation of Sb(III) e Sb(V) were evaluated. Our experiments demonstrated that Sb(V) was not retained and it was selectively determined during the loading step, while retained Sb(III) was determined after elution. The proposed system was also used for the selective preconcentration of Sb(III). In this case, a preconcentration factor of 11 and a limit of detection of 90 ng L(-1) for Sb(III) were achieved when 8 mL of sample were loaded into the column. The speciation analysis of inorganic Sb in river water and effluent samples was performed using the proposed method. The values obtained for total Sb (obtained by sum of Sb(III) and Sb(V)) were in good agreement with expected values. Recoveries of Sb(III) and Sb(V) in the river water Standard Reference Material 1640 (from National Institute of Standard and Technology) and spiked river waters were between 83 and 111%.