Walter Nei Lopes dos Santos

Separation and preconcentration procedures for the determination of lead using spectrometric techniques: A review

Lead is recognized worldwide as a poisonous metal. Thus, the determination of this element is often required in environmental, biological, food and geological samples. However, these analyses are difficult because such samples contain relatively low concentrations of lead, which fall below the detection limit of conventional analytical techniques such as flame atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry. Several preconcentration procedures to determine lead have therefore been devised, involving separation techniques such as liquid-liquid extraction, solid phase extraction, coprecipitation and cloud point extraction. Citing 160 references, this paper offers a critical review of preconcentration procedures for determining lead using spectroanalytical techniques.

Current Status of Direct Solid Sampling for Electrothermal Atomic Absorption Spectrometry—A Critical Review of the Development between 1995 and 2005

Abstract The literature about direct solid sampling (SS) and slurry sampling atomic absorption spectrometry (AAS) over the past decade has been surveyed critically. It became apparent that a very significant change had occurred, particularly in the relation between the two major techniques used for that purpose. In the 1990s, slurry sampling was typically considered the technique of choice, combining the significant advantages of the solid and the liquid sampling methods, at least in part because of the availability of a commercial accessory for automatic slurry sampling. The situation is completely inverted now, as the above accessory has been discontinued and rugged and reliable accessories for direct SS became available. Direct SS electrothermal (ET) AAS has been shown to provide the best limits of detection because of the absence of any dilution and a minimal risk of contamination. Calibration against aqueous standards appears to be feasible after careful program optimization. The absence of any significant sample handling makes SS ET AAS ideally suited for fast screening analyses. The introduction of high‐resolution continuum source AAS appears to open additional attractive features for SS ET AAS because of the significantly simplified optimization of furnace programs and the visibility of the spectral environment, which makes it easy to avoid spectral interferences. New calibration strategies make a “dilution” of samples unnecessary, which used to be one of the major limitations of SS ET AAS. Finally, direct SS analysis is an important contribution to clean chemistry, as practically no reagents are used.

Uranium determination using atomic spectrometric techniques: an overview.

This review focuses on the determination of uranium using spectroanalytical techniques that are aimed at total determination such as flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ETAAS), inductively coupled plasma optical emission spectrometry (ICP-OES); and inductively coupled plasma mass spectrometry (ICP-MS) that also enables the determination of uranium isotopes. The advantages and shortcomings related to interferences, precision, accuracy, sample type and equipment employed in the analysis are taken into account, as well as the complexity and costs (i.e., acquisition, operation and maintenance) associated with each of the techniques. Strategies to improve their performance that employ separation and/or preconcentration steps are considered, with an emphasis given to solid-phase extraction because of its advantages compared to other preconcentration procedures.

Multi-element determination of Cu, Fe, Ni and Zn content in vegetable oils samples by high-resolution continuum source atomic absorption spectrometry and microemulsion sample preparation

The aim of this work was to evaluate the microemulsification as sample preparation procedure for determination of Cu, Fe, Ni and Zn in vegetable oils samples by High-Resolution Continuum Source Flame Atomic Absorption Spectrometry (HR-CS FAAS). Microemulsions were prepared by mixing samples with propan-1-ol and aqueous acid solution, which allowed the use of inorganic aqueous standards for the calibration. To a sample mass of 0.5g, 100μL of hydrochloric acid and propan-1-ol were added and the resulting mixture diluted to a final volume of 10mL. The sample was manually shaken resulting in a visually homogeneous system. The main lines were selected for all studied metals and the detection limits (3σ, n=10) were 0.12, 0.62, 0.58 and 0.12mgkg(-1) for Cu, Fe, Ni and Zn, respectively. The relative standard deviation (RSD) ranged from 5% to 11 % in samples spiked with 0.25 and 1.5μgmL(-1) of each metal, respectively. Recoveries varied from 89% to 102%. The proposed method was applied to the determination of Cu, Fe, Ni and Zn in soybean, olive and sunflower oils.

Slurry Sampling—An Analytical Strategy for the Determination of Metals and Metalloids by Spectroanalytical Techniques

Abstract This article critically overviews the state-of-the-art of slurry sampling as an approach for the minimization of sample preparation prior to the determination of metals and metalloids in complex matrices by spectroanalytical techniques. Relevant factors involved in the optimization of slurry-based analytical procedures and the dependence of the quality of the results on the calibration method selected are discussed in detail. The advantages and limitations compared to solid sampling for the analysis of solid matrices are highlighted and discussed. Analytical applications of slurry sampling reported in the literature emphasizing publications between 2004 and 2009 are comprehensively compiled covering detection by flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ET-AAS), cold vapor atomic absorption spectrometry (CV-AAS), hydride generation atomic absorption spectrometry (HG-AAS), hydride generation atomic fluorescence spectrometry (HG-AFS), inductively coupled plasma optical emission spectrometry (ICP-OES), and inductively coupled plasma mass spectrometry (ICP-MS).

Application of three-variables Doehlert matrix for optimisation of an on-line pre-concentration system for zinc determination in natural water samples by flame atomic absorption spectrometry

Abstract This article describes an on-line pre-concentration system for zinc determination in environmental samples by flame atomic absorption spectrometry (FAAS). It was based on the sorption of zinc(II) ions in a minicolumn of polyurethane foam loaded with 4-(2-pyridylazo)-resorcinol (PAR). The optimisation step was carried out using two-level full factorial and a Doehlert design. Three variables (sampling flow rate, buffer concentration and pH) were regarded as factors in the optimisation. Results of the two-level full factorial design 23 for 8 runs (in duplicate) based on the Analysis of Variance (ANOVA) demonstrated that all the factors in the tested levels are statistically significant. Besides, the interaction (sampling flow rate×buffer concentration) was also statistically significant. A three-variables Doehlert design was applied in order to determine the best condition for pre-concentration and determination of zinc. The validation process was assessed as: parameters of the analytical curve, precision, effect of other ions in the proposed system, robustness test and accuracy. The proposed system allowed determination of zinc with detection limit (3σ/S) of 0.28 μg l−1, and a precision (reproducibility), calculated as relative standard deviation (R.S.D.) of 10.0 and 3.7% for zinc concentration of 1.0 and 5.0 μg l−1, respectively. The achieved pre-concentration factor was 91.23 and the sampling frequency was 48 samples per hour. The achieved recovery for zinc determination in presence of several cations demonstrated that this procedure could be applied for analysis of water samples. The accuracy was confirmed by analysis of three certified reference materials. This procedure was applied for zinc determination in several kinds of water samples including saline aqueous waste from oil Refinery.

Palladium as chemical modifier for the stabilization of volatile nickel and vanadium compounds in crude oil using graphite furnace atomic absorption spectrometry

It has been observed in previous work using high-resolution continuum-source atomic absorption spectrometry that up to 50% of the nickel and vanadium in crude oil, most likely non-polar nickel and vanadyl porphyrin complexes, was already lost at pyrolysis temperatures >400 °C, whereas the rest of the analyte was stable up to at least 1200 °C. In this work we were investigating the use of a chemical modifier in order to avoid these low-temperature losses and also to make possible a differential determination of the volatile analyte fractions. Oil-in-water emulsions, using Triton X-100 as surfactant, were used for easy sample handling. A mass of 20 μg of Pd, introduced into the graphite tube and thermally pretreated prior to the injection of the emulsion, was found to efficiently prevent any low-temperature losses of nickel and vanadium from crude oil samples up to pyrolysis temperatures of 1200 °C and 1450 °C, respectively. The best characteristic mass obtained was m0 = 16 pg for Ni and m0 = 33 pg for V. The limits of detection and quantification were 0.02 μg g−1 and 0.065 μg g−1, respectively, for Ni, and 0.06 μg g−1 and 0.17 μg g−1, respectively, for V in oil, based on an emulsion of 2 g of oil in 10 mL. The precision expressed as relative standard deviation (n = 9) for a crude oil containing about 5 μg g−1 Ni and 3 μg g−1 V was 2.0% and 3.1% for Ni and V, respectively. The accuracy of the procedure was verified by analyzing the certified reference material NIST SRM 1634c, trace metals in fuel oil, and the research material RM 8505, vanadium in crude oil.

Direct determination of iron and manganese in wine using the reference element technique and fast sequential multi-element flame atomic absorption spectrometry

A procedure is proposed for the direct determination of manganese and iron in wine employing fast sequential flame atomic absorption spectrometry and the reference element technique to correct for matrix effects. Cobalt, silver, nickel and indium have been tested as reference elements. The results demonstrated that cobalt and indium at a concentration of 2 and 10mgL(-1) were efficient for quantification of manganese and iron, respectively. Under these conditions, manganese and iron could be determined with quantification limits of 27 and 40microg L(-1), respectively. The proposed method was applied to the determination of manganese and iron in 16 wine samples. The content of manganese varied from 0.78 to 2.89mgL(-1) and that of iron from 0.88 to 9.22mgL(-1). The analytical results were compared with those obtained by inductively coupled plasma optical emission spectrometry after complete mineralization using acid digestion. The statistical comparison by a t-test (95% confidence level) showed no significant difference between the results.

Factorial Design and Doehlert Matrix in Optimization of Flow System for Preconcentration of Copper on Polyurethane Foam Loaded with 4‐(2‐Pyridylazo)‐resorcinol

Abstract 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 (23) 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 × 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 µg L−1 and precision (n = 8) as relative standard deviation (RSD) of 3.2 and 1.1 for copper solutions containing 10 and 30 µg L−1, respectively. Also, a satisfactory linear range (1.2–40 µg 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(II) 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) NaCl). 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%.

Mercury determination in petroleum products by electrothermal atomic absorption spectrometry after in situ preconcentration using multiple injections

A simple method for mercury determination in petroleum fractions (e.g. naphtha) using electrothermal atomic absorption spectrometry (ETAAS) associated with multiple injection technique for direct preconcentration in the graphite tube has been developed. Oil-in-water micro-emulsions (three-component solutions) were prepared using a mixture of sample, propan-1-ol and HNO3. No additional sample pretreatment was required. In the procedure, three successive 30 μL micro-emulsion aliquots are delivered to the graphite tube. The pyrolysis and atomization temperatures were set to 400 °C and 1400 °C, respectively. The calibration curves showed a linear response up to analyte concentrations of 150 μg L−1 with a correlation coefficient of 0.993. The precision calculated from fifteen consecutive measurements and defined as the coefficient of variation of solutions containing 5.0 and 30 μg L−1 of Hg were 6.4% and 4.7%, respectively. The limit of detection (LOD), defined as the Hg concentration that gives a response equivalent to three times the standard deviation (s) of the blank (n = 10), was found to be 0.78 μg L−1. The proposed procedure was used for mercury determination in naphtha feeds processed in Braskem S.A. (Salvador, Bahia, Brazil).