Laiana O.B. Silva

Determination of mercury in phosphate fertilizers by cold vapor atomic absorption spectrometry

In this paper, a method for the determination of mercury in phosphate fertilizers using slurry sampling and cold vapor atomic absorption spectrometry (CV QT AAS) is proposed. Because mercury (II) ions form strong complexes with phosphor compounds, the formation of metallic mercury vapor requires the presence of lanthanum chloride as a release agent. Thiourea increases the amount of mercury that is extracted from the solid sample to the liquid phase of the slurry. The method is established using two steps. First, the slurry is prepared using the sample, lanthanum chloride, hydrochloric acid solution and thiourea solution and is sonicated for 20 min. Afterward, mercury vapor is generated using an aliquot of the slurry in the presence of the hydrochloric acid solution and isoamylic alcohol with sodium tetrahydroborate solution as the reducing agent. The experimental conditions for slurry preparation were optimized using two-level full factorial design involving the factors: thiourea and lanthanum chloride concentrations and the duration of sonication. The method allows the determination of mercury by external calibration using aqueous standards with limits of detection and quantification of 2.4 and 8.2 μg kg(-1), respectively, and precision, expressed as relative standard deviation, of 6.36 and 5.81% for two phosphate fertilizer samples with mercury concentrations of 0.24 and 0.57 mg kg(-1), respectively. The accuracy was confirmed by the analysis of a certified reference material of phosphate fertilizer that was provided by the National Institute of Standards & Technology (NIST). The method was applied to determine mercury in six commercial samples of phosphate fertilizers. The mercury content varied from 33.97 to 209.28 μg kg(-1). These samples were also analyzed employing inductively coupled plasma mass spectrometry (ICP-MS). The ICP-MS results were consistent with the results from our proposed method.

Determination of cadmium in rice by electrothermal atomic absorption spectrometry using aluminum as permanent modifier

In this paper, the use of aluminum as a permanent modifier for the determination of cadmium in rice by electrothermal atomic absorption spectrometry (ETAAS) was investigated. The optimized experimental conditions, which employed a full two-level factorial design, pyrolysis and atomization curves, were as follows: aluminum mass of 400 μg, pyrolysis temperature of 400 °C, pyrolysis time of 20 s and 1,800 °C for atomization temperature. Under these conditions, cadmium concentrations could be determined in rice with limits of detection and quantification of 2 and 6 ng g−1, respectively, as well as a characteristic mass of 1.3 pg. The precision, expressed as relative standard deviation (RSD%), was 1.67% for a rice sample with a cadmium concentration of 41.3 ng g−1. The accuracy was confirmed by analysis of a certified reference material of rice flour that was provided by the National Institute for Environmental Studies, Japan. Experiments involving the analyte addition technique demonstrating that the external calibration technique using aqueous standards could be used for quantification of cadmium in rice. The proposed method was used to determine the cadmium content of thirty-four rice samples acquired in supermarkets from Bahia State, Brazil. The rice samples were digested using nitric acid and hydrogen peroxide in a closed system, using a digester block and cold finger. The cadmium concentrations varied from 11.6 to 44.9 ng g−1, with an average content of 30.1 ng g−1. A preliminary study demonstrated that the cadmium contamination in rice decreased after cooking using a microwave oven.

Analytical strategies for determination of cadmium in Brazilian vinegar samples using ET AAS

This paper proposes two methods for determination of cadmium in vinegar employing electrothermal atomic absorption spectrometry. The optimization step was performed using two-level full factorial and Box-Behnken designs, being that a new multiple response function was established. Under experimental conditions of pyrolysis temperature of 640 °C and atomization temperature of 2000 °C, the direct method allows the analysis using the external calibration technique, with limit of quantification of 14 ng L(-1) and characteristic mass of 1.2 pg, having aluminium as chemical modifier. This method was applied in six samples of vinegar acquired from Salvador City, Brazil. The cadmium content varied from 20 to 890 ng L(-1). Other method was also proposed by digestion using nitric acid and hydrogen peroxide in reflux system employing cold finger, being cadmium determined by ETAAS. The results obtained with the complete digestion procedure were in agreement with those found by the direct method proposed herein.

Multi-commuted flow system for cadmium determination in natural water by cold vapour atomic absorption spectrometry

The present paper proposes the use of a multi-syringe flow injection analysis (MSFIA) system for the determination of Cd in natural water by cold vapour atomic absorption spectrometry (CV-AAS). The chemical and physical conditions for vapour generation were investigated and optimized using multivariate optimization methodology. Some complexing reagents were tested as additives to increase the analytical signal. Thiourea showed a positive effect, whereas L-cysteine reduced the signal of Cd. The method allows the direct determination of Cd, i.e. without sample pre-concentration, with limits of detection and quantification of 5.8 and 19.3 ng L−1, respectively, and employing external calibration technique. The precision expressed as a relative standard deviation varied between 1.4% and 2.9% for two levels of cadmium (0.25 and 2.5 μg L−1). Using 2 mL of sample volume, an injection throughput of 87 h−1 was achieved. The accuracy was confirmed by the analysis of a certified reference sample of seawater (CASS-4) furnished by National Research Council of Canada and addition/recovery tests, obtaining recoveries between 94% and 101%. The method was satisfactorily applied for the determination of Cd in seawater and ground water samples from Mallorca, Spain.

On-line simultaneous pre-concentration procedure for the determination of cadmium and lead in drinking water employing sequential multi-element flame atomic absorption spectrometry

An on-line pre-concentration system for the sequential determination of cadmium and lead in drinking water by using fast sequential flame atomic absorption spectrometry (FS-FAAS) is proposed in this paper. Two minicolums of polyurethane foam loaded with 2-(6-methyl-2-benzothiazolylazo)-orcinol (Me-BTAO) were used as sorptive pre-concentration media for cadmium and lead. The analytical procedure involves the quantitative uptake of both analyte species by on-column chelation with Me-BTAO during sample loading followed by sequential elution of the analytes with 1.0 mol L−1 hydrochloric acid and determination by FS-FAAS. The optimisation of the entire analytical procedure was performed using a Box–Behnken multivariate design utilising the sampling flow rate, sample pH and buffer concentration as experimental variables. The proposed flow-based method featured detection limits (3σ) of 0.08 and 0.51 µg L−1 for cadmium and lead, respectively, precision expressed as relative standard deviation (RSD) of 1.63% and 3.87% (n = 7) for cadmium at the 2.0 µg L−1 and 10.0 µg L−1 levels, respectively, and RSD of 6.34% and 3.26% (n = 7) for lead at the 5.0 µg L−1 and 30.0 µg L−1 levels, respectively. The enrichment factors achieved were 38.6 and 30.0 for cadmium and lead, respectively, using a sample volume of 10.0 mL. The sampling frequency was 45 samples per hour. The accuracy was confirmed by analysis of a certified reference material, namely, SRM 1643d (Trace elements in natural water). The optimised method was applied to the determination of cadmium and lead in drinking water samples collected in Santo Amaro da Purificação City, Bahia, Brazil.

Determination of copper in airborne particulate matter using slurry sampling and chemical vapor generation atomic absorption spectrometry.

The present paper describes the development of a method for the determination of copper in airborne particulate matter using slurry sampling and chemical vapor generation atomic absorption spectrometry (CVG AAS). Chemometric tools were employed to characterize the influence of several factors on the generation of volatile copper species. First, a two-level full factorial design was performed that included the following chemical variables: hydrochloric acid concentration, tetrahydroborate concentration, sulfanilamide concentration and tetrahydroborate volume, using absorbance as the response. Under the established experimental conditions, the hydrochloric acid concentration had the greatest influence on the generation of volatile copper species. Subsequently, a Box-Behnken design was performed to determine the optimum conditions for these parameters. A second chemometric study employing a two-level full factorial design was performed to evaluate the following physical factors: tetrahydroborate flow rate, flame composition, alcohol volume and sample volume. The results of this study demonstrated that the tetrahydroborate flow rate was critical for the process. The chemometric experiments determined the following experimental conditions for the method: hydrochloric acid concentration, 0.208 M; tetrahydroborate concentration, 4.59%; sulfanilamide concentration, 0.79%; tetrahydroborate volume, 2.50 mL; tetrahydroborate flow rate, 6.50 mL min(-1); alcohol volume, 200 µL; and sample volume, 7.0 mL. Thus, this method, using a slurry volume of 500 µL and a final dilution of 7 mL, allowed for the determination of copper with limits of detection and quantification of 0.30 and 0.99 µg L(-1), respectively. Precisions, expressed as RSD%, of 4.6 and 2.8% were obtained using copper solutions at concentrations of 5.0 and 50.0 µg L(-1), respectively. The accuracy was evaluated by the analysis of a certified reference material of urban particulate matter. The copper concentration obtained was 570±63 mg kg(-1), and the certified value was 610±70 mg kg(-1). This method was applied for the determination of copper in airborne particulate matter samples collected in two Brazilian regions of Bahia State, Brazil. The copper contents found varied from 14.46 to 164.31 ng m(-3).

Analytical Strategies for Determination and Environmental Impact Assessment of Inorganic Antimony Species in Natural Waters Using Hydride Generation Atomic Fluorescence Spectrometry (HG AFS)

This study proposes an optimized procedure for the determination of inorganic antimony species in natural waters using hydride generation atomic fluorescence spectrometry (HG AFS) and continuous flow system. The variables of the hydride generation system, such as pre-reduction time, hydrochloric acid concentration and sodium tetrahydroborate concentration, were evaluated using full factorial design at two levels and Doehlert design. After optimized experimental conditions, the method allowed the determination of antimony with limits of detection and quantification of 9 and 30 ng L, respectively. The precision (RSD) of the method was < 5% and the accuracy was confirmed by the analysis of certified reference material (SLRS-4, River water for trace metals). The method was successfully applied for inorganic antimony speciation in water samples collected in Salvador City, Bahia State, Brazil. In mineral water, total Sb concentrations ranged from 0.26 to 0.30 μg L, whereas the concentrations of Sb were below 0.03 μg L. On the other hand, in natural surface waters, the quantifiable concentration of total Sb and Sb ranged from 0.41 to 1.23 μg L and 0.23 to 1.04 μg L, respectively. The highest average concentrations of Sb were obtained in regions with the largest urban influence, ratifying the anthropogenic impact in water bodies.

Simultaneous determination of mercury and selenium in fish by CVG AFS

In this work, an analytical method was proposed for the simultaneous determination of mercury and selenium in fish samples using Atomic Fluorescence Spectrometry (AFS). Multivariate designs were performed to evaluate the variables and optimize the best condition of chemical vapor generation (CVG) and simultaneous determination of mercury and selenium by AFS. Fish samples were prepared via acid digestion in digester block with cold finger reflux system, which ensured that the elements were not lost by volatility. The proposed analytical method was validated, and excellent figures of merit have been achieved, such as detection limits of 0.33 and 9.18 ng g-1 for mercury and selenium, respectively. The method was applied for simultaneous determination of mercury and selenium in canned sardines. Mercury concentrations ranged from 0.057 to 0.203 μg g-1 and selenium concentration from 1.76 to 2.21 μg g-1, providing a mean molar ratio (Se:Hg) equivalent to 36.