Lindomar A. Portugal

Pre-concentration procedure for determination of copper and zinc in food samples by sequential multi-element flame atomic absorption spectrometry.

In this paper is proposed a simultaneous pre-concentration procedure using cloud point extraction for the determination of copper and zinc in food samples employing sequential multi-element flame atomic absorption spectrometry (FS-FAAS). The reagent used is 1-(2-pyridylazo)-2-naphthol (PAN) and the micellar phase is obtained using the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) and centrifugation. The optimization step was performed using Box-Behnken design for three factors: solution pH, reagent concentration and buffer concentration. A multiple response function was established in order to get an experimental condition for simultaneous extraction of copper and zinc. Under the optimized experimental conditions, the method allows the determination of copper with a limit of detection (3sigma(b)/S, LOD) of 0.1 microg L(-1), precision expressed as relative standard deviation (R.S.D.) of 2.1 and 1.3% (N=10), for copper concentrations of 10 and 50 microg L(-1), respectively. Zinc is determined with a LOD of 0.15 microg L(-1) and precision as R.S.D. of 2.7 and 1.7% for concentrations of 10 and 50 microg L(-1), respectively. The enhancement factors obtained were 36 and 32 for copper and zinc, respectively. The accuracy was assessed by analysis of certified reference materials, namely, SRM 1567a - Wheat Flour and SRM 8433 - Corn Bran from National Institute of Standards & Technology and BCR 189-wholemeal flour from Institute of Reference Materials and Measurements. The method was applied to the determination of copper and zinc in oats, powdered chocolate, corn flour and wheat flour samples. The copper content in the samples analyzed varied from 1.14 to 3.28 microg g(-1) and zinc from 8.7 to 22.9 microg g(-1).

Determination of mercury in rice by MSFIA and cold vapour atomic fluorescence spectrometry

In the present paper the use of a MSFIA system for determination of mercury in rice by cold vapour atomic fluorescence spectrometry (CV AFS) is proposed. The sample digestion is performed in a microwave oven using nitric acid and hydrogen peroxide. The experimental conditions for vapour generation were determined using a full two-level factorial design involving the following factors: nitric acid and tin chloride concentrations and sample flow rate. Employing the conditions optimised, the method allows the determination of mercury using the external calibration technique with aqueous standards. The reached limits of detection and quantification were 0.48 and 1.61 ng g⁻¹ respectively, and the precision (as relative standard deviation) was 3.28% and 1.56% for rice samples with a mercury content of 3.63 and 5.81 ng g⁻¹, respectively. The method accuracy was confirmed analysing a certified reference material of rice flour furnished by National Institute of Standard and Technology. The interference of nitrous acid and nitrous oxides are removed using potassium dichromate. The method was applied to mercury determination in twelve rice samples acquired in Palma de Mallorca (Spain) between the months of January and April of 2012. The mercury content found varied from 2.15 to 7.25 ng g⁻¹. These results agree with those reported by others authors.

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.

On-line lab-in-syringe cloud point extraction for the spectrophotometric determination of antimony☆

Most of the procedures for antimony determination require time-consuming sample preparation (e.g. liquid-liquid extraction with organic solvents), which are harmful to the environment. Because of the high antimony toxicity, a rapid, sensitive and greener procedure for its determination becomes necessary. The goal of this work was to develop an analytical procedure exploiting for the first time the cloud point extraction on a lab-in-syringe flow system aiming at the spectrophotometric determination of antimony. The procedure was based on formation of an ion-pair between the antimony-iodide complex and H(+) followed by extraction with Triton X-114. The factorial design showed that the concentrations of ascorbic acid, H2SO4 and Triton X-114, as well as second and third order interactions were significant at the 95% confidence level. A Box-Behnken design was applied to obtain the response surfaces and to identify the critical values. System is robust at the 95% confidence level. A linear response was observed from 5 to 50 µg L(-1), described by the equation A=0.137+0.050C(Sb) (r=0.998). The detection limit (99.7% confidence level), the coefficient of variation (n=5; 15 µg L(-1)) and the sampling rate was estimated at 1.8 µg L(-1), 1.6% and 16 h(-1), respectively. The procedure allows quantification of antimony in the concentrations established by environmental legislation (6 µg L(-1)) and it was successfully applied to the determination of antimony in freshwater samples and antileishmanial drugs, yielding results in agreement with those obtained by HGFAAS at the 95% confidence level.

A Multiple Response Function for Optimization of Analytical Strategies Involving Multi-elemental Determination

Fil: Novaes, Cleber G.. Universidade Estadual do Sudoeste da Bahia; Brasil. Universidade Federal da Bahia; Brasil

Submicrometric Magnetic Nanoporous Carbons Derived from Metal–Organic Frameworks Enabling Automated Electromagnet-Assisted Online Solid-Phase Extraction

We present the first application of submicrometric magnetic nanoporous carbons (μMNPCs) as sorbents for automated solid-phase extraction (SPE). Small zeolitic imidazolate framework-67 crystals are obtained at room temperature and directly carbonized under an inert atmosphere to obtain submicrometric nanoporous carbons containing magnetic cobalt nanoparticles. The μMNPCs have a high contact area, high stability, and their preparation is simple and cost-effective. The prepared μMNPCs are exploited as sorbents in a microcolumn format in a sequential injection analysis (SIA) system with online spectrophotometric detection, which includes a specially designed three-dimensional (3D)-printed holder containing an automatically actuated electromagnet. The combined action of permanent magnets and an automatically actuated electromagnet enabled the movement of the solid bed of particles inside the microcolumn, preventing their aggregation, increasing the versatility of the system, and increasing the preconcentration efficiency. The method was optimized using a full factorial design and Doehlert Matrix. The developed system was applied to the determination of anionic surfactants, exploiting the retention of the ion-pairs formed with Methylene Blue on the μMNPC. Using sodium dodecyl sulfate as a model analyte, quantification was linear from 50 to 1000 μg L(-1), and the detection limit was equal to 17.5 μg L(-1), the coefficient of variation (n = 8; 100 μg L(-1)) was 2.7%, and the analysis throughput was 13 h(-1). The developed approach was applied to the determination of anionic surfactants in water samples (natural water, groundwater, and wastewater), yielding recoveries of 93% to 110% (95% confidence level).

A portable multi-syringe flow system for spectrofluorimetric determination of iodide in seawater

A miniaturized analyzer encompassing a poly(methyl methacrylate) chip with integrated spectrofluorimetric detection and solutions propelling by a multi-syringe module is proposed. Iodide was determined through its catalytic effect on the reaction between Ce(IV) and As(III). Matrix isopotential synchronous fluorescence was explored to set the excitation and emission wavelengths. A two-level full factorial design allowed to evaluate the significance of variables (Ce(IV), As(III) and H2SO4 concentrations) and their interaction effects in the experimental domain. A Doehlert Matrix was applied to identify the critical values. The optimized procedure showed a linear response from 1 to 100 μg L(-1) (S=53.7+2.61C, in which S is the net fluorescence and C is iodide concentration in μg L(-1)). Detection limit, coefficient of variation (n=6) and sampling rate were estimated at 0.3 μg L(-1), 0.8% and 20 h(-1), respectively. Recoveries within 90-117% were estimated for iodide spiked to seawater samples. The proposed procedure stands out because of the portability, robustness, and simplicity for in-field analysis of iodide in seawater.

Parabens determination in cosmetic and personal care products exploiting a multi-syringe chromatographic (MSC) system and chemiluminescent detection

Parabens are widely used in dairy products, such as in cosmetics and personal care products. Thus, in this work a multi-syringe chromatographic (MSC) system is proposed for the first time for the determination of four parabens: methylparaben (MP), ethylparaben (EP), propylparaben (PP) and butylparaben (BP) in cosmetics and personal care products, as a simpler, practical, and low cost alternative to HPLC methods. Separation was achieved using a 5mm-long precolumn of reversed phase C18 and multi-isocratic separation, i.e. using two consecutive mobile phases, 12:88 acetonitrile:water and 28:72 acetonitrile:water. The use of a multi-syringe buret allowed the easy implementation of chemiluminescent (CL) detection after separation. The chemiluminescent detection is based on the reduction of Ce(IV) by p-hydroxybenzoic acid, product of the acid hydrolysis of parabens, to excite rhodamine 6G (Rho 6G) and measure the resulting light emission. Multivariate designs combined with the concepts of multiple response treatments and desirability functions have been employed to simultaneously optimize and evaluate the responses. The optimized method has proved to be sensitive and precise, obtaining limits of detection between 20 and 40 µg L(-1) and RSD <4.9% in all cases. The method was satisfactorily applied to cosmetics and personal care products, obtaining no significant differences at a confidence level of 95% comparing with the HPLC reference method.

Development of a MSFIA system for sequential determination of antimony, arsenic and selenium using hydride generation atomic fluorescence spectrometry.

This paper proposed a multisyringe flow injection analysis (MSFIA) system for antimony, arsenic and selenium determination in peanut samples by hydride generation atomic fluorescence spectrometry (HG-AFS). The optimization step of the hydride generation was performed using a two-level full factorial design involving the parameters: hydrochloric acid, sodium tetrahydroborate and potassium iodide concentrations. So, using the chemical conditions optimized, this method allows the determination of these elements employing the external calibration technique using aqueous standards with limits of detection and quantification of 0.04 and 0.14µgL(-1) for antimony, 0.04 and 0.14µgL(-1) for arsenic and 0.14 and 0.37µgL(-1) for selenium, respectively. Additionally, the effect of vanadium, chromium, cobalt, nickel, zinc, copper, iron and molybdenum on the generation of chemical vapour was also studied. The precision expressed as relative standard deviation varied from 1.2 to 3.6% for antimony, 1.8-3.9% for arsenic and 1.8-2% for selenium. The accuracy for arsenic and selenium was confirmed using the certified peach leaves reference material SRM 1547 produced by National Institute of Standard and Technology. The proposed method showed 45 injection throughput (h(-1)) using 1.6mL sample volume for each element, 0.8mL NaBH4 0.5% (w/v) containing NaOH 0.05% (w/v), 0.8mL HCl 5M and 0.4mL KI 14% (w/v) containing L-ascorbic acid 2.5% (w/v). The method was applied to the determination of antimony, arsenic and selenium in peanut samples, which were firstly lyophilized and afterward digested using microwave assisted radiation. Six samples were analyzed and the contents of the elements found were: 28.7-41.3µgkg(-1) for arsenic, 86.4-480.1µgkg(-1) for selenium and 32.6-52.4µgkg(-1) for antimony. Addition/recovery tests were also performed to confirm the method accuracy for the three elements.

A non-chromatographic automated system for antimony speciation in natural water exploiting multisyringe flow injection analysis coupled with online hydride generation – atomic fluorescence spectrometry

A non-chromatographic automated system for the speciation and determination of inorganic and trimethylantimony (TMSb) exploiting multisyringe flow injection analysis (MSFIA) with hydride generation (HG) and atomic fluorescence spectrometry (AFS) is described. A cationic minicolumn was used for retaining the methylated forms of Sb which can generate hydrides, minimizing errors in the inorganic antimony speciation step. The optimization was performed in a multivariate way by employing a three-variable Box–Behnken design and a multiple response strategy. So, this method allows the quantification of Sb using the external calibration with aqueous standards. The method is suitable for monitoring drinking, surface and ground waters according to regulations established by the EU directives for antimony (5.0 μg L−1), and it was applied to the speciation of inorganic antimony and TMSb in several spiked water samples with recoveries close to 100%. The detection limits were 0.03 μg L−1 for Sb(III) and Sb(V) and 0.13 μg L−1 for TMSb. The method was satisfactorily applied to the determination of Sb(III), Sb(V) and TMSb in different water samples collected in Balearic Islands, Spain.