A newly analytical method has been developed to determine total chromium and speciation of this element in water samples through dispersive liquid-liquid microextraction combined with a high-resolution continuum source flame atomic absorption spectrometry. The most significant variables affecting complexation and extraction were optimized by using response surface methodology and univariate optimization. The best conditions for both the complexation and extraction elements in this study were: complexing agent ammonium pyrrolidine dithiocarbamate (APDC 6.0 mmol L-1); pH at 2.0 (CrVI) and at 7.0 (Cr total); NaCl (5% m/v); 1-undecanol (50 µL) and ethanol 300 (CrIV) and 275 µL (total Cr). Under optimal conditions, this method resulted in a 20-100 µg L-1 linear range for CrVI and total chromium, detection limits of 0.35 (CrVI) and 6.7 µg L-1 (total Cr), as well as enriching factor of 26 (CrVI) and 19 for total Cr. The method accuracy was carried out by using certified water reference material (NIST CRM 1643e), and the results achieved were in agreement with the certified value (t-test at a confidence interval of 95%). The method developed was applied in samples of mineral water, tap water (the recovery values ranged from 88 to 115%) and seawater.

Cloud point extraction was employed for the separation and preconcentration of cadmium and lead prior to the determination by thermospray flame atomic absorption spectrometry. Di-2- pyridyl ketone salicyloylhydrazone (DPKSH) was used as complexing agent and the cadmium and lead complexes were extracted from the aqueous phase by the Triton X-114 surfactant. The variables associated with the preconcentration (pH as well as DPKSH, surfactant and electrolyte concentration) were optimized by using a full factorial design with two levels, four variables and a central composite. Under the optimized conditions, a sample volume of 100 µL was introduced into a hot Ti tube at a flow rate of 0.6 mL min-1 and the integrated absorbance was measured. Calibration curves were obtained with linear ranges of 0.075-2.0 µg L−1 (Cd) and 2.5-100 µg L−1 (Pb). The detection limits of 0.04 µg L−1 (Cd) and 1.3 µg L−1 (Pb) (99.7% confidence level) were obtained. The proposed method was applied to hemodialysis solutions and water samples. The accuracy of the method was evaluated by analyzing a certified reference material (NIST CRM 1643e) and the results were in agreement with the certified values at a 95% confidence level according to t-test.

A adsorção do DPKSH em resina aniônica foi investigada a 25 ± 1 ºC e em pH 12 com base em três modelos cinéticos pseudo-primeira ordem, pseudo-segunda ordem e difusão intra-partícula. Os dados experimentais foram aplicados com sucesso aos modelos das isotermas de Langmuir, Freundlich e Dubinin-Radushkevich (D-R). A resina aniônica modificada com DPKSH foi usada na determinação espectrofotométrica do cobre após pré-concentração em linha. Nas melhores condições, foi observada uma resposta linear entre 20 e 80 µg L-1, limites de detecção e quantificação estimados em 0,5 e 1,8 µg L-1, respectivamente, com um nível de confiança de 95%, e um fator de pré-concentração igual a 11. O desvio padrão relativo foi estimado em 2,6% para a concentração de 32 µg L-1 Cu(II) (n = 20). Os resultados obtidos na determinação de cobre em amostras de etanol combustível apresentaram concordância, com um nível de confiança de 99%, aos obtidos por espectrometria de absorção atômica com chama (F AAS).

The adsorption of DPKSH onto anionic resin was investigated at 25 ± 1 ºC and pH 12 on the basis of three kinetic models including pseudo-first order, pseudo-second order and intraparticle diffusion. Isotherm equations including Langmuir, Freundlich and Dubinin-Radushkevich (D-R) were successfully applied to model the experimental data. An anionic resin loaded with DPKSH was used in a flow system for the in-line concentration of copper prior to spectrophotometric determination. Under optimized conditions, a linear response was observed between 20 and 80 µg L-1, with limits of detection and quantification estimated at 0.5 and 1.8 µg L-1, respectively, at the 95% confidence level with an enrichment factor of 11. The relative standard deviation was estimated to be 2.6% for 32 µg L-1 Cu(II) (n = 20). The results obtained for copper determination in ethanol fuel samples agreed with those achieved by flame atomic absorption spectrometry (F AAS) at the 99% confidence level.

O ligante di-2-piridil cetona benzoilhidrazona (DPKBH) é frequentemente usado para determinação de íons metálicos de transição em amostras ambientais. Devido a sua baixa solubilidade em água, é utilizado em solução aquo-etanólica (1:1) e com pH adequadamente ajustado para resultar na maior sensibilidade. As propriedades do DPKBH devem ser conhecidas em diferentes porcentagens de etanol, para que se estabeleçam as condições de maior sensibilidade e/ou seletividade para análise de metais. O comportamento ácido-base desse reagente em solvente aquo-etanólico, as constantes de dissociação/ionização (pK1 e pK2) do DPKBH foram determinados em diferentes soluções do solvente aquo-etanólico(10, 20, 30 e 50% V/V de etanol, fazendo-se titulações potenciométricas em 25,0 +/- 0,1ºC. Os valores de pK1 e pK2 aumentaram em funçào do aumento da porcentagem de etanol, de 10 a 30%, mas diminuiram para 50% de solvente orgânico. Os resultados são correlacionados à composição do meio e seus efeitos.

The ligand di-2-pyridyl ketone benzoylhydrazone (DPKBH) is widely used for the determination of transition metal ions in environmental samples. Due to its low solubility in water it is used in aqueous-ethanol (1:1) solvent and for higher sensitivity the pH must be properly adjusted. The properties of DPKBH solutions must be known at different ethanol-water percentages in order to achieve higher sensitivity and/or selectivity for metal analysis. The acid-base behavior of this reagent in aqueous-ethanol solvent and the dissociation/ionization constants (pK1 and pK2) of DPKBH have been determined in different aqueous-ethanol solvent mixtures (10, 20, 30 and 50 % V/V of ethanol) from potentiometric titrations at 25.0 ± 0.1° C. As the amount of ethanol increases from 10 to 30% the pK1 and pK2 values increased, but they decreased in 50% of the organic solvent. The results are correlated with the medium composition and its effects.