Alailson F. Dantas

Nickel determination in saline matrices by ICP-AES after sorption on Amberlite XAD-2 loaded with PAN.

In the present paper, a solid phase extraction system for separation and preconcentration of nickel (ng g(-1)) in saline matrices is proposed. It is based on the adsorption of nickel(II) ions onto an Amberlite XAD-2 resin loaded with 1-(2-pyridylazo)-2-naphthol (PAN) reagent. Parameters such as the pH effect on the nickel extraction, the effect of flow rate and sample volume on the extraction, the sorption capacity of the loaded resin, the nickel desorption from the resin and the analytical characteristics of the procedure were studied. The results demonstrate that nickel(II) ions, in the concentration range 0.10-275 microg l(-1), and pH 6.0-11.5, contained in a sample volume of 25-250 ml, can be extracted by using 1 g Amberlite XAD-2 resin loaded with PAN reagent. The adsorbed nickel was eluted from the resin by using 5 ml 1 M hydrochloric acid solution. The extractor system has a sorption capacity of 1.87 mumol nickel per g of Amberlite XAD-2 resin loaded with PAN. The precision of the method, evaluated as the R.S.D. obtained after analyzing a series of seven replicates, was 3.9% for nickel in a concentration of 0.20 microg ml(-1). The proposed procedure was used for nickel determination in alkaline salts of analytical grade and table salt, using an inductively coupled plasma atomic emission spectroscopy technique (ICP-AES). The standard addition technique was used and the recoveries obtained revealed that the proposed procedure shows good accuracy.

Copper determination in natural water samples by using FAAS after preconcentration onto amberlite XAD-2 loaded with calmagite.

A procedure for separation and preconcentration of trace amounts of copper in natural water samples, has been proposed. It is based on the adsorption of copper(II) ions onto a column of Amberlite XAD-2 resin loaded with calmagite reagent. This way amounts of copper within the range from 0.0125 to 25.0 microg, in a sample volume of 25 to 250 ml, and pH from 3.7 to 10.0 was concentrated as calmagite complex in a column of 0.50 g of Amberlite XAD-2 resin. Copper (II) ion was desorpted by using 5.0 ml of 2 mol l(-1) hydrochloric acid. Detection and determination limits of the proposed procedure for 250 ml sample volume were 0.15 and 0.50 microg l(-1), respectively. Selectivity test showed that (in the indicated concentration), calcium(II) (500 mg l(-1)), magnesium(II) (500 mg l(-1)), strontium(II) (50 mg l(-1)), iron(III) (10 mg l(-1)), nickel(II) (10 mg l(-1)), cobalt(II) (10 mg l(-1)), cadmium(II) (10 mg l(-1)) and lead(II) (10 mg l(-1)) did not interfere in copper determination by this procedure. Precision of the method, evaluated as the relative standard deviation by analyzing a series of seven replicates, was 2.42% for a copper mass of 1.0 microg in a sample volume of 100 ml. The accuracy of the proposed procedure was evaluated by means of copper determination in reference biological samples. The achieved results were in good agreement with certified values. The extractor system had a sorption capacity of 1.59 mumol of copper per gram of resin loaded with calmagite. The proposed procedure was applied for copper determination by FAAS in natural water samples. Samples were collected from different places of Salvador city, Bahia, Brazil. The achieved recovery, measured by the standard addition technique, showed that the proposed procedure had good accuracy. A good enrichment factor (50x) and simplicity are the main advantages in this analytical procedure.

Multivariate optimization of ultrasound-assisted extraction for determination of Cu, Fe, Ni and Zn in vegetable oils by high-resolution continuum source atomic absorption spectrometry.

An assisted liquid-liquid extraction of copper, iron, nickel and zinc from vegetable oil samples with subsequent determination by high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS) was optimized by applying a full factorial design in two levels and the response surface methodology, Box-Behnken. The effects of the acid concentration and the amplitude, cycle and time of sonication on the extraction of the analytes, as well as their interactions, were assessed. In the selected condition (sonication amplitude = 66%, sonication time = 79 s, sonication cycle = 74%), using 0.5 mol L(-1) HCl as the extractant, the limits of quantification were 0.14, 0.20, 0.21 and 0.04 μg g(-1) for Cu, Fe, Ni and Zn, respectively, with R.S.D. ranging from 1.4% to 3.6%. The proposed method was applied for the determination of the analytes in soybean, canola and sunflower oils.

Multi-element determination of copper, iron, nickel, manganese, lead and zinc in environmental water samples by ICP OES after solid phase extraction with a C18 cartridge loaded with 1-(2-pyridylazo)-2-naphthol

A pre-concentration solid-phase procedure has been developed for the sensitive and simple determination of copper, iron, nickel, manganese, lead and zinc in environmental water samples by inductively coupled plasma optical emission spectrometry (ICP OES). After pH adjustment, the samples were percolated with the aid of a peristaltic pump on a Sep-Pak C18 cartridge loaded with 1-(2-pyridylazo)-2-naphthol (PAN). The analyte elution was carried out with the passage of HCl through the cartridge for subsequent determination by ICP OES. The experimental conditions for pre-concentration were optimized considering the following factors: the concentration and volume of the eluent, sample volume, flow-rate and pH. The optimized conditions corresponded to the use of 5 mL of 0.8 M HCl as the eluent, a sample volume of 50 mL, a flow-rate of 1.9 mL min−1 and pH 9.0. Under these conditions, the detection limits for Cu, Fe, Mn, Ni, Pb and Zn varied between 0.11 and 21 μg L−1. The relative standard deviation (RSD) for the analytes of this study did not exceed 9%, after the application of the proposed pre-concentration procedure (n = 10, 0.50 mg L−1). The effect of possible interfering species on the recovery of the analytes was also investigated. The accuracy of the method was evaluated by the analysis of a certified reference material (SLEW-3 Estuarine Water Reference Material for Trace Metals) and the proposed method was applied to samples of groundwater, drinking water and river water. The samples were analyzed by using inductively coupled plasma mass spectrometry (ICP-MS) as a comparative method and no significant differences among these results and the results obtained by the proposed method were observed.

Spectrophotometric determination of zinc in copper-base alloys with TAN

TAN reacts with zinc(II) forming a red complex with composition 1:2 Zn(II)-TAN and absorption maximum at 582 nm. Zinc can be determined with this reagent in the presence of Triton X-100, in the pH range 6.20-8.00 with a molar absorptivity of 4.5×104 l/mol/cm Beers Law was obeyed up to least 1.55 μg/ml. Copper interference was eliminated with a mixture of thiosulfate and ascorbic acid and nickel separated by precipitation with dimethylglyoxime. The proposed method was used for zinc determination in several copper-base alloys and the results of analysis in comparison with certified values indicated that the procedure was accurate and precise. A derivative procedure is also proposed, allowing zinc determination with high sensitivity (5-400 ng/ml).

Spectrofotometric determination of copper in sugar cane spirit using biquinoline in the presence of ethanol and Triton X-100.

The present paper proposes a method for molecular spectrophotometric determination of copper in sugar cane spirits. The copper(I) reacts with biquinoline forming a pink complex with maximum absorption at 545 nm. The reaction occurs in the presence of hydroxylamine, ethanol and Triton X-100 tensioative. Determination of copper is possible in a linear range 0.2-20.0 mgL(-1) with a detection limit 0.05 mgL(-1). The great advantages of the proposed methodology are the elimination of liquid-liquid extraction step and the use of toxic organics solvents, like dioxane, to dissolve the reagent.

Comparison of Spectrophotometric Methods for the Determination of Copper in Sugar Cane Spirit.

Three spectrophotometric methods were developed for the determination of copper (Cu) in sugar cane spirit using the chromogenic reagents neocuproine, cuprizone, and bathocuproine. Experimental conditions, such as reagent concentration, reducer concentration, pH, buffer concentration, the order of addition of reagents, and the stability of the complexes, were optimized. The work range was established from 1.0 to 10.0 µg/mL, with correlation coefficients of >0.999 for all three optimized methods. The methods were evaluated regarding accuracy by addition and recovery tests at five concentration levels, and the obtained recoveries ranged from 91 to 105% (n = 3). Precision was expressed as RSD (relative standard deviation), with values ranging from 0.01 to 0.17% (n = 10). The method using the chromogenic reagent cuprizone presented the greatest molar absorptivity, followed by bathocuproine and neocuproine. The methods were applied for the determination of Cu in sugar cane spirit, and the results were compared with a reference method by flame atomic absorption spectrometry (FAAS). Calibration curve solutions for FAAS analysis were prepared in a 40% (v/v) alcohol medium in a range of concentrations from 0.5 up to 5 µg/mL. Measurements for Cu determination were carried out at a wavelength of 324.7 nm. The concentrations obtained for Cu in sugar cane spirit samples from Brazil were between 1.99 and 12.63 µg/mL, and about 75% of the samples presented Cu concentrations above the limit established by Brazilian legislation (5.0 µg/mL or 5.0 mg/L).

Determinação espectrofotométrica de sulfato em álcool etílico combustível empregando dibromosulfonazo III

A sensitive spectrophotometric method was developed for sulphate determination in automotive ethanol fuel. The method based on the reaction of the analyte with barium-dibromosulphonazo(III) complex lead to a decrease in the magnitude of the absorbance signals monitored at 649 nm. No sample pretreatment is required and the proposed method allows sulphate determination in the 0.45 - 6.50 mg L-1 range with R.S.D. < 2% and limit of detection of 0.14 mg L-1. The method has been successfully applied for sulphate determination in automotive ethanol fuel and the results agreed with the reference chromatographic method.

Use of nitroanilines for spectrophotometric determination of ethinylestradiol in pharmaceutical formulations

Three nitroanilines (2-methoxy-4-nitroaniline, 2,4-dinitroaniline and 2-methyl-4-nitroaniline) were tested as spectrophotometric reagents for determination of ethinylestradiol (ETE). The determinations were based on absorbance measurments of the reaction product obtained from the coupling of each diazotized nitroaniline with ETE. Optimization of temperature, pH and diazotization coupling reaction time was realized. 2-Methyl-4-nitroaniline provided the more sensitive system for ETE spectrophotometric determination at 531 nm and the analytical response was linear in the concentration range of 0.65–10.0 µg ml−1. The limit of detection and coefficient of variation were estimated as 197 µg l−1 and 4.5%, respectively. The results showed that the proposed method is simple and rapid, allowing selective determination of analyte. The method successfully determined ETE in oral contraceptive formulations.

Uso do violeta de alizarina N (AVN) como reagente espectrofotométrico na determinação de alumínio

The present work proposes the application of the 4-Hidroxy-3-(2-hydroxynaphtylazo)-benzenesulphonic acid (C.I. 15670), Alizarine Violet N (AVN), as a reagent for direct aluminium determination using molecular absorption spectrophotometry in the presence of tensoatives. Al(III) cation reacts with AVN in pH 9.4, forming a red complex, stable for at least 24 hours, with absorption minimum at 607nm and, against a reagent blank, (ecomplex - ereagent) = -2.71x104 L.mol-1.cm-1. The reaction occurs in the presence of a Triton-X100 and CTAB tensoatives mixture, in the presence of EDTA. Al(III) determination is possible in the linear range of 50 up to 400ng.mL-1, with a detection limit of 41 ng.mL-1.