A method for the determination of nickel in water was developed. The procedure involves preconcentration of nickel by using dispersive liquid-liquid microextraction. The Ni(II) ions were extracted in chloroform in the form of complex with the reagent 2-(2 0 -benzothiazolylazo)-p-cresol. Ethanol was used as the disperser solvent. After injection of the extracting mixture in a solution of nickel, a cloudy mixture was observed. A quick centrifugation induces phase separation and thus the settling of rich phase. The nickel content in the rich phase is measured by flame atomic absorption spectrometry. Under optimal conditions, the limit of detection and quantification obtained were 1.4 and 4.7 mg L À1 , respectively. Some parameters used to characterize preconcentration systems, such as enrichment factor and consumption index were calculated and resulted in 29 and 0.34 mL, respectively. After optimization of variables and determination of analytical characteristics, the method was used for the analysis of certified reference materials (BCR-713: wastewater, effluent and BCR-414: plankton) and real water samples.
A simple method for the determination of mercury in water samples after preconcentration using dispersive liquid-liquid microextraction is described. The procedure is based on the extraction of mercury in the form of a complex and its subsequent determination by spectrophotometry. The complex is formed between Hg(II) and 2-(2-benzothiazolylazo)-p-cresol. The detection at 650 nm is performed directly in the metal-rich phase, which is spread on a triacetylcellulose membrane. The method eliminates the need to use a cuvet or large quantities of samples and reagents. The parameters that influence the preconcentration were studied, and the analytical characteristics were determined. The enrichment factor and the consumptive index for this method were 64 and 0.16 mL, respectively. The LOD (3.3 microg/L) and LOQ (11.1 microg/L) were also determined. The accuracy of the method was tested by the determination of mercury in certified reference materials BCR 397 (Human Hair) and SRM 2781 (Domestic Sludge). The method was applied to the determination of mercury in samples of drinking water, sea water, and river water.
A simple, sensitive and rapid method involving dispersive liquid-liquid microextraction was developed for the determination of molybdenum using electrothermal atomic absorption spectrometry. After injection of a ternary mixture containing trichloroethylene (extractor solvent), ethanol (disperser solvent) and ammonium pyrrolidinedithiocarbamate (chelating reagent), the extraction of molybdenum into the aqueous phase occurs. The quantity of the element in the enriched phase was measured using electrothermal atomic absorption spectrometry. Under optimized conditions (pH 2.5, 2.0 mL of disperser solvent, 50 mL of extraction solvent, 50.0 mL of 0.10% m/v chelating solution and centrifugation at 3000 rpm for 2.5 minutes), the method has a detection limit of 0.013 mg L À1 , a quantification limit of 0.044 mg L À1 and an enrichment factor of 75 for a sample volume of 5.0 mL. The certified reference material NIST 2781, Domestic Sludge, was used to assess the accuracy of the method. The proposed procedure was successfully applied to the determination of molybdenum in natural water samples.
Experimental
InstrumentationAbsorbance measurements were performed using an AAnalyst 400 model atomic absorption spectrometer and an HGA 900 model graphite furnace, both supplied by Perkin Elmer (Shelton, USA). A hollow cathode lamp for molybdenum analysis (Perkin Elmer) was also used. The pH measurements were performed using a Quimis Q400AS pH meter (Diadema, Brazil).
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