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.

Analytical chemists frequently receive samples that cannot be analyzed in the natural state, due to the presence of interferences and/or inadequate sensibility of the available analytical methodology. Previous steps for separation and enrichment are almost always necessary, and many procedures have been proposed. The process, involving extraction in solid phase, has received more acceptance due to a number of possible advantages, including the availability and easy recovery of the solid phase, attainability of large preconcentration factors and the facility for separation and enrichment using systems with continuous flow. Besides, they usually do not need organic solvents, which may be toxic. For cobalt adsorption determination, several procedures have been proposed involving polyurethane foam 1 , activated carbon 2,3 , Amberlite XAD-4 resin 4,5 , naphthalene 6 and C 18 -bonded silica gel column; 7,8 other techniques as coprecipitation using indium hydroxide as colector 9 , liquid-liquid extraction 10 and cobalt separation as complex and filtration with a menbrane filter.

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 mg ml À1 . The limit of detection and coefficient of variation were estimated as 197 mg l À1 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.