Abstract
The detailed investigation of a sensitive and selective spectrophotometric method for the determination of trace amounts of cerium is described. The method is based on the reaction of cerium(III) with arsenazo ш in the presence of sodium dodecyl sulphate surfactant at pH 3.0 to form a blue-greenish coloured chelate absorbing maximum at 653 nm. Beer’s law is obeyed over the range (5-70) µg /25 ml, with a molar absorptivity of (4.99×10 4 ) l.mol 1 .cm -1 and the coefficient of determination (r 2 ) is 0.9994, Sandell ’ s sensitivity index is (28.08×10 -4 ) µg.cm -2 , a relative error of (0.0-0.2%) and a relative standard deviation of (0.0 to +2.1)%, depending on the concentration levels in the calibration curve. The method has been applied successfully to determine cerium in sea water and some synthetic alloys.
Highlights
Cerium is the most abundant rare earth element, and is a silvery metal, belonging to the lanthanide group
Preliminary investigations The visible spectra of the blue-greenish coloured chelate were measured immediately after mixing 50 μg of cerium (ш) solution (M), 3ml of (1×10-4M) arsenazo ш (R) and 1ml of 0.01 M HCl and showed an absorption band at 653 nm, which indicates a definite reaction between Ce (ш) and Arsenazo ш reagent (Az ш) reagent in contrast with the reagent blank which shows maximum absorption at 537 nm
Study of the optimum reaction conditions The effect of various parameters on the absorption intensity of the coloured complex as studied and the optimum conditions have been selected for determination of cerium (ш) with arsenazo ш
Summary
Cerium is the most abundant rare earth element, and is a silvery metal, belonging to the lanthanide group. The electrode has a wide linear dynamic range (6.6×10-7 to 6.2×10-2M), with a low detection limit (2.3×10-7 M) This sensor was applied to determination of fluoride ion in pharmaceutical samples and of cerium content in stainless steel samples (Karami, 2003). Colorimetric method for the determination of cerium (IV) ions with ampicillin and amoxicillin has been worked out. This solution was prepared by dissolving 0.0266 g of cerium chloride heptahydrate (Hopkin and Williams) in distilled water and the volume was completed to 100 ml with distilled water in a volumetric flask. This solution was prepared by diluting 50 ml of the above stock cerium(ш) solution to 100 ml in a volumetric flask with distilled water. It was prepared as described (Herkinson, 1965) by dissolving 2.2 g NaCl, 9.7 g MgCl2.6H2O, 3.7 g Na2SO4, 1 g CaCl2, 0.65 g KCl, 0.17 g NaHCO3 and 0.023 g H3BO3 in about 500 ml of distilled water, the resulted solution diluted to 1 L with distilled water in a volumetric flask
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