Absorption Spectra of the 4f Electron Transitions of the Praseodymium Complex with 1-Cyclopropyl-6-fluoro-1,4-dihydro-7-(4-ethyl-1-piperazinyl)-4-oxo-3-quinoline Carboxylic Acid Hydrochloride and Its Analytical Application

Abstract

A number of metallochromic reagents have been described for the spectrophotometric determination of praseodymium. [1][2][3][4][5] None of them are specific for praseodymium in the presence of other rare earths because of a considerable overlap between their broad absorption spectra. However, there has long been interest in the determination of individual elements based on the absorption bands of their 4f electron transitions. [6][7][8][9][10][11] In recent papers, the third/second derivative spectrophotometric determination of complexes formed by some rare earths with 8-hydroxylquinoline and its derivative, 12-15 β-diketones 16,17 and inorganic salts 18,19 were investigated, which can be utilized for the determination of neodymium, holmium and erbium. However, applications to praseodymium are rare.1-Cyclopropyl-6-fluoro-1,4-dihydro-7-(4-ethyl-1-piperazinyl)-4-oxo-3-quinoline carboxylic acid hydrochloride (NNFX) is the third representative of antibacterial medicine, namely the quinolone group, used extensively in clinical treatment with higher potential and a broad antibacterial spectrum as well as fewer side effect. However, its utilization as a reagent for the determination of rare earth elements has not been reported. In the present work, the absorption spectra of the praseodymium complex with NNFX was investigated by applying both normal and derivative spectrophotometric methods. On this basis, a method was developed for the direct determination of praseodymium in rare earth mixtures. The analytical results obtained are satisfactory. Experimental ApparatusA Shimadzu UV-3000 double-beam spectrophotometer (Kyoto, Japan) with 4.0-cm cells was used. The pH-values of the solutions were measured with a pHs-2 meter (Analytical Apparatus Plant, Shanghai, China). Reagents and chemicalsStock lanthanide solutions (0.01 M) were prepared by dissolving an appropriate amount of pure oxides (Johnson Matthey, Royston, Hertfordshire, UK) in hydrochloric acid (1+1), and working solutions were prepared by dilution with water. A solution of 1-cyclopropyl-6-fluoro-1,4-dihydro-7-(4-ethyl-1-piperazinyl)-4-oxo-3-quinoline carboxylic acid hydrochloride (NNFX, 0.05 M) was prepared by dissolving 1.797 g of NNFX (Zibo Pharmacy Plant, People's Republic of China) in 100 ml of distilled water in a calibrated flask. A buffer solution of pH 6.0 was prepared by dissolving 200 g of hexamethylene tetramine in 500 ml of distilled water, the pH being adjusted with hydrochloric acid (1+1) and diluting to 1000 ml with distilled water.Analytical-reagent grade chemicals were used whenever possible. ProcedureA known volume of a lanthanide solution (containing Pr up to 50 µg) was transferred into a 10 ml calibrated flask; 3.0 ml of 0.05 M NNFX and 4.0 ml of pH 6.0 buffer solutions were added. The mixture was diluted to the mark with distilled water, and after 30 min the third-derivative spectra were recorded against a reagent blank using 4.0-cm cells with a ∆λ of 2.8 nm, a band pass of 1.0 nm and a scan rate = 50 nm min -1 as instrumental parameters. Th...