Determination of cobalt(II) with 3-mercapto-1,5-diphenyl formazan by means of reversed-phase partition high performance liquid chromatography.

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Abstract
The determination of cobalt(II) with 3-mercapto-1, 5-diphenyl formazan (dithizone) by a reversed-phase partition high performance liquid chromatography is described. Co(HDz)3 was separated from a mixture of Ni(HDz)2, Zn(HDz)2, Pb(HDz)2 and Cd(HDz)2 on a stainless steel column packed with Shimadzu Zorbax ODS by the use of methanol-water as a mobile phase. Co(HDz)3was first eluted to give a sharp elution peak, and the other complexes were eluted with almost the same retention time. The recommended procedure for the determination of cobalt(II) is as follows: A 10 ml of the sample solution containing cobalt(II), other metal ions and 100 mg of disodium tartrate should be shaken for 20 min with 10 ml of 5.00 × 10-3 mol dm-3 dithizone in chloroform at pH 8.5. An excess of dithizone in the extract can be removed by washing the extract with an ammonia-water mixture. A 10μl of the extract can be injected into the column by means of a micro syringe. Cobalt(II) can be determined in the range of 5.2 to 30.0 ng with the peak area calibration curve obtained at 550 nm in the presence of 24.2 ng nickel(II), 18.8 ng zinc(II), 52.6 ng lead(II) and 5.2 ng cadmium(II) using 85%(v/v) methanol-water at the flow rate of 1.0 ml/min within a relative error of + 4%. The analysis time was about 25 min.

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