Analytical Sciences

Determination of Cobalt in Natural Water as a 2-(5-Bromo-2-pyridylazo)-5-[N-propyl-N-(3-sulfopropyl)amino]phenol Chelate by On-Line Preconcentration HPLC with Column-Switching Technique

Nobuo UEHARA, Kazuhiro FUKUDA and Yoshio SHIJO

Department of Applied Chemistry, Faculty of Engineering, Utsunomiya University, Ishii-cho, Utsunomiya 321-8585, Japan

2-(5-Bromo-2-pyridylazo)-5-[N-propyl-N-(3-sulfopropyl)amino]phenol (5-Br-PAPS) was used as a precolumn chelating agent for the determination of cobalt in natural water. Co(III)- 5-Br-PAPS chelate was preconcentrated with the concen-tration column (50 mm´´.6 mm i.d.) packed with C18-silica gel sorbent by mean of a column-switching technique. The preconcentrated Co(III) chelate was flushed with the mobile phase by manual action of a switching valve. Then, it was separated by the reversed-phase analytical column. The thermodynamically stable and kinetically inert Co(III) chelate was detected without decomposition using the eluent containing no chelating agent. One cubic centimeter of injection enabled detection of 4.0´±0 -11 mol dm -3 of Co(II) with on-line preconcentration. The method was applied to natural waters. (Keywords: 2-(5-Bromo-2-pyridylazo)-5-[N-propyl-N-(3-sulfopropyl)amino]phenol, HPLC, on-line preconcentration, cobalt, natural water)

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