DETERMINATION OF COBALT IN NATURAL-WATER AS A IDYLAZO)-5-[N-PROPYL-N-(3-SULFOPROPYL)AMINO]PHENOL CHELATE BY ONLINE PRECONCENTRATION HPLC WITH COLUMN-SWITCHING TECHNIQUE

-2-pyridylazo)-5-[N-propyl-N-(3-sulfopropyl)amino] phenol (5-Br-PAPS) was used as a precolumn chelating agent for the determination of cobal t in natural water. Co(III)-5-Br-PAPS chelate was preconcentrated with the concentration column (50 mmx4.6 mm i.d.) packed with C18-silica g el sorbent by mean of a column-switching technique. The preconcentrate d Co(III) chelate was flushed with the mobile phase by manual action o f a switching valve. Then, it was separated by the reversed-phase anal ytical column. The thermodynamically stable and kinetically inert Co(I II) chelate was detected without decomposition using the eluent contai ning no chelating agent. One cubic centimeter of injection enabled det ection of 4.0 x 10(-11) mol dm(-3) of Co(II) with on-line preconcentra tion. The method was applied to natural waters.