On-line coated columns for the spectrophotometric determination of metals by continuous flow analysis

The immobilization of xylenol orange, 1-(2ʹ-pyridylazo)-2-naphthol and (p-sulfophenylazo)-2ʹ-sulfo-4ʹ-nitrodiazoa-minobenzene disodium salt (Cadion) on reversed-phase silica (C16, C8, phenyl, C1, CN) and capillary tubes with a hydrophobic inner surface (C6, C-phenyl, C1) in the flow were studied. The flow system including a microcolumn or a capillary tube for the determination of metal ions is suggested. Its versatility and flexibility is provided by on-line coating of the sorbents or inner surface of the capillary tubes. The procedures for the flow spectrophotometric determination of Cd, Co, Cu and Fe(III) in the range 8 × 10−8 −3 × 10−5 M with on-line preconcentration are suggested. The preconcentration factors are up to 9 for the microcolumns and up to 19 for the capillary tubes. The throughput of the system is 19 samples per hour. The method of simultaneous determination of two metals in the mixture (Cu(II) and Co(II), Co(II) and Fe(III), Fe(III) and Zn, Mn(II) and Pb(II)) in the range 1 × 10−6 −7 × 10−5 M at 30–60 samples per hour is developed.