ADVANCES IN ION CHROMATOGRAPHY - SPECIATION OF MU-G 1-1 LEVELS OF METALLO-CYANIDES USING ION-INTERACTION CHROMATOGRAPHY

Fe(CN)6(4-), Cu(CN)4(3-), Co(CN)6(3-), Fe(CN)6(3-), Ni(CN)6(3-) and Cr(CN)6(3-) are determined by ion-interaction chromatography using a C18 column and methanol-tetrahydrofuran-10 mM phosphate buffer (pH 7.9) (25 + 1 + 74, v/v/v) containing 5 mM tetrabutylammonium hydroxide as mobile phase, with spectrophotometric detection at 214 nm. Detection limits are in the range 0.01-0.5 mg l-1. In an alternative approach, an automated on-line sample preconcentration technique is used wherein a 2-ml volume of sample containing metallo-cyanides is loaded onto a C18 precolumn which has been equilibrated with the above mobile phase. The bound solutes are then eluted from the precolumn to a C18 analytical column where they are separated using the same mobile phase as employed to equilibrate the precolumn. Detection limits are in the range 0.08-1.58-mu-g l-1 and calibration graphs are linear up to 200-mu-g l-1 The preconcentration step is shown to give quantitative recoveries for all species except Fe(CN)6(4-) and Cu(CN)4(3-). The iron(II) complex does not bind quantitatively to the precolumn, and extensive studies with the copper complex suggested that low recoveries were due to dissociation and ligand-exchange reactions occurring during the chromatographic separation process. Negative interference effects were observed for Cl- and SO42- when present at a level of 250 mg l-1, and UV-absorbing anions such as Br-, SCN-, NO2- and NO3- caused positive interference when present at concentrations as low as 1 mg l-1. The negative interferences could be reduced by diluting the sample and the positive interferences could be eliminated by incorporating an additional step in the preconcentration process, in which UV-absorbing anions bound to the precolumn after sample loading were eluted selectively using an eluent consisting of 10 mM NaCl in phosphate buffer (pH 6.7).