Simultaneous separation of metal ions and neutral organics by reversed-phase ion-pair liquid chromatography

Mixtures of divalent metal ions and neutral organics (phenols, anilines, polynuclear aromatics) were separated and detected by isocratic high-performance liquid chromatography in one run using standard cation-exchange ion-pairing or ion-interaction reagents (IIRs) and water-methanol-tartrate mobile phases on a C-18 reversed-phase column. The column could be coated with the more hydrophobic (C-18, C-20) IIRs but severe bleeding occurred in mobile phases containing more than 30% methanol. Most work was done with the IIR incorporated in the mobile phase. In eluents containing about 30% methanol the C-8 (octanesulfonate) IIR was most useful: the C-12 (dodecyl sulfate) IIR proved best around 50% methanol; and the C-18 (octadecyl sulfate) IIR was most effective above 70% methanol. IIR concentrations in the 1-10 mM range were used. Detection of organics was carried out at 254 nm. Metal ions were post-column derivatized with 4-(2-pyridylazo)resorcinol downstream from the UV detector and monitored at 510 nm at a second detector. Metal ion retention increased with decreasing pH and methanol concentration and increasing IIR concentration. The presence of the IIR had only a slight effect on organic analyte retention as compared to the same water-methanol mobile phase with no IIR. Both peak area and height were linear with analyte concentration from about 10(-2) to 10(-5) M for both metal ions and organics. (C) 1997 Elsevier Science B.V.