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The development and evaluation of a new method for the determination of trace transition and rare-earth elements based on the combination of chelation and ion chromatography are described. The new method, chelation ion chromatography (Chelation IC), uses a chelating column to concentrate and separate transition and rare-earth elements from the common alkali and alkaline-earth metals, as well as other matrix components, prior to analysis by ion chromatography. The sample fraction from the chelating column contains only the concentrated analyte ions, thus eliminating interfering matrix components from complex matrices such as seawater and digested biological, botanical, and geological materials. This combination of chelation and ion chromatography provides a technique that makes possible the determination of trace elements in complex matrices that have proven to be difficult or impossible to analyze by ion chromatography or conventional atomic spectroscopy techniques.

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A method for determination of metal ions subsequent to ion chromatographic separatkn has been devlsed. The method Is bared on indirect amperometric detection whereby a decrease In an oxidation current, proportional to the concentration of metal ion, is monitored. In this particular work, an easlly oxldlred band is added postcolumn. Upon complexatbn with the metal ions, the ligand is rendered electroinactlve at the preseleted potentlal. The fact that the ligand Is oxidized at low anodlc potentials results In a selective detection system.The separation of metal species using liquid chromatography and their subsequent detection remains a challenging field of research. Separation may be achieved by using normal-phase (1, 2) or reversed-phase (3-11) chromatography, subsequent to a suitable derivatization process, or ion exchange chromatography (12)(13)(14)(15)(16)(17)(18)(19)(20). In recent times excellent selectivity has been attained by using ion exchange chromatographic procedures wherein the metals are separated as charged complexes (17-20).Spectrophotometric (I-@, electrochemical (&IO), and atomic absorption spectrometry (16, 17) are amongst the methods of detection that have been investigated. Spectrophotometric (W-vis) and electrochemical (EC) detection have attracted most interest since they offer multielement analysis capabilities. These detection methods are usually employed in conjunction with a derivatization step for determination of metals. For UV-vis detection, the purpose of the derivatization is to produce a metal species, usually a complex, with a high extinction coefficient, enabling sensitive detection.Derivatization prior to electrochemical detection may be used to enhance the electrode process as well as to overcome problems associated with the electrochemical reduction of dissolved oxygen.With the above requirements in mind the dithiocarbamate ligand (I shown below) has proven particularly useful as a(1) dil niocar bamate f dtc derivatizing agent for metal ions prior to separation and detection. The most convenient method described achieves derivatization of the metal ions, in situ, by including the ligand in the chromatographic solvent (3)(4)(5)(6)(7)(8)(9)(10)(11). This allows for direct injection of metal ions. Subsequent to in situ derivatization the metal complexes are separated by using reversed-phase chromatography and detected by using either UV-vis or EC detection. The method is limited in that, in some cases, the instability of the metal complexes on-column mitigates against development of a successful analysis procedure. Other major drawbacks of this method are found in the detection stage. To enable rapid in situ formation an excess of dithiocarbamate must be present in the eluent. The free dithiocarbamate ligand absorbs in the UV region of the spectrum (21) causing high backgrounds with UV-vis detection. The free ligand is also oxidized electrochemically at relatively low positive potentials (22) according to the following:and therefore, monitoring of metal oxidation processes that ...