A one-drop solvent concentration method with a compact evaporator could be used for HPLC analysis to determinate trace levels of Ni(II), Co(II) and Cu(II) ions in an aqueous solution after complexation with sodium diethyldithiocarbamate (DDTC). The ethyl acetate phase, in which metal complexes were extracted by solvent extraction, was transferred to a centrifuge tube, and was added to a micro volume of dimethyl sulfoxide (DMSO). Successful preconcentration of metal complexes into the DMSO phase was accomplished by removing ethyl acetate with a compact evaporator in a water bath (40°C). A four hundred-fold concentration was achieved within 15 min. A portion of the residual DMSO phase was used for a determination by HPLC. The proposed analysis showed both high reproducibility and high sensitivity. The detection limits (3σ) for Ni(II), Co(II) and Cu(II) ions reached at 8.7 × 10−8 M, 6.0 × 10−8 M and 2.0 × 10−8 M, respectively. The relative standard deviation (n = 5) at 5.0 × 10−7 M was 4.2%, 2.0% and 1.0%, respectively.
