Analytical Sciences

Enhanced Retention of Chelating Reagents in Octadecylsilyl Silica Phase by Interaction with Residual Silanol Groups in Solid Phase Extraction of Divalent Metal Ions

Satoshi OHMURO,* Kan FUJII,* Takashi YASUI,* Kazutake TAKADA,* Akio YUCHI,* and Hisao KOKUSEN**

*Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan
**Department of Chemistry, Tokyo Gakugei University, Nukui-kita-machi, Koganei, Tokyo 184-8501, Japan

Solid-phase extraction (SPE) of divalent metal ions with a lipophilic and potentially divalent hexadentate chelating reagent (H₂L), with which octadecylsilyl silica (ODS), was impregnated with was studied to gain more insight into and develop the potential of this methodology. This is the first time to demonstrate that this reagent as well as other common nitrogen-containing reagents were retained both by adsorption due to hydrogen bonding between nitrogen atoms of the reagent and residual silanol groups in the ODS phase and by simple distribution into the hydrophobic space. An appreciably large amount of this reagent could be retained by the adsorption mechanism even with a relatively thin loading solution. The divalent metal ions of Mn²⁺, Co²⁺ and Zn²⁺ were extracted as 1:1 neutral complexes ([ML]), while Ni²⁺ and Cu²⁺ as ion-pairs of 1:1 cationic complex ([MHL]⁺) with anion in SPE with H₂L. The extractability and selectivity were substantially the same as that in liquid–liquid extraction.

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