Design of simple and sensitive methods for trace analysis by means of concentration with a membrane filter

Novel techniques of membrane filtration for the enrichment and determinatio n of trace components in water are reviewed from an aspect of downsizing in analytical chemistry. One method is based on the conversion of a component in water to a hydrophobic species by a chemical reaction, and its retentio n on a membrane by a hydrophobic interaction between the species and the me mbrane material. The species retained on the membrane are eluted or dissolv ed together with the membrane in a small volume of solvent and determined b y an appropriate instrumental method, such as spectrophotometry, GF-AAS or ICP-AES. More than a 100-fold enrichment has been easily attainable by this method. Other enrichment/determination approaches without elution and diss olution, by means of reflective spectrophotometry, tristimulus colorimetry and using a transparent membrane filter have exhibited new potentials of th is method from the view point of zero emission-chemistry, in addition to a simple and rapid procedure. Some typical applications of this technique to the preconcentration and determination of trace components in environmental water samples were described. The retention behavior of ion-pairs on a mem brane filter was interpreted by ion-pair solid-phase extraction equilibrium . The effects of functional groups in the ions and solid-phase materials, t he structure of the ions and the organic solvent added to the aqueous phase on the extraction behavior are described.