In-vessel extraction using a microtube and its application to the fluorimetric determination of trace lead

Abstract

A new method has been developed for solid-phase extraction using a polypropylene microtube. A relatively large surface area of the tube wall and the agitating motion of the elution solvent in the vortex provide a simple, rapid, and inexpensive method for extracting trace elements in a sample solution of 1 ml. The proposed method has been successfully applied to the fluorimetric determination of trace lead; the ion-pair of the lead complex with 5,6-14,15-dibenzo-4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo (8,8,8) hexacosane (dibenzo-cryptand 2.2.2) and Eosin Y is extracted onto a microtube wall at pH 7.0. The ion-pair is then eluted into 500 μl of ethanol–water (4 + 1). The calibration curve based on the fluorescence of Eosin Y is linear over the concentration range up to 1.5 × 10⁻⁶ mol l⁻¹. The detection limit is 3 × 10⁻⁸ mol l⁻¹ (6 μg l⁻¹). In addition to the stability of the dibenzo-cryptand 2.2.2-lead complex, the charge effect in ion-pair extraction with the divalent counter ion, Eosin Y contributes to the high selectivity for the doubly positively charged lead-dibenzo-cryptand 2.2.2 complex. The proposed method lends itself to great potential use as a field test for trace lead in water samples, which has long been wanted.