A novel droplet sensor based on liquid-phase microextraction for on-line aluminum analysis

Abstract

A new droplet sensor based on liquid-phase microextraction and fluorescence detection has been developed. This droplet sensor employs a laboratory-made T-tube with a groove as the optical cell, a simple and cheap light-emitting diode (LED) as the excitation source, and a photomultiplier tube as the photodetector. The performance of the droplet sensor is illustrated with the determination of aluminum (Al). A small drop (40 μL) of a water-immiscible organic solvent (chloroform) containing 8-hydroxyquinoline (HQN) is positioned in the groove of the T-tube and is in contact with a flowing stream of Al(III) solution. Al(III) ion in the aqueous solution is extracted as aluminum oxinate into the chloroform droplet, resulting in the increase in fluorescence of the organic droplet. The droplet sensor displays a wide linear range (50–800 μg L⁻¹) for Al(III) at pH 5.5 and the detection limit is 7.6 μg L⁻¹ (S/N = 3). The distinct advantage of our proposed droplet sensor is that it enables both in situ enrichment and on-line determination of Al(III). By virtue of these valuable features such as low cost, convenience and miniaturization, the droplet sensor is anticipated to have great potential for trace level detection of other metal compounds.