Abstract :
Three forms of liquid¯liquid extraction in flow-injection systems are compared and applied to the fluorimetric determination of aluminium after its extraction in chloroform as aluminium oxinate. In the first form, conventional phase segmentation and separation are used. Concentrations of aluminium higher than 6 mug l-1 can be detected with a linear application range between 20 and 800 mug l-1, a R.S.D. of 2.8% (50 mug l-1, n=10) and a sampling frequency of 20 h-1. The second form includes phase segmentation, but fluorescence is measured without phase separation. In this mode, aluminium is detected at concentrations higher than 2 mug l-1 with a linear application range of 10¯800 mug l-1, a R.S.D. of 2.3% (50 mug l-1, n=10) and a sampling frequency of 30 h-1. In the third form, a single segment of organic solution is injected into the aqueous stream and fluorescence is measured without phase separation too. Using this mode, concentrations of aluminium higher than 0.2 mug l-1 can be detected, with a linear application range between 2 and 120 mug l-1, a R.S.D. of 4.9% (50 mug l-1, n=10) and a sampling frequency of 60 h-1. All the three forms are applied to the analysis of aluminium in drinking, river and waste water. Under the proposed working conditions, only Fe(III) interferes but this interference is avoided when a mixture of hydroxylamine and ophenanthroline is added.
