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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 11 Issue 3 (2006) pp 187-189

Unconventional Liquid–Liquid Extraction in Undergraduate Laboratories: Cloud-Point Separation and Preconcentration

Márcia A. M. S. Veiga, Fábio R. P. Rocha*

Instituto de Química, Universidade de São Paulo, PO Box 26077, 05513-970, São Paulo, SP, Brazil, (F.R.P. Rocha)
Received November 17, 2005. Accepted March 17, 2006.

Published online: 25 May 2006

Abstract. A laboratory exercise aiming to introduce a green liquid–liquid extraction approach for undergraduate laboratories is described. It is based on the cloud-point phenomenon, a phase separation exhibited by nonionic surfactant aqueous solutions when some conditions, such as pressure or temperature, are modified. The micelle aggregates separate in a small-volume surfactant-rich phase, containing hydrophobic species, which can be extracted and concentrated. In this experiment, the cobalt(II) complex formed with the azo-reagent 1-(2-thiazolylazo)-2-naphthol is extracted with Triton X-114. The cloud-point is induced by heating above 25 °C. The whole process can be visually observed and quantitative measurements can be carried out by UV–vis spectrophotometry. Experimental variations and some didactical aspects that can be emphasized are also discussed.

Key Words: analytical chemistry; green chemistry; liquid-liquid extraction; cloud-point; UV–vis spectrophotometry

(*) Corresponding author. (E-mail:

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Issue date: June 1, 2006

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