924 (2001) 407–414 Journal of Chromatography A, www.elsevier.com / locate / chroma Liquid–liquid–liquid microextraction of nitrophenols with a hollow fiber membrane prior to capillary liquid chromatography * Lingyan Zhu, Liang Zhu, Hian Kee Lee Department of Chemistry, National University of Singapore,3 Science Drive 3, Singapore 117543, Singapore Abstract A simple liquid–liquid–liquid microextraction device utilizing a 2 cm30.6 mm I.D. hollow fiber membrane was used to preconcentrate nitrophenols from water sample prior to capillary liquid chromatography (cLC) analysis. The extraction procedure was induced by the pH difference inside and outside the hollow fiber. The donor phase outside the hollow fiber was adjusted to pH|1 with HCl; the acceptor phase was NaOH solution used at various concentrations. Organic solvent was immobilized into the pores of the hollow fiber. With stirring, the neutral nitrophenols outside the fiber were extracted into the organic solvent, then back extracted into 2 ml of basic acceptor solution inside the fiber. The acceptor phase was then withdrawn into a microsyringe and injected into the cLC system directly. This technique used a low-cost disposable extraction ‘‘device’’ and is very convenient to operate. Up to 380-fold enrichment of analytes could be achieved. This procedure could also serve as a sample clean-up step because large molecules and basic compounds were not extracted into the acceptor phase. The RSD ( n56) was less than 6.2%, while the linear calibration range was from 1 to 200 mg/ml with r.0.998. The procedure was applied to the analysis of seawater.  2001 Elsevier Science B.V. All rights reserved. Keywords: Liquid–liquid–liquid microextraction; Extraction methods; Hollow-fiber membranes; Water analysis; En- vironmental analysis; Nitrophenols 1. Introduction are environmentally of particular interest and con- cern. Gas chromatography (GC) and high-perform- Phenols and substituted phenols are important ance liquid chromatography (HPLC) are the most pollutants in water because of their wide use in many common analytical techniques used for the determi- industrial processes such as the manufacture of nation of phenols [5–8]. In GC, derivatization is plastics, dyes, drugs, antioxidants and pesticides [1]. needed to analyze phenols in order to avoid peak Nitrophenols are formed photochemically in the tailing [6,7,9]. Compared with GC, HPLC is a good atmosphere from vehicle exhausts [2]. They are very alternative technique, in which isocratic or gradient toxic and have a diverse effect on the taste and odor elution can be used to separate these compounds. of drinking water at low concentrations [3,4], so they Capillary liquid chromatography (cLC) has as- sumed greater applicability in recent years, and has been used for environmental analysis [10,11] due to its high resolution, small sample volume requirement and comparatively better analyte detectability than *Corresponding author. Tel.: 165-874-2995; fax: 165-779- conventional LC. San Andres et al. [12] used cLC to 1691. E-mail address: chmleehk@nus.edu.sg (H.K. Lee). analyze phenols in water. A preconcentration step is 0021-9673 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0021-9673(01)00906-2 http://www.paper.edu.cn