Determination of 4-nonylphenol and 4-tert.-octylphenol in water samples by stir bar sorptive extraction and thermal desorption–gas chromatography–mass spectrometry

A simple and highly sensitive method called thermal desorption (TD)–gas chromatography–mass spectrometry (GC–MS), which is used for the determination of trace amounts of 4-nonylphenol (NP) and 4-tert.-octylphenol (OP) in water samples, is described. NP and OP in samples are extracted from water samples and concentrated by the stir bar sorptive extraction (SBSE) technique. A stir bar coated with polydimethylsiloxane (PDMS) is added to a 2.0 ml water sample and stirring is carried out for 60 min at room temperature (25 °C) in a headspace vial. Then the extract is high sensitively analyzed by TD–GC–MS without any derivatization step. The optimum SBSE conditions are realized at an extraction time of 60 min. The detection limits are 0.02 ng ml^-1 for NP and 0.002 ng ml^-1 for OP. The method shows good linearity over the concentration range of 0.1–10 ng ml^-1 for NP and 0.01–10 ng ml^-1 for OP, and the correlation coefficients are higher than 0.999. The average recoveries of NP and OP are higher than 97% (R.S.D.: 3.6–6.2%) with correction using the added surrogate standards, 4-(1-methyl) octylphenol-d5 and deuterium 4-tert.-octylphenol. This simple, accurate, sensitive and selective analytical method may be used in the determination of trace amounts of NP and OP in tap and river water samples.