A Comparison of Different Ways of Sample Preparation for the Determination of Phthalic Acid Esters in Water and Plant Matrices

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Abstract
Different methods for the isolation of phthalates from water were tested and compared with the aim of evaluating the risk of secondary contamination of sample and to reach good values of recovery for six tested esters (i.e. dimethyl-, diethyl-, di-n-butyl-, benzylbutyl-, bis(2-ethylhexyl)- and di-n-octyl phthalates). Classic liquid-liquid extraction with hexane gave good recoveries for all six esters (70 - 100%, spiking level 20 μg/1), but the increased relative standard deviations document problems with cross contamination. Micro extraction with iso-octane is suitable for the determination of benzylbutyl-, bis(2-ethylhexyl)- and di-n-octyl phthalates even at low levels of contamination (1 μg/1) and also for di-n-butyl phthalate at higher levels (tens of μg/1). The detection limits for these esters ranged from 0.01 to 0.05 μg/1. The recovery of more polar phthalates (dimethyl-, diethyl phthalate) is very low. Solid phase extraction on octadecyl reverse phase with ethyl acetate as elution solvent was chosen from a variety of tested systems and can be successfully used for the determination of dimethyl-, diethyl, di-n-butyl- and benzylbutyl phthalates (recoveries 72 - 95%, spiking level 20 μg/1). However, recoveries of bis(2-ethylhexyl)- and di-n-octyl phthalate were not higher than 30%. Detection limits ranged from 0.05 to 0.10 μg/1. A method for the determination of phthalates in lettuce, using either alumina adsorption column chromatography or Florisil solid phase extraction as a clean-up step, was developed. Recoveries of all phthalates ranged from 60 to 110% (spiking level 1 mg/kg) and detection limits from 0.01 to 0.05 mg/kg. GC-ECD or GC-MS were used for the identification and quantification of analytes.