Determination of phthalic monoesters in aqueous and urine samples by solid-phase microextraction-diazomethane on-fibre derivatization-gas chromatography-mass spectrometry

A solvent-free analytical methodology for the determination of phthalic monoesters (MPs) with diazomethane on-fibre derivatization using solid-phase microextraction-gas chromatography-mass spectrometry (SPME-DOFD-GC-MS) was developed. Among the different SPME fibres evaluated, the polydimethylsiloxane/divinylbenzene (PDMS/DVB) proved to be the most suitable for the determination of four MPs. The diazomethane on-fibre derivatization (DOFD) procedure was improved, avoiding diethyl ether as solvent. Equilibrium conditions were reached (15 min) and K'(MP) values were calculated. Under optimum MP extraction conditions (e.g. direct immersion, 4 mL of sample, 25degreesC extraction temperature, stirring at 1100 rpm, 20 min extraction time, 10 min derivatization reaction, and pH = 1.5), trace level concentrations of MPs (0.3-8.6 ng/mL) were detected, allowing the simultaneous determination of phthalic diesters (DPs). The overall SPME-GC-MS precision was improved by using four deuterated internal standards. The developed analytical methodology was applied to different environmental water matrices and human urine samples at MP concentrations ranging from 0.1-538 ng/mL. The developed analytical procedure is robust (50 analyses with the same fibre), rapid (40 min), and of low cost, improving the conventional analysis methods in terms of analysis time, background levels, and cost.