Journal
ANALYTICA CHIMICA ACTA
Volume 597, Issue 1, Pages 32-40Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.aca.2007.06.021
Keywords
single-drop liquid-phase microextraction; ion-pairing transfer; ethyl chloroformate derivatisation; endocrine disruptors
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A novel in-drop derivatisation liquid-phase microextraction procedure with an ion-pairing agent is developed and optimised for the extraction of endocrine-disrupting chemicals. The ethyl esters of the analytes were rapidly formed in the organic drop and analysed by gas chromatography. The effects of various parameters such as rate and time of agitation, ion-pairing agent and reactant concentration, pH and temperature were studied systematically to optimise the process and bring out the locale of reaction in the organic drop. A study of the mechanistic pathways of the overall procedure is attempted leading to interesting findings and delineating important points of the kinetics and mechanism. A mechanistic model is proposed on the basis of the theory of mass transfer with chemical reaction in two liquid phases. The O-ethoxycarbonyl deriyatisation appears to take place in the bulk organic phase. The system provides insight into the first reported analytical case of single-drop extraction-preconcentration-derivatisation assisted by an ion-pairing transfer and has all of the interesting facets of chemical reaction in which the role of mass transfer comes into picture. The analytical features of the method are acceptable and the overall relative standard deviations of the intra-day repeatability (n = 5) and inter-day reproducibility were < 3.9% and < 5.4%, respectively, for gas chromatography-mass spectrometry analyses and < 4.3% and < 7.1% for gas chromatography-flame ionisation detection analyses. The method was applicable to urine and surface water samples. The LODs ranged between 0.2-1.3 ng mL(-1) and 8.5-26.5 ng mL(-1) for GUMS and GC/FID analyses, respectively. (c) 2007 Elsevier B.V. All rights reserved.
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