METHOD FOR THE DETERMINATION OF SOME SELECTED STEROID HORMONES AND BISPHENOL A IN WATER AT LOW NG/L LEVEL BY ON-LINE SOLID-PHASE EXTRACTION COMBINED WITH LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY

Abstract

A sensitive analytical method based on automatic on-line Solid-Phase Extraction (SPE) combined with Liquid Chromatography-Tandem Mass Spectrometry (LC-ESI-MS-MS) has been developed for the determination of six Endocrine-Disrupting Compounds (EDC's): 17-alpha-estradiol, 17-alpha-ethynylestradiol, 17-beta-estradiol, bisphenol A, Estriol and Estrone in water samples. In order to enhance the sensitivity for these analytes, post column addition of different bases such as ammonia and 1,8-diazabicyclo(5,4,0)undec-7en (DBU) was evaluated. The post column addition of base is proposed here to raise effluent pH, helping in the ionization process of the compounds. The use of ammonium hydroxide diluted in methanol-acetonitrile mixture, proved to be the most efficient post column reagent for enhancing the MS signal. This strategy permitted direct determination of the six compounds at low ng/L levels. For the application to real water samples, an extraction and preconcentration step using SPE was carried out with cross-linked styrene-divinylbenzene polymer (PLPR-s) material. The recovery for all six compounds was satisfactory percentage (80-110%). The limits of quantification are between 1.0 and 2.0 ng/L. Application of the whole method, SPE-LC-ESI-MS-MS, to nature waters permitted low nanogram-per-liter determination of all six compounds.