Report No DWI0796

Feb 1998

Two methods to determine 17b-oestradiol and 17a-ethinyl oestradiol (as free steroids) in waters were separately developed by the CEFAS laboratory at Burnham-on-Crouch and WRc in 1996 and 1997 respectively. The method produced by CEFAS, involving solid phase extraction, a clean-up step and GCMS (gas chromatography-mass spectrometry) analysis, was designed to determine these three compounds in sewage effluents and river waters, but its performance had not been assessed. WRc developed a method for drinking waters. This involved solid phase extraction, derivatisation, and analysis by GCMS/MS. Performance testing demonstrated that the detection limits for oestrone and 17b-oestradiol were 0.2 ng/l, and 0.4 ng/l for ethinyl oestradiol.

The Drinking Water Inspectorate invited tenders to unify the existing analytical methodology and to undertake limited performance testing using the chosen method. The proposal submitted by WRc, in which it was proposed that both WRc and CEFAS should be involved, was accepted and work commenced in August 1997. During initial discussions it was decided to attempt to modify the method developed by WRc, by incorporating a clean-up step following the derivatisation of the steroids. This was designed to remove excess derivatising agent and by-products which were thought to be responsible for problems during the GC stage of the GCMS/MS analysis. Following experimental work both CEFAS and WRc concluded that there was no advantage to be gained from the clean-up steps that had been investigated and it was decided to proceed to performance test the WRc GCMS/MS method with river waters.

The results of the performance testing suggest that the limits of detection for the three steroids of interest in river waters are about 0.4 - 0.6 ng/l, with both laboratories reporting similar results. If these limits of detection are acceptable, more comprehensive performance testing (e.g. to the criteria currently accepted by the Standing Committee of Analysts) should be undertaken. The analytical method has been written in "Blue Book" format in the Appendix to this report.

A preliminary investigation of the stability of oestrone, 17b-oestradiol and 17a-ethinyl oestradiol in river waters, at a spiking level of about 10 ng /l, suggests that there is some interconversion of oestrone and 17b -oestradiol within less than ten days, and that within twenty days all of these compounds are significantly degraded.

Copies of this report may be available as an Acrobat pdf download under the 'Find Completed Research' heading on the DWI website.