Water Framework Directive watch list method : analysis of 17ß-estradiol and estrone : validation report, according to ISO 17025 requirements

Validation of an analytical method is a necessary step in controlling the quality of quantitative analysis. Method validation is an established process which provides documentary evidence that a system fulfils its pre-defined specification, or shows that an analytical method is acceptable for its intended purpose. The purpose of the present study was to validate an SPE-LC-MS/MS method for the determination of 17b-estradiol and estrone in surface water samples according to the requirements laid down in ISO 17025. The calibration curves, working ranges, recoveries, detection and quantification limits, trueness as well as repeatability were determined. The uncertainty budget was estimated following a top-down approach based on in-house validation data. For 17ß-estradiol, the expanded relative uncertainty was estimated as 16 and 15% at low and high concentration levels respectively, based on 15 replicate measurements on 5 days, and as 50 and 44% for a single measurement performed on a single day. For estrone, the expanded relative uncertainty was estimated as 13 and 12% at low and high concentration levels respectively, based on 15 replicate measurements on 5 days, and as 42 and 38% for a single measurement performed on a single day.