Full method validation for the determination of hexachlorobenzene and hexachlorobutadiene in fish tissue by GC-IDMS

This paper summarizes the validation strategy and the results obtained for the simultaneous determination of hexachlorobenzene (HCB) and hexachlorobutadiene (HCBD) in fish tissue with a maximum of about 10% m/m fat content using a GC-IDMS technique. The method is applicable for the determination of HCB and HCBD at trace levels in different kinds of fish tissue samples in accordance with the requirements of the EU Directive 2008/105/EC establishing Environmental Quality Standard (EQS) levels for biota in aquatic ecosystems (10 ng/g for HCB and 55 ng/g for HCBD). The method validation aimed to assess performance parameters such as linearity, limit of detection/limit of quantification (LOD/LOQ), trueness, selectivity, intermediate precision, repeatability, stability of the extracts and robustness. The validation experiments have been performed by using uncontaminated fish tissue. Trueness was evaluated by using a certified reference material (NIST SRM 1947) (where applicable) and by the standard addition method. Very good linear signal-concentration curves were obtained for both analytes over the whole range of calibration. The repeatability and the intermediate precision of the method, expressed as relative standard deviation (RSD) and calculated at the EQS level, were estimated to be below 3% both for HCB and HCBD. The limits of quantification were 3.7 ng/g for HCB and 15.7 ng/g for HCBD in the fish. An uncertainty budget for the measurement of both HCB and HCBD in fish at about the EQS levels, applying the described method, has been established in the order of 10%. The analytical method and its performance characteristics take into account the requirements of EU Directive 2009/90/EC regarding the establishment of minimum performance criteria for the methods of analysis to be used in the water monitoring activity of the Water Framework Directive. Finally, the validated method was successfully tested on contaminated Silurus glanis from Ebro River (Spain). The method will be used in the homogeneity, stability and interlaboratory comparison studies for the characterization of a new candidate certified reference material.