Carter et al. (2025) present a FDA method validation for simultaneous determination of methylmercury (MeHg) and total mercury (tHg) in finfish using a combination of thermal decomposition amalgamation atomic absorption spectrometry (TDA-AAS) and salting-out assisted liquid-liquid extraction (SALLE). The validation includes 10 certified reference materials across multiple finfish species, establishing this as a regulatory-quality method for fish mercury speciation.
Key numbers
LOD (TDA-AAS): 3.8 ng/g (3.8 ppb wet weight) for mercury in finfish.
LOQ (TDA-AAS): 27 ng/g (27 ppb wet weight) for mercury in finfish.
Method: validated against 10 certified reference materials (CRMs), establishing accuracy and precision across the concentration range relevant to fish mercury regulations. The combination of TDA-AAS and SALLE provides both total Hg (by TDA) and MeHg (by SALLE extraction followed by AAS or GC-AAS).
US Government Work — public domain, no copyright restrictions.
Methods (brief)
TDA-AAS: solid or liquid sample directly thermally decomposed; mercury amalgamated and detected by AAS. Established FDA method platform. SALLE: salting-out assisted liquid-liquid extraction for MeHg speciation. 10 CRMs validated. Finfish muscle tissue, wet weight basis. High analytical credibility: FDA-validated, CRM-confirmed, peer-reviewed publication.
This is one of the methodologically most important papers in this batch because it provides a validated FDA-level method for the iAs/MeHg distinction in the fish matrix and establishes concrete LOD/LOQ values against certified reference materials.
Implications
Certification: HMT&C tracks MeHg and tHg as separate analytes. This FDA method establishes the LOQ for fish-based products at 27 ppb tHg and 27 ppb MeHg; any HMT&C certification limit for fish-based products must be at or above these LOQs to be analytically enforceable.
Courses: Key reference for the testing methods course module on mercury speciation in fish. The LOD/LOQ values from this FDA validation are authoritative reference points for what is analytically achievable in fish matrices.
App: The 3.8 ppb LOD and 27 ppb LOQ for fish matrices are important inputs for the app’s “below LOQ” data handling logic.