CRM-Zero-Mus is a mussel tissue (Mytilus edulis) matrix CRM intended for use as a negative control for the analysis of paralytic shellfish toxins (PST), domoic acid (DA) and its isomers, okadaic acid (OA) and diniphysistoxins (DTX), azaspiracids (AZA), yessotoxins (YTX), pentenotoxins (PTX) and gymnodimine (GYM). CRM-Zero-Mus is not suitable as a negative control for spirolides (SPX) and pinnatoxins (PnTX) because these toxins are present, albeit at very low levels.