A project was undertaken to develop mussel reference materials that were ce
rtified for their mass fractions of saxitoxin and decarbamoyl-saxitoxin. Fi
fteen laboratories from various European countries participated. Three of t
hese had major responsibility for substantial parts of the work and overall
coordination of the project. The project involved 4 main activities: (1) p
rocurement and characterization of calibrants; (2) improvement of analytica
l methodology; (3) preparation of reference materials, including homogeneit
y and stability studies; (4) 2 interlaboratory studies and a certification
exercise. The joint activities resulted in 3 homogeneous and stable referen
ce materials: 2 lyophilized mussel materials with and without naturally inc
urred paralytic shellfish poisoning (PSP) toxins, and a saxitoxin enrichmen
t solution. The reference materials were certified with respect to their sa
xitoxin and decarbamoyl-saxitoxin content. The lyophilized mussel material
with PSP toxins (CRM 542) contained <0.07 mg saxitoxin.2HCl/kg and 1.59 +/-
0.20 mg decarbamoyl-saxitoxin.2HCl/kg. The lyophilized mussel material with
out PSP toxins (CRM 543) contained <0.07 mg saxitoxin.2HCl/kg and <0.04 mg
decarbamoyl-saxitoxin.2HCl/kg. The certified value of the saxitoxin mass fr
action in the saxitoxin enrichment solution (CRM 663) was 9.8 +/-1.2 mug/g.