COLLABORATIVE SAMPLING ERROR ASSESSMENT OF TRACE-METAL DETERMINATION IN SEAWATER

An international intercomparison of sampling devices was conducted to assess different collection procedures in gathering seawater samples f rom the Mediterranean for determination of Pb, Cd and Cu. Four kinds o f samplers (Go-Flo, Niskin, van Dorn and Ruttner) with capacities of b etween 2 and 30 1 were used. The 20 1, Teflon-coated Go-Flo sampler wa s considered as the reference. Samples were collected at 20 and 50 m d epth at four sites. Measurements were carried out by Differential Puls e Anodic Stripping Voltammetry (DPASV) both on board, immediately afte r collection, and on stored samples in the reference laboratory. Analy tical quality control was guaranteed by the reference laboratory. The mean concentration values obtained using the reference sampler were (i n nM unit): 0.34 (SD 0.04) for Pb, 0.058 (SD 0.012) for Cd and 3.7 (SD 0.6) for Cu, in agreement with recent, reliable literature data. Resu lts obtained with other samplers showed that they became progressively cleaner during use (and the continuous washing programme) with concen tration values tending to those obtained with the reference sampler. B etter results were obtained for high-capacity samplers, indicating tha t the volume of sampler (or rather the ratio between the volume and th e contact surface) can have a considerable effect on sample contaminat ion.