A passive sampler (Chemcatcher) consisting of a 47 mm Ernpore (TM) chelating disk (CHE) with iminodiacetic groups as the receiving phase overlaid with a diffusion membrane was developed and calibrated for the monitoring of Hg in water. Three different diffusion membranes including cellulose acetate (CA), polyethersul phone (PS) and cellulose dialysis membrane (D) were tested. The best performance was obtained with the CHE-PS tandem. The effective sampling rate of the device (R-s, Lday(-1)) is defined as the equivalent Volume of water extracted per unit time, and is analyte specific and can be determined experimentally in a flow-through tank. Effects of water temperature and turbulence on the uptake rate of Hg were assessed tinder controlled laboratory conditions. Sampling rates were in the range of 0.029-0.091 Lday(-1), An increase in sampling rate with turbulence was demonstrated The detection limit. of the sampler obtained in flowing waters ranged between 2.2 and 2.9 ng L-1 Hg The performance of. Chemcatcher was tested alongside spot water sampling in a 14-day field deployment at two locations on the Valdeazogues River, Almaden, Spain. In general, the Hg concentration estimated by the Chemcatcher was lower than that found in spot water samples collected over the same period. This may be explained by the behaviour of this sampler that measures only the labile fraction or Hg in water, and this will exclude some species. However, Chemcatcher preconcentrates Hg allowing its determination in some places where its concentration is below the detection limit of spot sampling. (C) 2008 Elsevier B.V. All rights reserved.