Continuous chemical monitoring with osmotically pumped water samplers: OsmoSampler design and applications

Long-term osmotically pumped fluid samplers, or OsmoSamplers, were developed to reliably and autonomously collect continuous small-volume water samples for monitoring aqueous environments in remote locations for up to several years. OsmoSamplers provide sequential milliliter-size samples that, when analyzed, yield high-resolution time-series for a wide range of dissolved components. These instruments fill an important niche that has not been addressed by automated samplers or in situ analyzers. OsmoSamplers can be customized for flow rate and duration for addressing numerous scientific questions. The samplers consist of an osmotic pump that continuously pulls fluid sample into a long small-bore tube. They are thus extremely simple, reliable, and require neither electrical power nor moving parts. Upon recovery, fluid samples are extracted from subsections of the sample tubing, where each subsection integrates a discrete time interval. The time-stamped subsamples are then analyzed for chemical species of interest. Sample smearing due to static and dynamic diffusion and mixing is kept to a minimum by the use of small-bore tubing (0.5 to 1.2 mm inside diameter) and low flow rates (0.1 to 12 mL d−1). Theory and laboratory experiments show that sample smearing is not significantly greater than that calculated from static diffusion alone. OsmoSamplers have been tested in the laboratory and deployed at sea. Results from laboratory tests and field deployments illustrate initial results and potential applications.