Assessment of recharge to aquifers

The present invention provides an analytical rotor which holds a fluid in a chamber, typically to allow mixing with a reagent, and transfers the fluid to a receiving chamber in the rotor. The rotor comprises a holding chamber having an single exit duct and a receiving chamber connected to the holding chamber through the exit duct. The exit duct prevents flow at a first rotational speed and allows flow at a second, higher rotational speed. The exit duct may include a capillary passage in which capillary forces prevent flow until the rotational speed is increased. Alternatively, the exit duct may include a siphon.