The invention relates to a method and an apparatus for handling small quantities of fluids useful, for example, in measuring the gas and/or liquid sorption and desorption properties of substances such as hydrogen sorption by solid or liquid hydrogen storage materials. In one embodiment, low-volume rotary valves are used to dose samples in a sample holder. In another embodiment, a rotary valve is used as a dosing/bypass valve to both condition and measure samples. The invention also relates to an actuator for a rotary valve that has a manual override feature.