Abstract: A small liquid sample (24) to be tested is contained within an annulus (18) on the upper surface (14) of a substrate (12). In one embodiment, a reagent diffuses into the sample through a membrane (28) in a junction hole (26), the junction hole connecting upper (14) and lower (16) surfaces of the substrate. Optical measuring equipment (70, 72) detects a measurable change in an optical property of the sample. In an alternate embodiment, a flow of gas (30), directed at the small liquid sample (24), causes the sample to flow in a controlled manner over the surface of an electrode (20), disposed on the substrate surface (14). In another alternate embodiment, a special averaging electrode (20) is disposed in a non-homogeneous sample (24). Highly reproducible and accurate hydrodynamic electrochemical studies and analyses of microliter size samples are thus achievable, without the need for moving mechanical parts.