A method for determining the diffusion of one or more components, the method includes the steps of (i) providing a component fluid flow having one or more components; (ii) providing a blank fluid flow; (iii) bringing the flow (i) into contact with the flow (ii) in a large cross section channel, thereby to generate two laminar flows; (iv) permitting the laminar flows generated in (iii) to flow from the large cross section channel into a small cross section channel; measuring the lateral diffusion of the one or more components from the component flow into the blank fluid flow in the small cross section channel. Also provided is a diffusion method having the steps of measuring the lateral diffusion of the one or more components from the component flow into the blank fluid flow at a plurality of diffusion times.