A sample (analyte) is injected into a flowing carrier solution stream that is forced by a peristaltic pump. The injection of the sample is done under controlled dispersion in known volumes. The carrier solution and sample then meet at mixing points with reagents and react. The reaction time is controlled by a pump and reaction coil. The reaction product then flows through a detector. Most often, the detector is a spectrophotometer as the reactions usually produce a colored product. One can then determine the amount of an unknown material in the sample as it is proportional to the absorption spectrum given by the spectrophotometer. After moving through the detector, the sample then flows to waste.
Detail of sample dispersion
When a sample is injected into the carrier stream it has the rectangular flow. As the sample is carried through the mixing and reaction zone, the width of the flow profile increases as the sample disperses into the carrier stream. Dispersion results from two processes: convection due to the flow of the carrier stream and diffusion due to a concentration gradient between the sample and the carrier stream. Convection of the sample occurs by laminar flow, in which the linear velocity of the sample at the tube's walls is zero, while the sample at the center of the tube moves with a linear velocity twice that of the carrier stream. The result is the parabolic flow profile, before the sample passes through a detector to a waste container.