FIA operates by injecting a precisely measured sample volume into a flowing carrier stream where chemical/enzymatic reactions occur in a plug-flow reactor coil. A detector (photometric, amperometric, or biosensor) measures the reaction product. Key advantages: high automation, reproducibility (~99%), ability to handle complex matrices via dilution, and rapid analysis (<1 min per sample). It interfaces with the fermenter via cross-flow filters, avoiding sterilisation problems.