FLOW-INJECTION ANALYSIS BASED ON A MEMBRANE SEPARATION MODULE AND A BULK ACOUSTIC-WAVE IMPEDANCE SENSOR - DETERMINATION OF THE VOLATILE ACIDITY OF FERMENTATION PRODUCTS

A novel flow-injection analysis (FIA) system has been developed for th e rapid determination of the volatile acidity of some fermentation pro ducts like vinegars and juices. The proposed method is based on the di ffusion of volatile acids, mainly acetic acid, across a PTFE gas-perme able membrane from an acid stream into an alkaline stream, and the aci ds trapped in the acceptor solution are determined online by a bulk ac oustic wave impedance sensor based on changes in the conductivity of t he solution. It exhibited a linear frequency response up to 10 mmol L- 1 acetic acid with a detection limit of 50 mu mol.L-1. and the precisi on was better than 1% (RSD) at a through-put of 72 h(-1). The effects of operating voltage for the detector, cell constant of the electrode, composition of acceptor stream, flow rates and temperature on the FIA performance were also investigated.