Polyaniline (PANI)-chemically coated the electrode of quartz-crystal microbalance (QCM) has been developed for the determination of phosphoric acid (H(3)PO(4)) in the liquid phase. The sensing mechanism is based oil the fact that the QCM devices produce a change in the oscillating frequency when the PANI coating the electrode of QCM interacts with different concentration of the acid. This was made during the subsequent redoping-dedoping processes of the PANI film in acid and ammonia solutions, respectively. Also, this was made during the Successive redoping in different acid solutions. The QCM sensor demonstrated a rapid response to the acid with an excellent reversibility. A linear response of the sensor for different concentrations of H(3)PO(4) Was found in region of <= 1 M. The conductivity at different concentration of the acid was also determined. Finally, pH dependence oil the electronic absorption of PANI phosphate film was Studied which indicates that the film can be used as a sensor over a wider pH range of 3-12. This is in comparison to a PANI-sulphate film which shows limited pH absorption dependence (5-8). (C) 2009 Elsevier B.V. All rights reserved.