A pyrocatechol violet mdoified electrode has been fabricated by dip- coating a pyrolytic graphite electrode in a NH~3.H~2O-NH~4Cl buffer solution of PCV (pH8.5). It has good electroactivity. The anodic peak potential of differential-pulse voltammogram is E~p~a=+80mV. While adding Al, the peak current decreases and the peak potential remains the same. The decreasing value of peak current Δi~p is linear with the Al concentration in the range of 1× 10^-^8-1×10^-^7mol.dm^-^3 and 1×10^-^7-1× 10^-^6mol.dm^-^3. The detection limit is 5×10^- ^9mol.dm^-^3 and the relative standard deviation for 4×10^-^8mol.dm^- ^3 Al is 5.0% (n=8). It was applied to the determination of Al in drinking water samples to give good results. A mechanism of indirect determination of Al by PCV-CME is proposed: (1)the PCV is absorbed on the electrode surface as a monolayer. (2)Al forms an electroinactive complex with PCV absorbed on the modified electrode surface; it covers the electroactive points of the PCV monolayer, which results in the decrease in the peak current. In the absence and presence of Al, the electrochemical current responses of the electrode are always corresponding to the redox reaction of PCV. We utilized the electrochemistry, scanning electron micrograph, X-ray fluorescence spectroscopy and X-ray photoelectron spectroscopy to demonstrate this mechanism.

Key words: CATECHUL VIOLET, ELECTRODE, ELECTROCHEMICAL ANALYSIS, VOLTAMMETRY, ALUMINIUM