obvious ECL signal was observed in its corresponding ECL–potential
curves (Fig. 7b, lines 1 and 3). For a solution in the presence of
1.0×10−4gmL−1 naproxen, the oxidation peak of water around
1.5V decreased (Fig. 7a, lines 2 and 4). Companied with the oxidation
of water, weak ECL signal was observed around 1.5V in its
corresponding ECL–potential curves (Fig. 7b, line 4), and stronger
ECL emission was observed when the potential was more positive
than 2.5V (Fig. 7b, line 2). Further experiments showed that
the ECL intensity from the counter electrode was 25 times higher
than that from the working electrode. Namely, the ECL emission
was mainly from the electrode on which the reduction reaction
occurred.
In order to identify the light emitter, fluorescence spectra were
measured. The excitation spectrum of naproxen has two peak
around 263nm and 332 nm(Fig. 8, line 1), and the maximum emission
spectrum was around 352 nm (Fig. 8, line 2). The fluorescence
intensity of naproxen decreased after 10 min electrolysis (Fig. 8,
lines 3 and 4) and no new spectrum was observed. The ECL spectrum
was also recorded. The maximum wavelength was around
438 nm, which was largely different form the fluorescence emission
spectrum of naproxen. The results indicated that naproxen
was consumed in the electro chemical reaction and new unstable
intermediate was produced. Considering that nitrate could be
reduced electrochemically [23,24], it seemed reasonable to suppose
that naproxenwas electrochemically oxidized to produce an unstable
intermediate. This unstable intermediate further reacted at the
counter electrode with the reduction product of nitrate to generate
the ECL emission. However, the detailed mechanism is still unclear
and a deeper investigation of these reactions is needed.
Fig.