at each level of the NaNO3 concentration, but at each level of the
current intensity, the ECL intensity decreased with the increase of
NaNO3 concentration from 0.2 mol L−1 to 5.0 mol L−1. To obtain the
maximum ECL intensity, a 80mA current and a 0.3 mol L−1 NaNO3
solution were selected for subsequent studies.The ECL emission of
naproxen in neutral and acid NaNO3 solution was very weak, but
strong in basic NaNO3 solution. The alkalinity of the supporting
electrolyte was investigated by adding various concentrations of
NaOH into the supporting electrolyte. The results (Fig. 4) showed
that the ECL intensity increased with the increase of the NaOH
concentration from 0mol L−1 to 0.24mol L−1 and then decreased
with the increase of the NaOH concentration from 0.24mol L−1 to
0.6 mol L−1.
Acetonitrile or methanol was the generally used organic mobile
phase in reversed-phase high-performance liquid chromatography,
and in most cases it has important effect in post-column CL or
ECL detection. The ECL emission of naproxen in the medium of
acetonitrile/water and methanol/water were compared. As shown
in Fig. 5, the ECL intensity in acetonitrile/water was higher than
that in methanol/water. In the medium of acetonitrile/water,
the ECL intensity increased with the increase of the ratio of
acetonitrile/water from 10% to 80%, while in the medium of
methanol/water, the ECL intensity decreased with the increase of
the ratio of methanol/water. Thus, it could be seen that the ECL
reaction of naproxen is well compatible with a mobile phase of
acetonitrile/water.
Fig.