For the title naproxen-based
ILs, the concentrations of standard solutions were prepared in turn
with double-distilled water as the solvent (4 × 10–4, 8 × 10–4, 1.6 × 10–3, 2.4 × 10–3, 3.2 × 10–3, 4.0 × 10–3, and 1 × 10–2 mol·L–1) and with ethanol as the solvent
(1.0 × 10–2, 1.0 × 10–3, and 1.0 × 10–4 mol·L–1).
First, the pure solvent (50 mL, double-distilled water or
ethanol) was placed in a beaker. During different determination phases,
the standard solution with different concentrations was chosen. After
each addition of standard solution (1.00 mL), the solution was stirred
to ensure homogeneous mixing, and the electrical conductivities and
concentrations of the beaker were recorded with a DDS-307 electrical
conductivity meter (DJS-1C platinum black electrode) at 25 °C.
The DDS-307 electrical conductivity meter operated at an alternating
current of 50 ± 0.5 Hz. The conductivity value of the naproxen-based
ILs was determined after subtracting the electrical conductivity of
solvents (water, 2.02 μS·cm–1; ethanol,
0.35 μS·cm–1) from the measured values.