During experiments, the OA cell was filled with the test solution. A 5-mm thick deionized-water layer filling another cylinder of the same thickness and diameter was used as an immersion between the cell and a home-made ultra wide-band piezoelectric detector. The design of the cell provides a very easy and rapid procedure of solution filling. This procedure consists of the set up of the whole cell except the cover quartz plate. Next, the volume of the test solution corresponding to the inner volume of the cell cylinder is added, and the upper quartz plate is put to the cylinder edge and is moved by slipping it in the horizontal plane, this tightly covering the cell and removing the excess sample liquid. The process of filling and covering the cell takes about 2 s, which is very suitable not only for batch measurements (building calibration curves of stable solutions), but for monitoring kinetic measurements in this study.