An apparatus for generating ionisation in electrically conducting liquid, the apparatus comprising: a chamber configured to be filled with electrically conductive liquid; a first electrode and a second electrode located within the chamber; and an optical radiation receiver; wherein an electrically conductive contact area of the first electrode and an electrically conductive contact area of the second electrode are configured to be in contact with the liquid of the chamber wherein the electrically conductive contact area of the first electrode is configured to be smaller than the electrically conductive contact area of the second electrode; the first electrode and the second electrode are configured to receive electric energy and output the electric energy to the liquid in order to cause substance of the liquid to emit optical radiation at the electrically conductive contact area of the first electrode on the basis of densification of the electric energy due to the smaller electrically conductive contact area of the first electrode; the optical radiation receiver is configured to receive the optical radiation for analysis of the liquid; the electrically conductive contact area of the first electrode is controllable; and wherein the apparatus comprises an adjuster configured to adjust the electrically conductive contact area of the first electrode; characterized in that the apparatus further comprises an area meter configured to measure the electrically conductive contact area of the first electrode, wherein the area meter comprises a camera directed to the electrically conductive contact area of the first electrode and configured to capture images of the electrically conductive contact area of the first electrode; and in that the adjuster is configured to adjust the electrically conductive contact area of the first electrode on the basis of measurement data about electrically conductive contact area of the first electrode. a chamber configured to be filled with electrically conductive liquid; a first electrode and a second electrode located within the chamber; and an optical radiation receiver; wherein an electrically conductive contact area of the first electrode and an electrically conductive contact area of the second electrode are configured to be in contact with the liquid of the chamber wherein the electrically conductive contact area of the first electrode is configured to be smaller than the electrically conductive contact area of the second electrode; the first electrode and the second electrode are configured to receive electric energy and output the electric energy to the liquid in order to cause substance of the liquid to emit optical radiation at the electrically conductive contact area of the first electrode on the basis of densification of the electric energy due to the smaller electrically conductive contact area of the first electrode; the optical radiation receiver is configured to receive the optical radiation for analysis of the liquid; the electrically conductive contact area of the first electrode is controllable; and wherein the apparatus comprises an adjuster configured to adjust the electrically conductive contact area of the first electrode; characterized in that the apparatus further comprises an area meter configured to measure the electrically conductive contact area of the first electrode, wherein the area meter comprises a camera directed to the electrically conductive contact area of the first electrode and configured to capture images of the electrically conductive contact area of the first electrode; and in that the adjuster is configured to adjust the electrically conductive contact area of the first electrode on the basis of measurement data about electrically conductive contact area of the first electrode.