The search for a suitable miniature electrode system for in situ measurements of the pH of wet deposition has led to tests with hydrogen-ion sensitive field effect transistors (pH-ISFETs).
Initial testing was done under laboratory conditions and focussed on the stability and reproducibility of the electrode response under flow conditions, firstly with buffered solutions in the pH range 4.1 to 5.0, a range typical for rainfall in this area of Switzerland, and thereafter with unbuffered solutions in the pH range 3.0 to 5.0. Emphasis was also placed on the choice of reference electrode and on the design of the flow cell for field tests. The effect of temperature on the ISFET response - with a view to eventually compensating for this parameter - could be followed by means of a diode mounted on the ISFET holder.
Based on the results of laboratory tests, operational conditions in the field were chosen. Some of the initial field results are presented, and the specific problems occurring with the field model are outlined and discussed.