Vereinfachte DEMS-Apparatur - Kontinuierlicher Nachweis flüchtiger Stoffe in Prozeß- und Abwässern

DEMS (Differential Electrochemical Mass Spectrometry) is used world wide for the on-line examination of electrochemical processes with volatile products. Compared with known devices the mass spectrometric apparatus with membrane inlet system was simplified and built with commercially available components. Some advantages of this experimental set up are the ability to simply control the pressure in high vacuum and the safe handling. In the experiments described a new, readily available membrane was used, showing some advantages compared to the usual membrane. The limited evaporation rate of the solution at the membrane into the vacuum was due to nearly saturated vapor layer at the phase boundary liquid/gas. Applying DEMS the apparatus is coupled to an electrochemical cell. With a special thin layer flow cell the continuous detection of volatile substances in liquids is possible. The determination of chlorinated hydrocarbons is linear over a range of four decades with high sensitivity of about 1 myg/1.