The mass spectrograph with the vacuum spark positive ion source distinguishes between bulk impurities in the electrodes and contaminants present on their surface. Surface contamination can be detected and identified when it is the equivalent of less than 0.01 monolayer in thickness. Impurities in liquids are studied by exposing an electrode to the liquid, thereby contaminating its surface. Two ways of contaminating an electrode surface are described: (a) electroplating of impurities onto the electrode, and (b) evaporation leaving residue on the electrode. Experiments with doped water demonstrate that impurities at a concentration of 10−9atom fraction can be detected. Only about 10−10g of impurity is needed for detection using the evaporation technique. Some applications are discussed.