HORIBA’s ENDA-5000 Continuous Emission Monitoring System (CEMS) is used for continuous monitoring of NOX, SO2, CO, CO2and O2 in stack gas, produced by stationary sources like power plants, boilers, gas turbines, furnaces, chemical plants, etc. Prior to the introduction of new CEMS to the European Market, the whole system must be tested and approved by the European certification agency, for example TUV in Germany or MCERT in the U.K. There are lots of test procedures, which are applied to CEMS during the certification process in the laboratory as well as in the field under real process conditions. CEMS units must comply with the conditions that are specified in European standard EN 15267-3.[1]One of the most important items is the test for resistivity of CEMS system against disturbing or interfering chemical components.