This part of ISO 6145 specifies a method for the preparation of calibration gas mixtures by using electrochemical generation of a calibration component and introduction into a complementary gas flow. By alteration of the gas flow or the charge passed through the cell electrolyte, it is possible to change the composition of the gas mixture. The relative expanded uncertainty of the calibration gas content, U, obtained by multiplying the relative combined standard uncertainties by a coverage factor, k = 2, is not greater than 5 %. The method described in this part of ISO 6145 is intended to be applied to the preparation of calibration gas mixtures in the volume fraction ranges (0,1 to 250) × 10–6. NOTE 1 Gases that can be produced by electrochemical generation are oxygen (O2), hydrogen (H2), hydrogen cyanide (HCN), hydrogen sulfide (H2S), chlorine (Cl2), bromine (Br2), chlorine dioxide (ClO2), ammonia (NH3), nitric oxide (NO), nitrogen (N2), carbon dioxide (CO2), phosphine (PH3), arsine (AsH3) and ozone (O3). NOTE 2 The merits of the method are that a stable calibration gas mixture can be quickly prepared within minutes. NOTE 3 Gas blending systems based on electrochemical generation and thermal mass flow controllers, with the facility of computerization and automatic control, are commercially available. An example is given in Annex A.