Shatunov Vladislav M. RussiaFBUZ "Center for Hygiene and Epidemiology in the Kirov Region", st. Svobody, 64A, Kirov, Kirov region, 610000vladislav.shat@yandex.ru Author's articles Improvement of Potentiometric Determination of Ammonium Ions in Surface Waters for the Samples with a High Concentration The prospect of using Shewhart control charts in assessing the quality of ionometric measurements by the method of adding a sample to a standar