Were the Free ammonia and Monochloramine colorimetric methods changed?
Method 10200 Free ammonia and Monochloramine changes
As of early 2015 the Free Ammonia Chlorinating Solution Reagent (Product # 2877436) and Reagent Set (Product # 2879200) have replaced Free Ammonia Reagent Solution (Product # 2877336) and Reagent Set (Product # 2879700). The new chlorinating reagent provides more consistent results, decreased reaction time and simpler procedure steps. These changes require Hach instruments to apply correction factors, or update software of the instrument to use an updated program. Please see the Product Notice-Monochloramine and Free Ammonia for more detailed information.