How do the wavelengths vary for each of the COD reagents?
COD calibration curves
The COD calibration curves for Hach procedures vary. The High Range+ (Product # 24158-xx), High Range (Product # 24259xx) and the Ultra-low (Product # 24158xx) COD calibrations are curves with a positive slope when zeroed on a deionized (DI) water reagent blank. The low range (Product # 24258xx) COD calibration is a curve with a negative slope when zeroed on DI water reagent blank.