LaMotte SMART Spectro Spectrophotometer - Manual (Page 127)

A reagent blank should be run with each set of samples and with each lot of
reagents.
The reacted blank will be stable if stored in the dark.
To eliminate error caused by contamination, wash all glassware with 20% sulfuric
acid.
For greater accuracy, a minimum of three repetitions should be performed and the
results averaged.
Some samples may be digested completely in less than two hours. The
concentration may be measured at 15 minute intervals while the vials are still
hot until the reading remains unchanged. The vials should be cooled to room
temperature before the fi nal measurement is taken.
COD, Standard Range SMART Spectro Test Procedures 2.11
Test P
rocedures