740 Portable Suspended Solids
21.4 Calibration
When Formazin solutions are used for calibration/testing of sensors, sufficient solution
is required such that the sensor is completely immersed. When using light scatter
sensors it is important that the sensor is positioned away from the sides and bottom of
the container to prevent the light being reflected.
21.5 Storage Life
The turbidity standard should be stored in the Winchester bottle and kept in a cool dark
place. The bottle should be labelled to identify its content and also the date of
preparation should be recorded. The 4000 FTU standard has a shelf life of one year
after which it should be discarded and a fresh solution should be prepared.
Solutions made by diluting the 4000 FTU standard should also be stored in suitably
labelled amber glass bottles and kept in a cool dark place. Solutions above 400 FTU
have a shelf life of one month after which they should discarded. Solutions below 400
FTU should be prepared from the 4000 FTU standard daily.
Solutions can be used outside of the storage lives specified above but any results
taken must acknowledge this and be accepted as less accurate. When using solutions,
watch for flocculation (the particles in the solution will appear to link together), if this
occurs discard the solution and prepare a fresh standard.
172430IM-Iss07 Issue Date 23/10/2014 Page 43of 46
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