L55 and IL55BV2 Sensor Instruction Manual
12 Appendix 1: Preparation of Formazin Turbidity Standard
12.1 Health & Safety Precautions
The chemicals used when following this procedure are harmful, therefore the correct safety precautions must be
carried out. During handling, avoid inhalation and contact with the eyes or skin. Wash hands thoroughly after use.
Refer to the data sheets for further details of the chemicals used.
12.2 Method of Preparation
The preparation of a Formazin Turbidity Standard should be carried out with great care. Absolute cleanliness should
be observed at all times to avoid any contamination of the solution.
All water used should be freshly distilled or de-mineralised. During preparation and use, keep the solution covered to
prevent contamination.
1. Dissolve the Hydrazinium Sulphate 10g (32112680) into 1 litre of water. Stir the solution thoroughly.
2. Dissolve the Hexamine 100g (32112630) into 1 litre of water. Stir the solution thoroughly.
3. Pour the above solutions into a 2.5 litre Winchester or similar type amber glass bottle and mix thoroughly. Allow the
mixture to stand undisturbed for 24 hours at 25
°
C. The resultant solution will have a turbidity of 4000 FTU.
4. Prior to use the standard should be mixed thoroughly, i.e. before pouring out the standard, shake the bottle well.
12.3 Preparation of Dilution’s.
The 4000 FTU standard can be used to prepare solutions of lower values by diluting with water. The formula below
can be used to calculate the ratio of water to 4000 FTU standard to produce a solution of the required value.
W
A
=
−
4000
1
W = parts water to 1 part 4000 FTU standard
A = Required FTU value
The Formazin Dilution Chart (table QAP 6.14.4) provides the mixture requirements to make various solutions using the
4000 FTU standard.
12.4 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.
12.5 Storage Life
The turbidity standard should be stored in a 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 be
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.
163790IM-Iss05 Issue Date 11/05/210
Page 19 of 22
