Turbidity Calibration Standards - novomatics Turbitronic P Operation Manual

Novomatics Manual

13. Turbidity calibration standards

In turbidity measurements, primary turbidity standards are required as these are the only
certified standards. By diluting a primary turbidity standard, a secondary standard can be made
for actual use. The derived turbidity value is traceable to the original primary standard. It is
accepted that dilutions are less stable and cannot be used over a longer period of time (max. 1
week). The definition of turbidity units is based on the polymer suspension FORMAZIN. A
FORMAZIN primary turbidity standard is specified for 1000 Nephelometric Turbidity Units
(NTU). A wide range of secondary standards can be made by dilution with distillated water (see
calibration procedure). A 1000 NTU turbidity standard is stable for long period of time (max. 1
year). Titration of FORMAZIN has proven to be the fastest and most convenient means of an
accurately working turbidity standard.
For recalibration of the turbidity, the special polymer suspension FORMAZIN is recommended
(available from the manufacturer/supplier). FORMAZIN primary standards are supplied in
sealed dark brown 0.1 l bottles and can be used till 1 year after supply date. In order to prepare
a secondary standard, one can dissolve a small portion of the primary standard in distilled water
by using standard glassware. The following table is providing the example ratios to be mixed.
Desired Standard
250 NTU
100 NTU
0 NTU
Table 3 NTU example ratios
Swirl the glass to mix the solution. Then pour the prepared secondary standard into a
Turbitronic P test tube and use the provided plastic covers for easy handling.
1000 NTU primary
standard in
50 ml glass
12.5 ml
5 ml
0 ml
Turbitronic P
Destilled water
in
50 ml glass
37.5 ml
45 ml
50 ml
24