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TurbiDirect_6 02/2019
Preparing and using standards – infrequent use
Note:
These instructions apply to all standards except the < 0.1 NTU standard. If you are
using the < 0.1 NTU standard follow the instructions given above.These instructions apply to
standards that have been sitting undisturbed for more than one week or to new standards.
1. Shake the standard vigorously for 2-3 minutes.
2. Let the vial stand undisturbed for 5 minutes.
3. Invert the vial between 5-10 times.
4. Immediately place the vial in the sample chamber and wait for 1 minute (countdown).
Preparing and using standards – frequent use
Note:
These instructions apply to all standards except the < 0.1 NTU standard. If you are
using the < 0.1 NTU standard follow the instructions given above.These instructions apply to
frequently used standards (daily or weekly usage).
1. Invert the vial 10 times.
2. Immediately place the vial in the sample chamber and wait for 1 minute (countdown).
2.3.7 Formazin standards – preparation and handling
2.3.7.1 Preparation of dilution water
Obtain at least 1000 ml of high quality water (e.g. distilled, demineralised or deionised water).
Check the turbidity of the dilution water before use. If the turbidity is greater than 0.5 NTU
(FNU) the water should be filtered with membrane filter (0.1 µm). Clean the required glassware
with 1:1 hydrochloric acid and rinse several times with the dilution water.
2.3.7.2 Preparation of 4000 NTU Formazin Stock Solution
In lieu of preparations we recommend using a 4000 NTU Stock Solution that is available
from specialised suppliers because these standards are high quality and you do not have to
handle the raw materials.
Caution: Please observe the handling instructions of the MSDS. Gloves, goggles and
breathing equipment must be worn!
To prepare a Formazin Stock Solution from raw materials:
1. Dissolve 0.5 g Hydrazine sulfate (NH
2
)
2
H
2
SO
4
in 40 ml dilution water.
2. Dissolve 5.0 g Hexamethylentetramine in 40 ml dilution water.
3. Transfer both solutions quantitativ to a 100 mL volumetric flask and fill to the mark with
dilution water.
4. Mix the solution thoroughly.
5. Allow this solution to stand for at least 24 hours at 25 ± 3°C (77 ± 5°F) in a dark place
(brown glass bottle).
6. The turbidity is developed over this period.
The Formazin Stock Solution has a maximum shelf life of 1 year if stored correctly (in a dark
place). Production of a Formazin Stock Solution is described in "EN ISO 7027" and "Standard
Methods for Examination of Water and Wastewater".
