12
Appendix
Appendix
Indexing a sample vial
The United States Environmental Protection Agency (U.S. EPA) recommends that the vial used for turbidity calibration or sample measurement be
indexed. Its purpose is obtain a position which provides the lowest turbidity reading. The indexing methods are as follows.
1.1 Fill the vial using the distilled water (< 0.5 NTU). Cap the vial.
1.2 Wipe the vial with the lint-free cloth to remove waterdrops and fingerprints.
1.3 Place the vial in the measurement chamber. Align the mark on the vial with the arrow on the meter.
1.4 Press the
Meas
key, the meter begins the measurement.
1.5 Slowly rotate the vial approximately 45 degrees. Close the light shield lid and record the measured value.
1.6 Repeat the step 1.5 until the lowest turbidity reading is shown.
1.7 Mark this position on the vial.
Matching the sample vials
For the best accuracy and repeatability, using one indexed vial is best choice for turbidity measurement. If you need to use a few vials, match
these vials are necessary.
2.1 Repeat the steps above for each vial and record the measured values.
2.2 Find the closest position of these vials measuring value and mark it.
Preparing the formazin standards
Preparation of turbidity-free water:
The turbidity-free water is used for preparation of turbidity standards and is prepared by filtering deionized water through a 0.45µ m or smaller
pore-sized membrane.
Preparation of turbidity standards:
Turbidity Standard
Preparation Method
4000 NTU
•
Dissolve 1g hydrazine sulfate [(NH
2
)
2
•
H
2
SO
4
] in the turbidity-free water and dilute to 100ml in a volumetric flask.
•
Dissolve 10g hexamethylenetetramine [(CH
2
)
6
N
4
] in the turbidity-free water and dilute to 100ml in a volumetric
.
flask.
•
Mix 5ml of hydrazine sulfate and 5ml of hexamethylenetetramine solutions in a 100ml volumetric flask and let
.
stand 24 hours at 25
(± 3)° C.
1000 NTU
Mix 25ml of 4000 NTU standard in a 100ml volumetric flask and dilute to the mark.
500 NTU
Mix 12.5ml of 4000 NTU standard in a 100ml volumetric flask and dilute to the mark.
200 NTU
•
Mix 10ml of 4000 NTU standard in a 100ml volumetric flask and dilute to the mark.
•
Mix 50ml of above standard in a 100ml volumetric flask and dilute to the mark.
10 NTU
•
Mix 10ml of 4000 NTU standard in a 100ml volumetric flask and dilute to the mark.
•
Mix 2.5ml of above standard in a 100ml volumetric flask and dilute to the mark.
Or,
mix 2ml of 500
NTU standard in a
100ml volumetric flask and dilute to the mark.
