Thermo Scientific Orion AQUAfast AQ3010 Turbidity Meter User Guide
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Appendix 2
Guide to Good
Measurement Technique
Turbidity is a very complex analytical measurement that can be affected
by many factors . Some are inherent in the instrument’s design such as
angle of detection, light beam aperture, incident beam wavelength and
color sensitivity of the photocell .
However, there are other factors such as stray light, air bubbles and care
of vial, which can be prevented through proper care of equipment and
accessories, and in the operating procedure for measurement . Here are
some points you may want to note .
Sample vials must be meticulously clean and free from significant
scratches . It should be treated on the outside with a thin coat of
silicone oil . This is to mask minor imperfections and scratches that may
contribute to stray light . Sample vials should be handled only by the
top to avoid dirt accumulation (or deposits) and fingerprints that might
interfere with the light path .
More information can be found in the
Vials – Handling, Cleaning and
Care
section .
Best precision and repeatability of turbidity measurement are achieved
using a single, indexed vial . However, for more convenience, different
vials can be used for measurement provided their readings with the same
solution are matched . That is, the meter gives identical readings or within
the specified repeatability and precision of the meter .
Select a few vials . After the sample vials are cleaned, fill them with ultra-
low turbidity water . Allow the sample vials to stand and for air bubbles to
rise . Polish sample vials with silicone oil and take turbidity measurement
at several points while rotating it in the sample well . Find the position
where turbidity reading is the lowest and index it for each vial . Whenever
these sample vials are used, use the indexed mark to position each vial
into the sample well . Choose those vials that match the readings .
Note:
Not all vials can be matched due to some manufacturing variations .
Maintain
Sample Vials
in Good
Condition
Match
Sample Vials
