YSI 6000UPG - Manual (Page 166)

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significant benefit and more than likely will be necessary for most deployments. Even if fouling
from chemical or biological sources is not a significant problem in your unattended application,
it is likely that bubbles will form on the optical surface during deployment and result in the
transmission of erroneous readings. Further, once bubbles have formed, they can remain in
place for long periods of time, resulting in corrupted readings for the majority of the study. YSI
feels that mechanical cleaning is a necessity for unattended monitoring of turbidity.
Question 2: Where should I get my turbidity standards?
Naturally, we recommend that you obtain your standards from YSI. We sell 100 NTU standard
which is has been prepared from the AMCO-AEPA polymer which is suggested for use as a
secondary turbidity standard by Standard Methods for the Examination of Water and Wastewater.
This YSI standard has been certified to be 100 NTU by comparison of its turbidity output with that
of freshly-prepared formazin, the latter being the most-accepted primary standard for turbidity. The
YSI polymer standard can be linearly diluted with turbidity free water to generate standards which
are lower than 100 NTU and can also be used as calibrants. For example, diluting 50 mL of 100
NTU standard to a total volume of 500 mL will yield a 10 NTU standard.
You can also use formazin as your source for turbidity standards. The formazin can be generated
by the procedure found in Standard Methods for the Examination of Water and Wastewater, or it
can be purchased as a 4000 NTU suspension which can be linearly diluted to form lower NTU
standards. The advantage of the use of formazin is its cost; the primary disadvantage is that it is a
hazardous reagent for which care must be taken in handling and disposal. In addition, formazin
settles out much more rapidly than the AMCO-AEPA polymer and is less stable to degradation in
dilute form. If you use formazin, we recommend that you purchase the 4000 NTU concentrate and
dilute it, rather than generating the reagent from the chemical reaction described in Standard
Methods for the Examination of Water and Wastewater. Whatever your source of formazin,
however, be very safety conscious if you use it and be sure to follow the manufacturer’s instructions
with regard to its handling and disposal.
Finally, it is important that you do not use standards which are based on suspended materials other
than formazin or AMCO-AEPA polymer. These standards may not read correctly when measured
with the near infrared light source (860 nm) of the 6000
UPG probes. If you have any doubts about
the composition of your standards, consult your supplier and be certain that they are based on either
formazin or AMCO-AEPA materials.
Question 3: Do I have to buy turbidity free water for the 0 NTU calibration?
For most applications, purified water of any kind (distilled, deionized, filtered) will be acceptable
for the 0 NTU standard. This water can be obtained from a laboratory or can be purchased at a
local supermarket. However, we do not recommend that you use tap water as the 0 NTU standard.
For maximum accuracy at very low NTU values (below the specification of the instrument), you
may want to purchase turbidity-free water from YSI or another vendor. However, these occasions
are rare. Just be sure to use purified water that is visually free of any suspended material.