Appendix Eturbidity Measurements - YSI 6 series User Manual

Turbidity Measurements Appendix E
APPENDIX E TURBIDITY MEASUREMENTS
This appendix is in the format of "frequently asked questions, is designed to allow users to optimize the
performance and trouble-shooting problems for your YSI 6136 turbidity probe by supplementing the
discussion of turbidity that is provided in the other sections of this manual (Getting Started, Basic
Operation, Principles of Operation, and Maintenance).
Where should I get my turbidity standards?
To properly calibrate YSI turbidity sensors, you MUST use standards that have been prepared according to
details in Standard Methods for the Treatment of Water and Wastewater (Section 2130 B). Acceptable
standards include (a) formazin prepared according to Standard Methods; (b) dilutions of 4000 NTU
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formazin concentrate purchased from Hach; (c) Hach StabCal standards in various NTU denominations;
and (d) AMCO-AEPA standards prepared specifically for the 6136 by either YSI or an approved YSI
vendor as listed on YSI website (www.ysi.com). STANDARDS FROM OTHER VENDORS OTHER
THAN HACH, YSI, OR YSI-APPROVED ARE NOT ACCEPTABLE FOR USE WITH THE YSI
TURBIDITY SYSTEM AND THEIR USE WILL LIKELY RESULT IN BOTH CALIBRATION
ERRORS AND INCORRECT FIELD READINGS.
For the best combination of accuracy and ease of use, we recommend that you use standards that have been
prepared from AMCO-AEPA polymer beads by either YSI or a YSI-approved vendor. This material is
listed as a secondary turbidity standard by Standard Methods for the Examination of Water and Wastewater.
These standards have been certified to be the proper value in NTUs by comparison of their turbidity outputs
with those of freshly prepared formazin, the latter being the most accepted primary standard for turbidity. The
polymer standards can be linearly diluted with turbidity free water to generate standards that are lower in
value and which can then 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
from Hach as a 4000 NTU suspension that can be linearly diluted to form lower NTU standards. In addition,
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Hach offers formazin turbidity standards in a variety of NTU values under the StablCal designation and
these standards may prove useful for the calibration of your YSI turbidity sensor. The advantage of the use of
formazin is its cost; the primary disadvantage is that it is a somewhat 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 may be less stable to degradation in dilute form. If you use formazin, we recommend that
TM
you purchase from Hach either the 4000 NTU concentrate and dilute it or the StablCal standards in the
proper turbidity concentrations for your application, 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, be very safety conscious if you use it and be sure to follow the manufacturer's instructions with
regard to its handling and disposal.
Remember that is imperative that you do NOT use standards that are based on suspended materials other than
formazin or AMCO-AEPA polymer or have been prepared by vendors other than YSI, YSI-approved
suppliers, or Hach. These standards will NOT read correctly when measured with the YSI turbidity systems.
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 and were prepared by the proper method.
Do I have to buy turbidity-free water for the 0 NTU calibration?
For most applications, purified water of any kind (distilled, deionized or 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. It is
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