Developing Applications Using Alternate Wavelengths; Measurements In Color, % Transmittance And Absorbance; Using Color Units (Platinum Cobalt Color Units Calibration Procedure) - Hach 2100AN Instrument Manual

SECTION 9,
continued

9.1.2 Developing Applications Using Alternate Wavelengths

9.2 Measurements in Color, % Transmittance and Absorbance

9.2.1 Using Color Units (Platinum Cobalt Color Units Calibration Procedure)

It may not be possible to complete measurements in all units of measure for a
particular application using the optional filter assemblies (especially
nephelometric modes that include NTU, EBC, Neph and ASC units). For
example, the NTU unit of measure may not be suitable at a 560-nm wavelength
for a particular sample, but the measurement could be completed in Absorbance
(A) or Transmittance (%T) modes.
Insufficient light is the problem that may be encountered most often when using
the NTU, EBC, Neph and ASC units of measure with the optional filters. The
2100AN provides a low-light warning indicated by a flashing lamp annunciator.
This limitation can be overcome using the cell adapters and smaller sample cells
to provide a shorter light path.
To develop applications using the optional filter assemblies:
1. Prepare a series of standards solutions that span the range of interest.
2. Select the filter assembly providing the desired wavelength, and install it in
the instrument.
3. Select the desired unit of measure.
4. Measure the standards, and plot the response.
5. Repeat the test using one of the optional cell adapters and a smaller sample
cell if a low-light indication occurs.
Many low-light conditions encountered in developing applications at alternate
wavelengths can be resolved with the proper selection of the measurement unit,
wavelength and cell-path length.
The 2100AN provides for measurement and direct measurement of scattered,
percent transmitted (%T) or absorbed (Abs) light. Therefore, turbidity, color
(Pt-Co units), %T and Abs can all be determined on a single sample.
Hach Company recommends using the Flow Cell in these measurement modes for
best results.
Color methods using a wavelength other than 455 nm can be developed using
selected interference filter assemblies.
Note: The 15 CU Pt-Co standard is recommended when measuring low-color
concentrations. Use the 500 Pt-Co CU standard if concentrations are expected to be
greater than 30 CU.
Note: Prepare a 15 CU standard by diluting 15 mL of the 500 CU standard (Cat. No.
1414-53) to 500 mL with deionized water in a volumetric flask.
Note: Use of a Flow-Cell Kit is recommended. A Flow-Cell Kit is required to achieve cited
instrument accuracy and reproducibility specifications. Use of a Flow Cell is especially
important when measuring low level color.
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