Hach Lange 2100AN, Instrument Manual

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85
SECTION 10 APPLICATION SPECIFIC
MEASUREMENTS
10.1 Application Specific Methods
Application Specific Calibration (ASC) measurement modes provide the
capability to make nephelometric measurement with direct readout of units other
than NTU. The unit of measurement, initially referred to as -1- and -2-, can be
specified (edited) by choosing alpha numeric characters during method entry.
ASC methods are developed by measuring specific known standards in the NTU
mode. Then, data pairs (NTU vs. Know Standard) are keyed into the instrument
memory (refer to Section 10.2.1). After entry, the instrument displays direct
reading measurements in the custom unit of measure. For custom method
development, consider the following information:
•
Cell adapters are available to accommodate 12- and 13-, 16- or 19-mm
glassware in place of the standard 25-mm sample cells.
•
Optional interference filter modules can be used to select the wavelength of
light used for measurement (see Section 9.1.2 on page 80).
The 2100AN Laboratory Turbidimeter can be used for application specific
measurements when predefined units or standard sample cells are not appropriate.
Two user-defined units of measure (ASC -1- and -2-) let the user define the unit of
measure. For example, an application for monitoring oil in water can be assigned a
unit of OIW, and up to eight calibration points can be stored for the application
specific calibration.
Development of application specific measurements requires a thorough
understanding of the sample being measured. As a general rule, use the following
minimum, sample criteria for successful development of custom applications.
•
Use a homogeneous sample.
•
Determine the effect of temperature on the sample. Provide a means to control
temperature if measurements vary significantly with temperature.
•
Use a well-defined sample. That is, know all of the variables in the sample
that affect absorbance or scatter light. For example, to measure oil in water,
suspended oil must be the primary variable causing light to scatter or absorb.
If other variables in the sample matrix also affect the scattered light detection,
there is no way to discriminate between changes in concentration of
suspended oil and changes in other sample variables.