Wavelength Selection
Introduction
User Defined Reagents
UniCel DxC Systems Instructions For Use A13914
Page 9-18
October 2005
Wavelength Selection
Introduction
The UniCel DxC 600/800 provides a selection of ten wavelengths ranging throughout
the UV-visible spectral region from which to measure the absorbance of a desired
analyte. These are 340, 380, 410, 470, 520, 560, 600, 650, 670, and 700 nm. In order
to run a user-defined reagent, two wavelengths are required: the primary or analysis
wavelength, and the secondary or reference wavelength.
Primary Wavelength Selection
Knowledge of the spectral curve of the chromophore of interest will facilitate proper
selection of wavelengths. The primary wavelength is selected based on the maximum
absorbance peak obtained using the desired chromophore. The secondary wavelength,
which will vary depending on the properties of the chromophore, is used to
compensate for variations in the light intensity each time the xenon lamp is flashed.
For a detailed description of the principles of flash correction, refer to CHAPTER 2,
Theory of Operation in the UniCel DxC Synchron Clinical Systems Reference
Manual.
Secondary Wavelength Selection
To select the optimal secondary wavelength for a given analyte, the following criteria
are recommended:
• The secondary wavelength should be as close to the primary wavelength as possible
without overlapping the spectral curve of the desired chromophore. The secondary
reference wavelength should be near the base of the analytical absorption curve. If
the wavelength selected resides on the spectral curve, a loss of sensitivity may
result.
• In order to minimize any optical interference due to the presence of another
absorption curve, the selection of the secondary wavelength will depend on the
location of the other curve in relation to the primary wavelength of the desired
chromophore. If the second curve overlaps the primary wavelength, there may be
an interference; however, proper selection of the secondary wavelength can function
as a "bichromatic" measurement effectively minimizing or eliminating absorbance
due to the interfering substance. In this instance, the secondary wavelength should
be on the interfering curve at or near a point where the absorbance is at the same
level as the crossover absorbance on the primary wavelength. If, however, the
second curve does not interfere at the primary wavelength, the secondary
wavelength should not be selected within the area encompassed by that curve.
• The shortest distance between the two selected wavelengths (without overlapping
the spectral curve) optimizes the flash characteristics of the lamp, providing better
precision of the absorbance data. It is strongly recommended that precision and
correlation data be accumulated to verify proper selection of the wavelengths as
well as all of the defined parameters.
