RADIOMETER ABL800 FLEX, Reference Manual

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ABL800 FLEX Reference Manual 3. Optical measuring principles
Optical system,
Continued
Construction
(continued) The method used in the analyzer's optical system is visible absorption
spectroscopy.
Step Description
1 The blood sample is transported to the cuvette positioned in the
hemolyzer unit. The temperature of the cuvette is regulated to 37
o
C.
2
1
µ
L of the sample is ultrasonically hemolyzed in the cuvette at a
frequency of about 30 kHz in order to rupture the walls of the red
blood cells so that their content is mixed with the blood plasma,
giving an optically clear solution. There is no bilirubin in the red
blood cells, so after hemolyzation the red blood cell intracellular fluid
dilutes the plasma bilirubin. The calculation discussed in
Measurement and Corrections corrects for this dilution.
To eliminate air bubbles in the sample and to enhance hemolyzation, an
over-pressure of one atmosphere is maintained throughout hemolyzation
and measurement.
3 Light from a 4 Watt halogen lamp is sent to the cuvette via an infra-
red filter and a biconvex lens.
The voltage across the halogen lamp is regulated by a thermostatted
photodiode so that the amount of light sent to the cuvette has a constant
intensity.
4 The light transmitted through the cuvette is guided to the spectrometer via
an optical fiber.
5 The light passes through a slit that directs it towards a combined
mirror and concave grating.
6 The grating separates the light into 128 single wavelengths and the
mirror focuses the 128 light signals on a photodiode array.
7 The photodiode array has 128 diodes or pixels, one for each
wavelength, which convert the monochromatic light signals to
currents.
8 The currents and therefore the intensity of the light signals are
measured at each of the 128 diodes, which form the basis for the
absorption spectrum for a particular sample.
9 The spectrum is sent to the analyzer’s computer, where the
calculations of the oximetry parameter values are made.
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