RADIOMETER FLEX ABL90, Справочное руководство

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5. Sensors and optical system ABL90 FLEX reference manual
5-40
The method used in the analyzer's optical system is visible absorption
spectroscopy. The measurement cycle consists of the following steps:
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 °C.
2 A back pressure is exerted on the sample. This one atmosphere
over-pressurization is maintained throughout the hemolyzation and
measurement to eliminate air bubbles in the sample and to enhance
the hemolyzation process.
3 The one-µL sample in the cuvette is ultrasonically hemolyzed at a
frequency of about 30 kHz. This hemolyzation process ruptures the
walls of the red blood cells, evenly mixing the content of the red
blood cells with the plasma and producing an optically clear
solution.
4 Light from a white LED is emitted to the cuvette and the light
transmitted through the cuvette is guided to the spectrophotometer via
an optical fiber.
5 The light passes through a slit that directs it towards an
arrangement of mirrors and a grating.
6 The grating separates the light into the colors of the rainbow and
the mirror focuses the light on a photodiode array.
7 The photodiode array has 256 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 256 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.
The 256 channels are standardized into 138 selected wavelengths.
Absorption spectroscopy is based on Lambert-Beer's law, which states that the
measured absorbance for a single compound is directly proportional to the
concentration of the compound and the length of the light path through the
sample
[
2
]
:
y y y
A c l
 

  
where:
y
A

= absorbance of compound y at wavelength

y


= extinction coefficient of compound y at wavelength  (a constant,
characteristic of the compound)
y
c
= concentration of compound y in sample
l = length of the light path
Measurement
cycle
Lambert-Beer's
law