Human Elisys Quattro, User Manual

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System Basics
ELISYS QUATTRO - User Manual HUMAN 2-11
2.7 Principles of Methods
2.7.1 Absorbance Photometry
The measurement principle of absorbance photometry plays the most important role
in clinical chemistry. With this method the intensity of a monochromatic light beam of
a suitable wavelength is compared before and after passing through a sample. The
degree of attenuation of intensity of the light beam provides a measure for the con-
centration of the substance under investigation. The photometer consists of a poly-
chromatic or monochromatic light source. In the case of the
ELISYS QUATTRO , this
is a halogen lamp which emits a spectrum. The desired wavelength is filtered out us-
ing a wavelength selector (i. e. a filter). The light with this wavelength passes through
the sample with the substance to be measured in an optically clear solution. A part
of the light is absorbed in the sample. The intensity of the light coming out of the sam-
ple is measured with a measuring cell (detector). The light striking the detector is
converted into an electrical signal and stored as the measurement signal.
2.7.2 Bichromatic Measurement
In the case of the bichromatic measurement principle measurements are performed
at two wavelength, the measuring and the reference wavelength. The measuring
wavelength is close to the absorbance maximum of the chromogen. The absorbance
is mainly dependent on the amount of chromogenic substance in the sample. The
reference wavelength lies outside the absorbance range of the chromogen and indi-
cates the blank value of the sample. The absorbance value of the reference wave-
length is subtracted from the absorbance value of the measuring wavelength. In this
manner external influences such as scratches on the microtiter plate, dust, turbidity
of the solution, and the drift of the electronic measuring instrument can be compen-
sated.