Arkray AUTION ELEVEN AE-4022, Operating Manual

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AE-4022
vi
Technology and Scientific Principles
Reflectance spectroscopy is a commonly used means of obtaining the concentration of a particular analyte
in urine analysis. By reading the light reflected, the instrument measures the end product of the chemical
reaction between the urine analyte and the reagent on the pad.
Each of the reagent strip pads reflect a given color and shade when immersed in urine which is indicative
of the analyte concentration. The strip enters the AUTION ELEVEN AE-4022 where it is auto-aligned and
a set of LED’s directs a single wavelength for measurement (635 nm or 565 nm) at each reagent pad on
the test strip. Glucose, protein, pH, specific gravity, and blood determinant pads receive 635 nm and
bilirubin, urobilinogen, ketone, nitrite, and leukocyte pads receive 565 nm. The pad for blood determination
is the exception and does not receive a reference wavelength. The instrument reader detects the
reflectance of the given wavelength off of each individual pad as an indicator of analyte concentration.
To reduce lot-to-lot and device-to-device variability in the instrument and test strips, additional design
features were added. To mitigate variability in the cumulative factors affecting light measured, the infrared
wavelength (760 nm) is also directed at every pad (except blood) to be used as a reference. To mitigate
variability of the color of urine samples (and test strips), there is a reagent-free, additional pad on every strip
also to be used as a reference. Therefore, each analyte has a reflectance off its own pad to compare with
the reflectance of the infrared off its own pad and the reflectance of its wavelength and the infrared
wavelength off of the reference pad. Therefore, where R is reflectance of the particular analyte.
By dividing out the urine color that gave additional reflectance and by multiplying the reciprocal of the infrared
reflectances, variability is mathematically cancelled out and the truest analyte reflectance is determined.
R
analyte pad
R
× R =
reference pad
R
infrared at reference pad
R
infrared at analyte pad