RADIOMETER FLEX ABL90 User Manual

29
General measuring principles
Introduction
There are four different measuring principles employed in the sensors in the ABL90 FLEX analyzer.
• Potentiometry: The potential of a sensor chain is recorded using a voltmeter, and related to the
concentration of the sample (the Nernst equation). The potentiometric measuring principle is
applied in the pH, pCO
2
, K
+
, Na
+
, Ca
2+
and Cl
–
sensors.
• Amperometry: The magnitude of an electrical current flowing through a sensor chain is
proportional to the concentration of the substance being oxidized or reduced at an electrode in
the chain. The amperometric measuring principle is applied in the cGlu and cLac sensors.
• Optical pO
2
: The optical system for pO
2
is based on the ability of O
2
to reduce the intensity and
time constant of the phosphorescence from a phosphorescent dye that is in contact with the
sample. This measuring principle is applied in the pO
2
sensor.
• Spectrophotometry: Light passes through a cuvette containing a hemolyzed blood sample.
The specific wavelengths absorbed and their intensity generate an absorption spectrum used
to calculate oximetry parameters. This measuring principle is used for measuring ctHb, sO
2
,
FO
2
Hb, FCOHb, FHHb, FMetHb, FHbF and ctBil.
Activity vs. concentration
Strictly speaking, in potentiometry the potential of a sensor chain is related to the activity of a
substance, and not its concentration.
The activity of a substance can be considered the "effective concentration" of a species, taking
non-ideality of the medium into account.
Activity and concentration are related by the following equation:
a
x = γ cx
where:
a
x = the activity of the species x
γ = the activity coefficient of species x under the measurement conditions (for ideal systems γ = 1)
c
x = the concentration of species x (mol/L)
Note: To be exact, activity is related to the molality of species x, i.e. the number of mol/kg of
solvent. However, molality is converted to concentration (molarity).
Theoretical aspects of the blood gas analyzer
29 of 36EXT-VEND-MAN-0023-1 Owner:Julie Monnox Approved:27 Mar 2019

RADIOMETER FLEX ABL90 Specifications

General

Analyzer Type	Blood Gas Analyzer
Analysis Time	35 seconds
User Interface	Touch screen
Power Supply	100-240 V AC, 50/60 Hz
Parameters Measured	pH, pCO2, pO2
Sample Type	Whole blood
Sample Volume	65 µL
Calibration	Automatic
Connectivity	USB, Ethernet
Operating Temperature	15-30°C
Operating Humidity	20-85% relative humidity, non-condensing