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Closure

The closure creates an airght seal necessary for proper uid movement within the cartridge. The

closure also ensures that calibrant and sample remain contained within the cartridge during the tesng

cycle and subsequent disposal.

Cartridge on the le in the illustraon contains natural rubber latex on the snap closure. The cartridge

shown on the right is not made with natural rubber latex.

Heang elements

All i‑STAT cartridges require thermal control at 37°C (98.6°F), and include heang elements on the

underside of the sensor chips which are contacted and heated by the instrument's thermal probes.

Standardizaon and calibraon

Standardizaon is the process by which a manufacturer establishes “true” values for representave

samples. A mul-point calibraon curve, the slope or sensivity of which is dened by coecients in the

CLEW soware, is derived for each sensor by this standardizaon process. These calibraon curves are

stable over many lots.

A one-point calibraon is performed each me a cartridge requiring calibraon is used. During the rst

part of the tesng cycle, the calibrant soluon is automacally released from its foil pack and is

posioned over the sensors. The signals produced by the sensors’ responses to the calibrant soluon are

measured. This one-point calibraon adjusts the oset of the stored calibraon curve. Next, the

instrument automacally moves the sample over the sensors and the signals produced by the sensors’

responses to the sample are measured. While coecients are used rather than graphic calibraon

curves, the calculaon of the result is equivalent to reading the sample’s concentraon from an adjusted

calibraon curve.

Types of cartridge sensors

Sensors are thin lm electrodes microfabricated onto silicon chips. Sensing funconality is imparted to

each electrode by a number of chemically sensive lms coated over the acve region of the electrodes.

The cartridges have three dierent types of sensors built in: potenometric, amperometric, and

conductometric.

Potenometric sensors

In potenometric measurements, the dierence in potenal that exists between an indicator

electrode and a reference electrode is measured. Ion-selecve electrodes (ISE) are examples of

potenometric sensors. The indicator electrode is designed to be sensive to a parcular ion in a

soluon. In cases where other ions are sensed by the system, selecvity coecients can be used

to correct for this interference. An enzyme can be added to an ISE to produce ions from analytes

of interest that are not themselves ions.

Potenometric sensors ulize two important concepts. The rst concept is the Nernst Equaon

which relates the measured potenal to the acvity of the ion being measured. It is wrien as:

E = E° + RT/nF ln a

i-STAT Alinity — System Operaons Manual Art: 745524-01 Rev. I Rev. Date: 02-Nov-2022

Abbott i-STAT Alinity User Manual

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