Zero calibration

high-resolution terminology - matching measurements at high-resolution

Zero calibration

Description

'Zero calibration is together with air calibration one of the two steps of the OroboPOS calibration. It is performed in the closed chamber after all the oxygen has been removed by the addition of dithionite, see MiPNet06.03 POS-Calibration-SOP. Unlike air calibration it is not necessary to perform a zero calibration each day.

Abbreviation: R0

Reference: MiPNet19.18D_O2k-Calibration

MitoPedia methods: Respirometry 

MitoPedia O2k and high-resolution respirometry: DatLab 

Template:MitoPedia SUIT

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MitoPedia O2k and high-resolution respirometry: O2k-Open Support 

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A zero calibration should be performed

• From time to time as a record of instrumental performance: use the template O2k-Calibration-list.

A zero calibration has to be performed

• When measurements are performed at low oxygen (<10 µM).
• Bracketing zero calibrations are required when measurements are performed near the limit of detection at oxygen concentrations close to 5 nM (0.005 µM).
• When a new or serviced OroboPOS is used for the first time.
• When a new membrane was applied to the sensor.
• When the gain is changed.
• When a new POS connector is used.

Zero current

Each polarographic oxygen sensor has a zero current, i.e. a current [µAmp] that flows even at an oxygen concentration of zero, which is converted into a voltage [V] as the raw signal. This zero oxygen signal is taken into account by the zero calibration and can be expressed as % of the raw signal at air saturation. New OroboPOS have a zero signal below 1% of the signal at air saturation. For accurate calibration, the zero signal must be stable, which may be the case for zeor currents up to c. 5% of the signal at air saturation. The stability of the zero current can be assessed by keeping track of calibration values using the "O2k-Calibration-list.xls" template.

» MiPNet19.18D O2k-Calibration.

A high or unstable zero current is usually caused either by the OroboPOS, by the POS connector or by a bad connection between those two parts. Cleaning and applying contact oil to the gold pin and thread connecting the POS-Head and the POS-Connector frequently solves the problem. Otherwise, the problem has to be localized by switching components.

If the problem is located on the POS head an intensive sensor service, should be applied at least two times. If this does not help the sensor probable has to be replaced.

If the problem is located at the POS connector cleaning the connection as described above should be tried again. If the problem was decreased but not solved by cleaning and applying contact oil, the cleaning process may have to be repeated several times. If cleaning the connector does not help the POS connector may have to be replaced.