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Difference between revisions of "Oxygen signal"

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Revision as of 09:22, 5 November 2019


high-resolution terminology - matching measurements at high-resolution


Oxygen signal

Description

The oxygen signal of the Oroboros O2k is transmitted from the electrochemical polarographic oxygen sensor (OroboPOS) for each of the two O2k chambers to DatLab. The primary signal is a current [mAmp] which is converted into a voltage [V] (raw signal), and calibrated in SI units for amount of substrance concentration [µmol·L-1 or µM].


Reference: MiPNet06.03 POS-calibration-SOP



MitoPedia methods: Respirometry 


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




Template NextGen-O2k.jpg


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



Stability of the oxygen signal

The stability of the oxygen signal of the O2k is evaluated by the (negative) uncorrected slope over time. After smoothing, the slope of a stable sensor should be less than ± 1 pmol·s-1·mL-1 in a 2-mL O2k chamber.
  • Instability of the oxygen signal
  • There is drift of the oxygen signal over short or long periods of time.
  • The signal at air saturation is abnormally high for a given gain setting.
  • The zero current is high (>2.5%) and may show drift.

Oxygen signal does not respond

  • The oxygen signal remains at or close to zero even at high oxygen levels.
  • The signal at air saturation is abnormally low.
  1. Check the gain setting for the affected oxygen channel. Standard setting: Gain 1.
  2. Apply technical service: O2k-Open Support

Raw signal

The raw signal of the polarographic oxygen sensor (POS) depends on the gain setting. The default is Gain 1 in O2k-Series G and higher (gain 2 in previous O2k-Series). The maximum signal is 10 volt. Above 9.99 V, the amplifier is in the saturation range, the apparent signal will remain constant at this value, and the slope will appear to be zero. The raw signal can be modified by choosing an appropriate gain setting.
The raw signal observed during calibration at air saturation depends on experimental temperature, barometric pressure (lower values are obtained above sea level), and the sensitivity of the individual POS. The raw signal is converted to oxygen concentration [µM or nmol/mL] or partial oxygen pressure [kPa] by calibration of the POS. Each gain requires a separate calibration of the oxygen signal. Therefore, after changing the gain you should not only perform a calibration at air saturation (as always before an experiment), but also a new zero oxygen calibration.
Raw signal at air calibration, R1
The voltage recorded at air saturation and with an open chamber is an important instrumental quality parameter. It is one result of a full oxygen sensor test.
» Oxygen calibration - DatLab
If the recorded value is too high, first of all the zero current should be checked. A high zero current will also give a correspondingly higher voltage at air saturation; e.g., if the zero current corresponds to a voltage of 1 V at Gain 1, the voltage at air saturation will typically be 3 V instead of 2 V.
Depending on whether or not a high zero current is found the problem has to be further located by switching components. Typically the problem will be located either on the POS or on the POS connector.
If the zero current if ok, consider the following potential reasons for changes in R1:
  1. The stirrer speed (rpm) may have been changed, or the stirrer may have been left in the off mode. - Re-set the stirrer speed and re-calibrate.
  2. The gain setting may have been changed. - Compare calibration values at identical gain settings.
  3. The block temperature may have been changed. - Compare calibration values at identical temperatures.
  4. R1 is similar, but the oxygen calibration factor of the medium, FM.
  5. The barometric pressure has changed (e.g., experiments carried out at high altitude).
The problem occurred after application of a new membrane:
  1. Lower R1: The membrane thickness may have changed, possibly by inadvertently using two superimposed membranes.
  2. Lower R1: The membrane may have wrinkles in the area of the cathode.
  3. Lower R1: The sensor cap may have not been applied properly in the centre, now partially blocking the cathode.
  4. Higher R1: The membrane may have been overstretched, or a thinner membrane is used.
The problem occurred after re-assembly of the O2k chamber:
  1. Lower R1: The chamber may have been improperly positioned, with the blue POS holder (on the left or right side of the copper block) screwed too far into the chamber housing. This would allow only partial contact between the stirred medium and the cathode. - Follow the O2k-Start instructions (MiPNet22.11 O2k-FluoRespirometer manual) to insert the chamber properly.
  2. The electrolyte in the POS may have partially dried out. - Apply a new membrane, following POS-Service instructions: MiPNet19.18B POS-service.


O2k-Open Support cases

Anonymous user

Question:

Q1: The Oxygen Concentration couldn't go down while I tried zero oxygen calibration. No matter how much solution I added, the oxygen concentration still remain the same. I reassembled, but it still keeps the same. The data is attached.

No response to dithionite.PNG


Q2: The chamber B's oxygen slope is not stable. This is a new problem I have never seen. Please see the attachment.(2019-04-26)

Signal stability.PNG


Q3. The maximum Oxygen concentration of another Oroboros O2k is only about 140 μM. I don't how to increase the starting point of oxygen concentration.


Answer:

A1: I suspect that the dithionite solution was not correctly prepared or not fresh. Dithionite loses activity quite fast, so you need to make it freshly. Please check this site: http://bioblast.at/index.php/Dithionite

A2: While there is a difference between chambers A and B, the stability of the signal is still within the acceptable range of noise given by the specifications of the instrument, see: Oxygen_sensor_test.

A3: You may simply need to calibrate, please see here: http://wiki.oroboros.at/index.php/O2_calibration_-_DatLab