• The electrochemical reaction within the Sensor removes oxygen from the thin layer of water in contact with the membrane, so it is necessary to renew this layer i.e. by moving the Sensor through the water, or by natural water flow, or by means of a suitable stirrer. This flow must be induced without the entrapment of air bubbles.
  • You will notice that as the electrode is positioned deeper in the water that the %dissolved oxygen etc. will change. This is due to pressure in the water column affecting the %oxygen calculation. Therefore make measurements, wherever possible, at the same depth.
  • Do not touch the membrane or allow it to touch the bottom of a container.
  • Try to keep the electrode vertical during use.
  • If the membrane cap is wet, shake gently to remove residual fluid. Do not use a cloth to dry.
  • When an electrode is placed in a solution, allow to stabilise before starting to record measurements.
  • If you put pH, Oxygen and Conductivity Sensors (electrochemical type) in the same solution at the same time you may notice interference.
  • The gas permeable membrane isolates the sensor elements from the solution on test but allows the oxygen to enter. This transport can cause the readings to begin to shift after 4 to 5 hours. If possible, recalibrate every two hours.
  • Although the electrode part of the sensor is waterproof, its plug and the Smart Q Oxygen adaptor are not waterproof.
  • The Oxygen electrode is supplied with 2 membrane caps, 60 ml of electrolyte and a piece of polishing paper. Further membranes are available as part of the oxygen maintenance kit.
  • Treat the membrane carefully as it is fragile. The membrane is PTFE so is very resistant to chemical attack. However it should not be used with wetting agents such as detergents and soaps as they break down surface tension and allow water to pass through the membrane. No grease, oil or organics should come into contact with the membrane. 
  • Hydrogen Sulphide (H2S) - a by-product of anaerobic respiration recognised by its rotten egg smell - can be a problem as H2S can pass as a gas through the membrane and attack the silver anode to form Ag2S (a black precipitate). The electrode will not function with this coating, which can be difficult to remove. See cleaning.
  • The gas permeable membrane may be deformed by pressure if the electrode is immersed to any depth, making the results unreliable. 
  • The oxygen permeability of the membrane is temperature dependent. This variation in permeability is automatically compensated by the temperature compensation thermistor over the 5 to 45°C operating range. The compensation will lag, the temperature compensator is inside the anode.
  • No compensation is provided for the effect of atmospheric pressure. Calibration should therefore be carried out at the pressure at which measurements are to be made.
  • Long-term immersion will see drift in the output; the reactions taking place by the silver anode will start to produce less conductive silver salts (mainly AgCl) on the anode and change the conductivity of the anode – cathode circuit. The silver chloride will be seen as dark patches or dulling on the anode.


Cleaning and maintenance

  • Take care not to over stretch the membrane when assembling the electrode, as it will become thinner and over sensitive. A membrane that has been damaged in this way will have an opaque white appearance and should be replaced.
  • After extensive use, the electrode may become sluggish and erratic due to surface contamination of the gold cathode. If this occurs, polish the tip of the electrode with the fine crocus paper provided i.e. lay the crocus paper on a smooth flat surface, hold the electrode vertically on it and polish gently with a circular motion. Polish only enough to restore to a bright clean surface. 
  • A net result of the anodes reaction with the electrolyte (KCl) can be a build-up of AgCl on the silver anode. If the anode is covered in an AgCl deposit (black/brown stains) the electrode will give unreliable results. This deposit may be removed by:
  • Make up a paste of baking soda (bicarbonate of soda - NaHCO3) with some water, leave the tip in the paste for at least an hour then rub with some of the paste until the tip is clean and shiny. Or
  • Soaking the electrode tip overnight in a neat ammonia solution. 
  • If neither of these methods works use either the crocus paper supplied or jeweller’s rouge to remove the stains. Do not scratch the silver; the surface must remain even, or you will create long-term stability problems. 


Note: Ammonia solution is toxic, corrosive and irritant. Please refer to local safety regulations for handling instructions.