(OS 418 : Clark-type O2)

Electrode Design

The OS-418 oxygen sensor is a miniature, Clark-type amperometric sensor that is designed for measuring static as well as dynamically changing oxygen levels in aqueous and physiologic fluids. The oxygen sensor consists of a pair of miniaturized electrodes immersed in a drop of aqueous  KCl electrolyte and separated from the test environment by a replaceable oxygen permeable membrane. An outer Ag/AgCl anode surrounds an internal platinized platinum cathode. The 5 mil (0.005") diameter high purity platinum wire cathode is fused into a glass sheathing that fills the lumen of the outer silver body. The oxygen permeable membrane is placed over the tip of the electrode assembly and secured with an O-ring. With the membrane and O-ring in place, the sensor diameter is 4.5 mm (0.177"). The sensor may be housed in an black delrin body that exposes only the membrane-covered tip of the sensor to your test solution.

General Specifications:

Sensor Probe Length 4.182 cm
Sensor Housing Length 2.5 cm
Sensor Diameter 0.318 cm
Sensor Housing Diameter 0.787 cm
Connector Type Modified Amphenol Sub-Minax P/N 27.9

Technical Specifications:

Sensor Sensitivity 0 - 150 mm Hg
Response Current for Ambient pO2 18 nA
Time Constant / Response Rate (0 - 63%) 4 s
Bias Voltage Required -0.7 V
Thermal Drift 4 % / C

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Applications in Research and Development
  • As an oxygen-level sensor in Micro-BOD (Biological Oxygen Demand) measurements.
  • In monitoring oxygen levels in cell cultures.


Principle of Operation

Using a constant voltage source (potentiostat, OSI-1 or OSI-2), a constant -0.7 V bias voltage is applied between both electrodes [cathode (-) and anode (+)] of the sensor. In the absence of any other oxidizable species (and there should not be any in aq. KCl), this results in a current that is directly proportional to the RATE at which molecular oxygen is electrolytically discharged at the cathode. The steady state discharge rate is dependent upon diffusion of oxygen across the polymer membrane that covers the two electrodes. If all the oxygen that arrives at the cathode is summarily discharged, then the discharge rate (current) is directly proportional to the flux (amount per unit area per unit time) of oxygen across the membrane. This flux is directly proportional to the extra-membrane concentration of dissolved oxygen. In this way the observed current is made indirectly proportional to the oxygen concentration.

The OS 418 Oxygen Sensor Package Contains:

1 Oxygen Sensor
5 reusable O-rings
1 Sheet of 0.001; Polyethylene Membrane
1 Membrane Installation Tool (white, cone-shaped) 1 Sensor Housing (two parts) (black delrin)
1 Oxygen Sensor Operations Manual

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  • Requires Sensor Cable Model SC9BNC (sold separately): Model SC9BNC is a flexible coaxial cable with a female Sub-Minax connector on one end (to the OS-418 oxygen sensor) and a BNC connector on the other to the OSI-2 instrument.
  • Requires Oxygen Sensor Instrument Model OSI-1 (single channel) or Model OSI-2 (dual channel) (sold separately). Model OSI-1 is a single channel oxygen sensor interrogation system for use with the Model OS-418 oxygen sensor.
  • For best results, the OS-418 requires thermal regulation of the test solution and electrode to avoid appreciable thermal drift.

Last Revision 08/12/01; (c) 2000-2001 ABTECH Scientific, Inc.

Contact: Ann M. Wilson, Manager,
Applications Development ABTECH Scientific, Inc.
911 East Leigh Street G24, Richmond, Virginia 23219
Telephone Number: +1-804-783-7829 Fax Number: +1-804-783-7830

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