Abstract A polarographic sensor comprising a pair of electrodes joined by an electrolyte with a multi-layer gas permeable-essentially ion impermeable membrane separating the electrodes and electrolyte from the sample medium. The layers of the membrane are held together so as to prevent migration of electrolyte therebetween to the region overlying the sensing electrode and to prevent the trapping of gas or liquid between the layers in such region. The outer layer of the membrane is preferably formed of silicone rubber while the next layer is formed of a material which is less permeable to gas and water vapor than the outer membrane, for example Teflon. A polarographic sensor employing such a membrane exhibits good time response and minimal flow sensitivity.
A sensor as set forth in claim 1 wherein: said inner layer is selected from the group consisting of polyethylene, polypropylene and a polymer of a fluorinated alkane.
Claim 2
Dependent Claim
19 words
A sensor as set forth in claim 1 wherein: said inner layer is either polytetrafluoroethylene or fluorinated ethylene propylene.
Claim 3
Dependent Claim
29 words
A sensor as set forth in claim 1 wherein: the thickness of said outer layer is less than the product of the thickness of said inner layer and 20.
Claim 4
Dependent Claim
21 words
A sensor as set forth in claim 4 wherein: the thickness of said inner layer is less than about 2 mils.
Claim 5
Dependent Claim
36 words
A sensor as set forth in claim 3 wherein: the thickness of said inner layer is between about 0.5 and 1 mils; and the thickness of said outer layer is between about 3 and 6 mils.
Claim 6
Dependent Claim
34 words
A sensor as set forth in claim 1 wherein: said sensing electrode is composed of a plurality of spaced wires imbedded in an insulating element and exposed at one end adjacent to said membrane.
Claim 7
Dependent Claim
29 words
A sensor as set forth in claim 1 wherein: said holding means comprises means bonding said layers together at their mating surfaces to provide a composite multilayer membrane sandwich.
Claim 8
Dependent Claim
103 words
A sensor as set forth in claim 1 wherein: said inner and outer layers are separate sheets; said sensor including a body having a cavity therein receiving said electrodes and adapted to hold said electrolyte; said inner layer being positioned to close said cavity; said holding means clamping said outer layer under tension over said inner layer to hold inner layer against said body in sealing engagement therewith; and the outer periphery of said inner layer being disposed inside said holding means so that air may escape from between said layers when said layers are mounted onto said body by said holding means.