Ion selective electrodes

DETAILED DESCRIPTION The invention is applicable to ion selective electrodes other than potassium electrodes, and it is applicable to sensors in a wide range of physical sizes and shapes.
However, the invention solves what has been a difficult and limiting problem in that it makes possible in vivo sensing of potassium using the best potassium selective materials that are currently available.
In vivo sensing of potassium is the best known mode for practicing the invention and that mode has been selected for detailed description here.
The best potassium ion selective membrane currently available appears to be the membrane described by D.
M.
Bank, J.
Kratochvil and T.
Treasure in the Journal of Physics, volume 265, published in 1977 at pages 5 and 6.
The membrane is formed by dissolving the following list of ingredients in 3 ml of tetrahydrofuran and then evaporating the solvent material.
Valinomycin--0.
00015 grams Bis-2-ethylhexyladipate--0.
15 grams Nitrobenzene--0.
05 grams Potassium tetraphenylborate--0.
000025 grams High molecular weight PVC--0.
075 grams The product of that process is a PVC membrane essentially hydrophobic, whose hardness or flexibility is a function of the density and quantity of the constituent PVC and the plasticizer.
For convenience, the material is sometimes referred to herein as PVC or potassium selective PVC.
Conventionally, this PVC material is formed into a thin membrane, cut discs of which are glued to the end of a PVC tube.
The interior of the tube is filled with an electrolyte.
The electrolyte is usually a solution containing KCl.
A half cell is immersed in the electrolyte.
The half cell may be formed by dipping a silver wire in molten silver chloride.
An electrode thus described is shown in FIG.
1 of the drawing.
The ion selective PVC membrane 10 is secured to the end of tube 12 by a polymer adhesive shown as a thin annulus 14 at the end of the PVC tube.
A plug 16 inside the tube at a point removed from the membrane serves to retain the body 18 of electrolyte in contact with the membrane 10