Device for determining ionic analyte activity

DETAILED DESCRIPTION OF THE INVENTION Although the invention as described hereinafter is directed to a device for potentiometrically determining ion activity through the use of ion-selective electrodes, such device can also be used for other electrical tests of liquid samples.
It is particularly useful for analysis of ionic activity in biological fluids, such as blood serum and urine.
The device is particularly adapted for processing by automated handling equipment, such as that described, for example, in commonly assigned U.
S.
Pat.
No.
4,296,070 (issued Oct.
20, 1981 to Montalto et al).
Referring to FIGS.
1-3, a device 10 has an electrically insulative frame 12 comprising an electrically insulative base 14 and a spacer 16 for receiving electrodes.
Although of insignificant magnitude to show in the drawings spacer 16 is typically thinner than the electrodes so that the electrodes extend beyond the surface of spacer 16.
Two solid electrodes 18 and 20 are mounted in frame 12 in a spaced-apart (i.
e.
electrically isolated) relationship.
Device 10 also includes cover sheet element 22 which is described in more detail hereinbelow.
Electrode pair 18 and 20 can be either (1) an ion-selective electrode and an external reference electrode, for direct mode of determining potentials, or (2) two ion-selective electrodes, for a differential measurement comparing the ion activity of an unknown test liquid with that of a similar reference liquid of known ion concentration.
Referring to FIG.
2, electrodes 18 and 20 are shown as being identical and, therefore, suitable for the differential mode of measurement which is typically made with an electrometer when a test drop 50 of a test liquid is deposited into liquid access hole 26 and contacts electrode 18, and a reference drop 52 of a reference liquid is deposited into liquid access hole 28 and contacts electrode 20.
In FIG.
2, the thickness of the electrode layers have been greatly exaggerated for clarity.
Both electrodes are formed of layers comprising an ion-selective membrane 58 which is selectively permeable to the ion of choice