Page 179 - Analytical Electrochemistry 2d Ed - Jospeh Wang

164 POTENTIOMETRY

FIGURE 5-19 (a) Placement of the two pH and two potassium sensors (0.5 mm diameter)
in the porcine heart. (b) Recorded fall in the pH and increased potassium activity LAD ˆ left
anterior descending coronory artery. (Reproduced with permission from reference 57.)

Miniaturized catheter-type ISE sensors, such as the implantable probe shown in
Figure 5-20 represent the preferred approach for routine clinical in-vivo monitoring
of blood electrolytes. For these intravascular measurements the reference electrode
is placed outside the artery (in the external arm of the catheter), thus obviat-
ing biocompatability and drift problems associated with its direct contact with the
blood.