Page 176 - Analytical Electrochemistry 2d Ed - Jospeh Wang

5-3 ON-LINE AND IN-VIVO POTENTIOMETRIC MEASUREMENTS 161

FIGURE 5-16 Coated-wire ion-selective electrode. (Reproduced with permission from
reference 41.)

reproducibility. The principles and applications of CWEs have been reviewed (4).
The possibility of eliminating the internal ®lling solution is receiving considerable
interest in connection with mass production of potentiometric sensors and sensor
arrays (see Section 6-3.2).

5-3 ON-LINE AND IN-VIVO POTENTIOMETRIC MEASUREMENTS

Various on-line monitoring systems can bene®t from the inherent speci®city, wide
scope, dynamic behavior, and simplicity of ISEs. In particular, ISEs have become
widely used as detectors in high-speed automated ¯ow analyzers, such as air-
segmented or ¯ow injection systems (45,46). For example, Figure 5-17 shows the
¯ow injection determination of physiologically important potassium in serum, using
a tubular potassium selective electrode, at a rate of 100 samples per hour. Even
higher throughputs, reaching 360 samples per hour, have been employed in
connection with air-segmented ¯ow systems (48). Such analyzers are now being