Page 365 - Instrumentation Reference Book 3E

348 Chemical analysis: electrochemical techniques
Where measuring cells are installed in pipe-
work, it is essential that they are positioned in a
rising section of the system to ensure that each
cell is always full of electrolyte, and that pockets
of air are not trapped.

Cleaning and muintenunce .f cells Periodic
inspection and cleaning of conductivity cells is
essential to ensure that the electrode surfaces are
Pipeline or container
free from contamination, which would otherwise
alter the electrode area and effective cell constant.
The frequency of such procedures is mainly
dependent on the nature of the samples but the
design of the cells and the accuracy required for
the measurement will also have to be taken into
consideration. All new cells should be thoroughly
cleaned before installation, and these cleaning
procedures depend on the design of the cell and
the electrode material.

Platinized electrodes Cleaning of these electrodes
constitutes a major drawback in their applica-
tion because no form of mechanical cleaning
Figure 17.2 Retractable conductivitycell. Courtesy, Kent should be attempted. A suitable cleaning solution
Industrial Measurements Ltd, Analytical Instruments. consists of a stirred mixture of 1 part by volume
isopropyl alcohol, 1 part of ethyl ether and 1 part
hydrochloric acid (50 percent). Alternatively, the
Measuring cells should be installed in positions
where they are adequately protected from sensitivity of the electrodes can frequently be
restored by immersion in a 1&15 percent solution
mechanical shock by passing traffic, dampness, of hydrochloric or nitric acid for about 2 minutes.
and extremes of temperature. Where a flow-line The electrodes should be thoroughly rinsed with
cell is connected directly in the electrolyte pipe, water before being returned to service.
suitable support should be given to the pipes to
ensure that the cell is under no mechanical strain,
and that the pipe threads in a rigid system are Annular graphitic electrodes Cleaning should be
straight and true. Dip pattern cells should be carried out with a 50 percent solution of water/
installed so that moving parts in a tank, e.g., detergent using a bottle brush. After thorough
agitators, are well clear of the cells. brushing with this solution, the cell bore should

- . ..

Molded Pipe
$reads

Figure 17.3 Flow-through cell. Courtesy Kent Industrial
Measurements Ltd. Analytical Instruments.