Analytical Chemistry

Applications of Coulometric Titrations

The coulometric generation of titrants is widely applicable to redox, precipitation, acid-base and
complexing reactions. Of particular value is the determination of many organic compounds with
bromine and of mercaptans and halides with the silver ion. Amperometric equivalence point detection is
the most common. An attractive feature of the technique is that the need to store standard and possibly
unstable reagent solutions is obviated. In fact many applications involve the use of electrogenerated
reagents such as halogens and chromium(II) which are difficult or impossible to store. The technique is
especially useful for the determination of very small amounts, i.e. in the microgram or nanogram ranges.
Relative precisions of 0.2–5% can be attained at trace levels, which is better than most other titrimetric
procedures. Some examples of titrations with electrogenerated titrants are given in Table 6.5.

Table 6.5 Applications of coulometric titrations at constant current

Element or compound

determined

Titrant generated Means of equivalence point

detection

Example of application

Water

(Karl–Fischer reagent)

amperometric organic solvents, petroleum

products

Cr, V Fe2+ amperometric steels, oils, asphalt

Ag I– amperometric lubricating oils

phenols, olefins Br 2 amperometric petroleum products

thymol Br 2 amperometric herbs

mercaptans, chloride Ag+ amperometric fuels

aromatic amines H+ potentiometric organic chemicals

oxygen Cr2+ amperometric seawater, gases

6.4—

Conductometric Titrations

Summary

Principles

Measurement of the conductance of an electrolyte solution using an ac source. Rate of change of
conductance as a function of added titrant used to determine the equivalence point.

Instrumentation

Platinum electrodes; low-potential ac source; conductance bridge.

Applications

Acid-base titrations, especially at trace levels. Relative precision better than 1% at all levels.