Anions in seawater - Determination of Anions in Natural and Treated Waters - page 358

3.1 1 Carboxylic acids
3.11.1 Ion chromatography
The application of this technique is discussed in section 12.3.1.
3.12 Chloride
3.12.1 Titration method
Chloride at the percentage level, as occurs in sea water, is usually determined by classical
titration procedures using standard silver nitrate as the titrant and potassium chromate
indicator or alternatively by the mercuric thiocyanate procedure using dithizone as
indicator. As large dilutions of the original sample are involved in these analyses it is
essential to use grade A glassware and take all other suitable precautions, such as
temperature control in these analyses.
Chloride can also be estimated by potentiometric titration using standard silver nitrate
[27]. The results are recorded directly on punched tape and by teletyper and evaluated by
means of a computer program based on the Gran extrapolation method. The
determinations have a precision of ±0,02% and since many samples can be titrated
simultaneously, the time for a single determination including evaluation and editing of
titration data can be reduced to less than 5min.
Jagnuer [28] has also described a semi-automatic titration for the precision
determination of chloride in seawater. This titrator supplies pre-set increments of titrants,
and has a direct teletyped read-out system on punched tape suitable for subsequent
computer treatment of the titration curve. It has been used for the potentiometric
determination of total halides (silver electrode), and of alkalinity (glass electrode) and for
the photometric titration of total alkaline-earth metals, in seawater. Several titrations can
be effected simultaneously.
Grasshoff and Wenck [29] have described a version of the Mohr-Knudsen silver nitrate
titration procedure for the determination of the chlorinity of sea water. In this method,
which overcomes the disadvantages of conventional burettes, use is made of a motor-
driven piston burette of 20ml capacity, which is sufficient for the range of chlorinites 0 to
45 per thousand. The accuracy is the same as for conventional titration. The apparatus is
compact and portable.
Several autoanalyser procedures are available for the determination of chloride.
3.12.2 Ion selective electrodes
Noborn [30] has studied the dynamic properties of chloride selective electrodes and their
application to sea water concentrates. An Orion 94-17 electrode was used in these
studies.
In the presence of bromide ions the electrode was subject to a drop in potential (eg 1.5