Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 121

heights pre-fixed by the user for the sample, standards and blanks, is collected. The
program features a subroutine for the optimisation of each system. The program also
allows data to be discarded from anomalous peaks or standards that would give a low
correlation coefficient for the linear range of the calibration graph. This corresponds to
the change in the width (∆ t ) at a height h as a function of log C (C= analyte
concentration).
Alkalinity is measured by titration with hydrochloric acid to the methyl red endpoint.
Similar to a conventional titration, the reaction is monitored after the equivalence point
so that the blank signal (distilled water) shows a higher peak width. The greater the
alkalinity, the smaller is the peak width. The analytical signal was so that
the slopes of the calibration graphs were positive. To determine total ionic concentration
the salts present in the water sample are transformed into their corresponding acids on
passing through the cationic resin in the H + form. The acids are then titrated with sodium
hydroxide and phenolphthalein. In this method the minicolumn is placed in the loop of
valve S ′ (Fig. 2.8) which is inserted into the circulating stream in the emptying position.
In the filling position, the minicolumn is regenerated with a sodium hydroxide stream
and washed with distilled water, thus allowing continuous use for 4-5h.
The reaction is monitored at 552nm (after the equivalence point in the conventional
titration) so that, as in the above system, the peak width is wider for the blank than for the
samples.
As the insertion of a glass calomel microelectrode into the flow injection analysis
configuration introduced no species that disturb the system, pH monitoring can be readily
carried out by inserting the sensor prior to the reagent injection (Fig. 2.8) and calibrating
it with standard buffer solutions at the working flow rate.
Table 2.5 summarises the features of the simultaneous determination of alkalinity, pH
and total ionic concentration.
Workers at Tecator Ltd have published flow injection analysis methods for the
determination of total alkalinity [156] in non saline waters. In this method the sample
zone is merged with an acidic bromocresal green reagent (Fig. 2.10). Depending on the
amount of acid consumed, the indicator changes its colour from yellow to blue.
Fig. 2.10 Flow injection manifold, determination of total alkalinity
Source: Reproduced with permission fromTecator Ltd [156]
Table 2.5 Features of the simultaneous determination of pH, alkalinity and total ionic