Xylem SI Analytics TitroLine 7800 Gebrauchsanleitung Seite 197

4.6.2.3 End-Point titration
The goal of End-Point titration consists in titrating as precisely as possible to an end point given in terms of pH,
mV or µA. In the case of pH und mV you can also titrate to two end points. Consumption in the end point will be
used as a result.
The classical examples of pH End-Point titration include total acidity in wine or beverages and the p+m value
(alkalinity). A classic example of µA End-Point titration is present in the determination of sulphurous acid (SO
wine and beverages.
The first stage of End-Point titration consists in the continuous dosing up to a delta value away from the set end
point. The dosing speed can be adjusted. Subsequently, titration is performed in a drift-controlled manner with
linear step sizes between the delta value and the end point.
Example (Fig. 102): Determination of the alkalinity (m value)
pH in the point:
delta pH value:
linear step width:
dosing speed:
End-Point delay:
drift:
Up to a pH value of 5.50, titration is performed with the set dosing speed. Subsequently, the method will change
to a linear step size of 0.02 ml, until the end point of pH 4.50 is either reached or fallen short of. Should this value
raise again to above pH 4.50 within 5 seconds, another titration step of 0.02 ml will be added. Consumption will
be determined precisely at pH 4.50.
Fig. 102
4.6.2.4 pH Stat Titration
The pH Stat Titration is a special form of the pH endpoint titration, which takes place in two different stages.
In the first stage, the desired pH value is first titrated and the pH value is kept constant over a set time during the
second stage.
In the first stage, the TitroLine
value is drift-controlled during the last phase before the endpoint or taken over as usual at a fixed delay. In this
phase, additions were made by titration at linear increments. But once the desired pH is reached, it is
immediately switched to the second stage, the actual pH-Stat level. This means that the drift control is now
omitted and a fixed waiting period of "zero" seconds occurs between the titration stage and the measurement
value acquisition. This is also necessary; otherwise you could not maintain the pH value over a set period in
many cases.
4.50
1.00
0.02
12 %
5 s
medium (25 mV/min)
®
7800 acts just like a normal pH endpoint titration (see above). That is, the pH
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