Hanna-instruments HI 903 Manual do Utilizador descarregar pdf (Página 133)

9-5

METHODS OPTIMIZATION

excess iodine will result in a steep drop in electrode potential which will be interpreted by the

HI 903 as an approaching endpoint. This will in turn result in the dynamic dosing algorithm

reducing the dose size until the excess iodine has time to react. The reduced dose size

effectively interrupts the titration and adds considerable time to the titration duration. The

titration will be interrupted repeatedly in this way such that the overall titration time is

longer, even though the value of the maximum dose size is set to a large volume. The

resulting titration curve will show:

Because reaction rates are faster with two-component reagents than those observed with

one-component reagents the maximum dose volume can be set slightly higher when using

two-component systems. In the case where the maximum dose is too low, titration time will

be extended.

9.1.1.3 Timed Increment

This setting controls the amount of time between successive titrant doses.

Setting the time increment appropriately is important to ensure that the titrant has adequate

time to mix with the sample such that the electrode measures a homogeneous solution

before the titrator makes the decision on the size of the next dose of titrant.

The value of the timed increment is dependent on the type of reagent system being used.

While the default value of 1 second is compatible for use with any reagent system, titrations

using two-component reagent systems can be expedited by decreasing the time between

successive doses.

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Hanna-instruments HI 903 Manual do Utilizador Página 133