4 Description of function
K-375 / K-376 / K-377
Operation Manual, Version E
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with the measurement. Colorimetric titration requires daily determination of the setpoint.
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Titration Mode
Standard
In the standard mode the distillation and titration are performed sequentially. First the distillation is
completed then the titration starts.
Online
In the online mode the titration starts while the distillation is still in progress. The start time of the
titration depends on the pH value and is determined automatically. It helps optimize the speed of
measurements as it saves time.
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Measuring Mode
Startpoint pH
The device measures the pH of the boric acid before the distillation is started and uses it later on as
enpoint for the titration. When startpoint titration is used, the pH must not be adjusted to 4.65, but it
must be between 4.4 and 5.0.
Endpoint pH
The set value, normally 4.65, is used as endpoint for the titration. The boric acid has to be adjusted
to pH 4.65 before starting sample measurements. This mode is more accurate and yields the highest
accuracy.
Setpoint mV (colorimetric)
The setpoint must be determined daily before the blank values and samples are colorimetrically
tested, and in addition, if the distillation time, the boric acid, the indicator or the titrant is changed. The
setpoint determined is then used as the end point for the subsequent colorimetric titrations.
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Titration Algorithm
Normal
This algorithm is the most accurate one and is recommended for samples with low nitrogen content
(below 1 mg) and for the use of highly-concentrated titration solutions (e.g. 0.5 N acids).
Optimal
The best ratio between accuracy and process speed is achieved with this algorithm.
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Determination Mode
Standard
In the majority of cases it is necessary to digest samples to make the nitrogen accessible to steam
distillation. Whenever digested samples are analyzed the standard determination mode is used.
Direct Distillation
A small number of applications allow freeing the nitrogen via direct steam distillation without requiring
a digestion. In such a case the direct distillation mode needs to be activated.