BUCHI KjelSampler K-377 - Manual (Page 37)

4 Description of function
37 K-375/376/377 Operation Manual, Version B
4 .5 .5 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. If the boric acid used as receiving solution is not adjusted to pH 4.65 the
startpoint mode is recommended.
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.
4 .5 .6 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.
4 .5 .7 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.