8 Troubleshooting
K-375 / K-376 / K-377
Operation Manual, Version E
147
Problem
Cause
Corrective measure
Nitrogen content too low
∙ Incomplete digestion
∙ Insufficient H
2
SO
4
∙ Kjeldahl Tablets and H
2
SO
4
in
wrong ratio
∙ Nitrogen content per sample
tube is too high
∙ Not enough NaOH or incor-
rect concentration of NaOH
used (required is 32 %)
∙ Leakage during distillation
∙ Leakage during digestion
∙ Wrong titrant used
∙ Defective pH electrode
∙ Defective colorimetric sensor
∙ Dirty glassware
∙ Air bubbles disturb the colori-
metric titration
∙ Increase digestion time
∙ Increase volume
∙ Correct ratio
∙ Not more than 200 mg
Nitrogen per sample tube
∙ Correct volume until color
change is visible
∙ Check and tighten, check
connection between
condenser and splash
protector, replace seal if
required
∙ Check sealing and scrubber
suction capacity
∙ Check and correct
∙ Calibrate electrode, replace if
necessary
∙ Clean the sensor surface,
place the sensor in cleaning
solution during idle periods
∙ Only use clean glassware
∙ Check the top fitting on the
condensate inlet
