BUCHI KjelSampler K-377 - Manual (Page 145)

8 Troubleshooting
145 K-375/376/377 Operation Manual, Version B
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 incorrect
concentration of NaOH used (required
is 32 %)
• Leakage during distillation
• Leakage during digestion
• Wrong titrant used
• Defective pH electrode
• Dirty glassware
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 connec-
tion between condenser and splash
protector, replace seal if required
Check sealing and scrubber suction
capacity
Check and correct
Calibrate electrode, replace if neces-
sary
Only use clean glassware
Poor repeatability • Air bubbles in titration system, buret,
tubes
• Aspiration not working properly
• Incorrect or no pH electrode calibra-
tion
• Sample inhomogeneous
• Sample weighing problems
• Incomplete digestion, digestion time
too short
• Suction capacity during digestion is
too strong
• Stirrer is not working
• Dip tube blocked, loose, too short or
defective
Fix tubing and refill buret
Check for leaks and fix
Calibrate electrode with fresh buffer
Homogenize sample
Use weighing boats to improve
procedure
Check color of samples during
digestion and choose digestion time
accordingly
Reduce suction power at the
Scrubber with the bypass valve
Clean the stirrer, replace if necessary
Check and correct