Metrohm 754 Dialysis Unit - Manual (Page 32)

4.1 Malfunctions and their rectification
754 Dialysis Unit
29
4 Malfunctions – Maintenance
4.1 Malfunctions and their rectification
If difficulties appear with the IC system during analysis, their cause are
best investigated in the order separating column → → pump → → eluent
→ → IC system. An overview of possible malfunctions, their causes and
remedies can be found in the instruction manuals of the 732/733 IC
System (section 5.3.2). In addition to these general malfunctions the
table below contains others which might arise as a result of the opera-
tion of the 754 Dialysis Unit.
Malfunction Possible causes Rectification
Insufficient or non-
existing flow rate at
754 Dialysis Unit • Contact pressure too low
• Pump tubing faulty
• Inlets to dialysis cell blocked
• Sample tubing blocked by
particles that are too large
• Bacterial growth in the sample
channel and dialysis cell
• Overly narrow PTFE tubings due
to excessive tightening of the
compression fittings
• Set contact pressure correctly with contact
pressure lever (see section 2.3.3).
• Replace pump tubing
(see section 4.2.5).
• Replace the dialysis membrane and clean
the cell (see section 4.2.6).
• Replace blocked tubing; always centrifuge
samples (see section 3.3.7).
• Periodically replace tubings 26 26, 30 30, 33 33 and
45 45 for the sample channel; replace the
dialysis membrane
• Replace tubings.
Leakage • Leaking compression fittings • Tighten the compression fittings or replace
if necessary.
Air bubbles in pump
circuit • Suction tubing is not immersed
• Leaking compression fittings
• Acceptor solution insufficiently
degassed
• Standing air bubbles
• Ensure suction tubing is fully immersed in
the acceptor or sample solution.
• Tighten the compression fittings or replace
if necessary.
• Re-degas the acceptor solution.
• Small air bubbles are not a problem. If big
air bubbles occur, rinse the sample chan-
nel with degassed acceptor solution (open
outlet briefly if need be).
Insufficient yield from
dialysis • Transfer time incorrectly set
• Dialysis time too short (e.g.
when concentration is too low)
• Dried out or damaged dialysis
membrane
• Deposits on the dialysis mem-
brane, recognizable from dis-
colouring at the sample inlet
• Unsuitable dialysis membrane
• Check optimum transfer time, especially
after each change of membrane or tubing
(see section 3.3.4).
• Check optimum dialysis time (see section
3.3.5).
• Replace dialysis membrane
(see section 4.2.6).
• Replace dialysis membrane
(see section 4.2.6).
• Use different dialysis membrane.