BUCHI ELS Detector C-650 - Manual (Page 46)

C-650 Operation Manual, Version B 8 Troubleshooting 46
8.3 Perform the noise test
Repeat the tests described in section 5.9 and compare the observed data to the results that
were obtained when the unit was initially installed. These tests can be very valuable to isolate the
problem.
As an example of this point, if the Electronic Noise test (section 5.9.2), Background Noise test
(section 5.9.3) and Solvent Noise test (section 5.9.4) provide results that are similar to that ob-
tained when the unit was initially installed, but the Column Noise test (section 5.9.5) provides a
significantly different value than what was obtained at installation, it is likely that the problem is in
the column (e.g. highly retained compounds are being eluted).
8.4 Specific detector troubleshooting
• The mist from the nebulizer should be homogeneous. If it is not homogeneous, the nebulizer,
the needle or the PTFE tube may be partially obstructed. To remove the obstruction, pump a
solvent that can dissolve the foreign material. As an alternative, the nebulizer can be placed
in an ultrasonic bath to dissolve the foreign material. Instructions about cleaning of the nebu-
lizer are presented in section 8.5.
Do not disassemble the nebulizer. Disassembling the nebulizer will destroy it and this will void
the warranty.
• If the sensitivity of the detector is low, ensure that there are no leaks in the system. Make
sure you are using a fresh sample and consider running the test using a back pressure loop
instead of a column. Alternatively, the LED may need to be replaced or the nebulizer could
be obstructed.
• If the noise test did not show that the problem could be caused by the application or the
system, a decrease in the sensitivity is often caused by the nebulizer (main cause). Clean the
nebulizer as described in section 8.5. If the sensitivity does not return to normal, the nebu-
lizer might need to be replaced. Please note that the root cause might also be in different
module, i.e volumes injected might be too low or dead volumes in capillary connections may
cause peak broadening.
• If the detector signal is saturated or if there is a decrease in the dynamic range of the
system, it is possible that a residue is passing through the detector cell: this will lead to an
intense signal due to a significant amount of light-scattering. This residue may be a result of
the elution of strongly retained materials from the column, or may come from the solvent. To
determine the cause of the problem, bypass the column and observe the signal intensity:
• If the signal returns to normal, strongly retained materials are eluting from the column.
Flush the column with a strong solvent to elute all material.
• If the signal does not return to normal, the solvent contains a too high residue material,
after evaporation and is not suitable for use with the detector.
• If the noise of the detector without solvent is high or if ghost peaks occur, it is possible that
foreign material is present in the drift tube. In this situation, increase the temperature to
100 °C and pump solvent at the rate of 2 mL/min, using a gas pressure of 2 bar (29 psi).