Table of Contents
Advertisement
5
– Troubleshooting Guide
5.3.6
Large Baseline Dip in the Chromatogram
A large baseline dip appearing later in the chromatogram is usually caused by oxygen in the
sample injected. The 'oxygen dip' is normal and can be reduced in magnitude with higher KOH
concentration in the eluent.
5.3.7
Unidentified Peaks Appear with Expected Analyte Peaks
During a potassium methanesulfonate/ potassium hydroxide gradient, a number of small peaks
may appear. These peaks are usually due to trace contaminants in the water supply. The
contaminants accumulate on the column during the isocratic section of the chromatogram and are
released, frequently as irregular baseline deformations or sharp spikes, with the increasing eluent
strength.
If extraneous peaks are observed even after the water supply is excluded as a possible cause, clean
the auto sampler lines and sample loop. The auto sampler should be cleaned using the following
protocol:
A. Disconnect the column and detector cell from the auto sampler.
B. Set the pump to 100% deionized water.
C. Place the following solutions in the auto sampler and inject in sequence. Use 25 µL full
5.3.8
Decreased Detection Sensitivity
Always confirm the loss of response by performing at least one injection of the system suitability
standard mix as described in Section 4.1. This is to make sure that a decreased level of response
is not being caused by system problems.
Any decrease in detection sensitivity means that the working electrode surface has been affected.
The operator should install a new working electrode. Spare gold working electrodes should always
be available in order to avoid unnecessary delays.
Exceptions:
Check the pH reading. If the value is out of range or >13.2, install a new reference electrode and
then install a new gold working electrode. The system cleanup is not necessary. The decrease in
sensitivity was caused by a gold-oxide-buildup on the electrode surface because the reference
potential was too high.
Peak heights will increase with increasing eluent concentrations. This is due to improvement of
the kinetics in the electrode detection related to ionic strength and pH effects. If you run the same
standard at 1mM and at 12 mM, peak heights will increase at 12mM. Hence you will see a
decrease in peak heights whenever going to lower eluent concentrations as well.
Thermo Scientific
065734-01
loop injections:
1.
1 M NaOH
2.
Deionized water
3.
IPA
4.
Deionized water
5.
1 M HCl
6.
Deionized water
Product Manual for CarboPac PA200 Columns
For Research Use Only. Not for use in diagnostic procedures.
Page 32 of 37
Advertisement
Table of Contents
