Hello,
first, we should clarify whether the poor reproducibility is due to random fluctuations or if it is caused by a trend in response. Constancy and accuracy of pump flow rates should also be verified. Even the handling of standards and samples should be reviewed. Without additives, all concentrates should be stored frozen and all dilutions have to be prepared fresh daily. I am assuming you are using the recommended "quadruple potential" waveform.
Random fluctuations would point to problems with sampling, e.g. autosampler malfunction.
Uniformly trending results would indicate a need to service the detector cell. Please confirm the trending by at least 5-10 injections.
Two parts of the detection cell needing service most frequently are:
reference electrode (RE)
working electrode (WE)
The first sign that something may be wrong with the RE is a missing pH readout in detector screen 2 when running NaOH eluents. The missing readout is caused by a shift in Ag/AgCl potential causing the pH reading to be out of range. A new reference electrode needs to be installed.
If the RE can be excluded as a possible cause, turn your attention to the WE. An ideal tool in trouble shooting WE problems are disposable gold electrodes (P/N 060139). Each six pack of those electrodes contains a test chromatogram with the specified size of peak areas for the most common carbohydrates.
With a new disposable electrode or with a freshly polished non disposable one, the response should as specified and reproducible.
If it is not so, please call a Dionex service representative.
Hope this helps,
Petr Jandik
Dionex
Sunnyvale, CA
.