problem with background noise

[lab tech]

Please help,

I am usning Dionex ICS 3000 with a conductivity detector and chemical suppression. Prior analysis I washed the system with two washing solutions 50 mM sodium citrate for 15 min with 1ml/min and 150mM of NaOH for 15 min also with 1ml/min. I purge the line with my mobile phase and let the system to equlibrate. My problem is a massive total signal from the detecor = 15 micro Simens.

What should I do next?

Thank you in advance for all your help.

lab_tech

[tom jupille]

Check the system documentation and re-run the performance qualification (PQ) on the suppressor + detector.

[lab tech]

Thank you Tom

[Mark Albertson]

Hi Labtech,

The clean up solutions you have used are strongly Ionic, particularly the citrate ion in your clean up phase, this is an extremely polyvalent ion and binds strongly to most anion exchange columns. It could in fact require an overnight purge with your strong base solution to elute any residual citrate from the column. My second question is did you run this clean up procedure with the suppressor in line? You should always by-pass the suppressor when using any clean up solutions with columns. If you did not adjust your suppressor current setting to accommodate the higher ionic strength of your eluant then the chances are you have also converted the membranes from their Hydronium form into its Sodium form, resulting in reduced analyte responses. Please read the trouble shooting section of your suppressor manual and follow the instructions in the section entitled small analyte responses. Finally I would assume this model of ICS-3000 is not equipped with RFIC and an EG eluant generator? If it was and you ran citrate thought the EG and particularly the CR-ATC, you must be aware this device has an anion exchange resin in it, which is designed to remove small analyte contaminants from your MilliQ water. If this device was in line the chances are it is still loaded with citrate which will leach off this device for quite some time. The best remedy is to consult the CR-ATC manual and run 400mM NaOH clean up procedure. Remember with strong Base or Acid clean ups for columns in particular all devices should be cleaned up separately (i.e. guard columns should not be in series with separator columns to avoid contaminants flowing from the guard and lodging on the higher capacity separator) and in all cases the suppressor and conductivity cell should be removed from the flow path.

[lab tech]

Dear Mark,

Thank you for your reply.

I run the clean up procedure with suppressor in line without adjusting the current, and the ICS-3000 I am using is not equipped with RFIC and an EG eluant generator. I will clean my column and guard column separately with a strong base solution. I will also check a suppressor manual for trouble shooting section regarding small analyte responses.