ECD and solvent compatability

[bob]

I have a question regarding the use of an ED-50A detector. The manual cautions against using a mobile phase that has greater than 30% methanol or 10% Acetonitrile. My question is what is the reason for this caution. I will use a mobile phase with 35% buffer and 65 % ACN to effect my separation at pH 5. Ther are no constraints on the column a polymer C18 with this buffer. The electrode is Pt working electrode and a Ag/AgCl reference. Is corrosion the reason.

Any ideas appreciated.

[AA]

Two things come to mind. Have you ever tried to measure the pH of a highly organic mixture? It doesn't work too well, similar thing here. Also, seems to me that there is a surface reaction with Au and/or Pt electrodes with ACN which reduces sensitivity and electrode lifetime over time. Those are just guesses on my part,y ou should put in a call to the supplier of that detector and get the tech support department to explain the cautions to you, after all, they wrote them.

[bob]

Thank you AA for the reply .I received some feedback from Dionex and it seems that the gasket used for the cell will eventually start to leak with these levels of organics. The long term solution will be to use disposable Pt electrodes and Teflon gsakets. First I will have to nail down the method.

[aceto_81]

One thing that comes to my mind:
If you use NaOH as post column addition, your mobile phase will be diluted, so you can go higher in organic concentration if you increase the flow of your post column reagent.

Good luck

Ace

[Jennifer Kindred]

Please consider also using the disposable electrode gasket (2 mil PTFE, PN 060141) with your non disposable platinum electrode. Disposable electrodes would be a good choice if you wish to avoid electrode polishing for each new set of experimental conditions during the method development.

Best regards,
Petr Jandik
Dionex