by
cari » Fri Nov 11, 2011 4:51 pm
MauriceS wrote:
Dear Fellow chromatographists,
Here is the thing. After 2-3 injections that run smoothly, the following happens: The current will spike to a normal level for a few seconds and then it falls down to between 0.5 and 2 µAm.
Any idea what is happening? Is the capillary insufficiently filled with run buffer, or is something else happening?
Hi Maurice,
It is always hard to troubleshoot on paper. Questions that come up are:
Did this application ever run properly, or have you had these problems all the time?
As suggested by others, at the look of it, there seems to be air or gas in your system, or some blocking. What is the sample matrix? Anything in it that could behave strange with borate or at high pH? Are the capillary ends cut straight? The rinsing times seem long enough. What is your current if everything goes well, and how does you current profile look then? IF it is a high current, you might be generating more heat than you'd like. At the pH you are working on, some gas may get out of the system when you apply the voltage and heat up. Do other, well-known applications work well? What water do you use for the BGE. we once had a problem with our MilliQ system in the lab, without knowing it. The resistance of the water was still OK, no extra currents, but the water turned out to be saturated with air, which can out in tiny bubbles once in the CE (30 degrees at that time, 10 degrees above lab temperature), giving all kind of weird problems we never had before. Degassing (He, boiling) helped.
It's been some time since you posted this, so I wondered whether you still have this problem, or whether it "just disappeared"?
/Cari Sänger
www.kantisto.nl