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questions about the effect of acid on the C18 HPLC column?
Posted: Wed Oct 05, 2005 10:48 pm
by shawshark
I know the reasonble PH range for the HPLC column is 2-8.
if no buffer in the column and strong acid injected into the column,what bad consequence will happen to the column?
the silica stationary phase will be fully protonated? then what ? the retention will be affected? how?
Thanks for any comments.
Posted: Wed Oct 05, 2005 11:12 pm
by tom jupille
Unless you're injecting huge volumes, the effect on the column is likely to be minimal. Assuming an inorganic acid anion (nitrate, chloride, etc.), the low pH region should wash right through the column unretained.
The effect on the chromatography will depend on the chemistry of your analyte(s). If they are basic, then you may see some strange peak shape effects as they convert from the cation (protonated) form to the free base (neutral).
Posted: Thu Oct 06, 2005 1:01 am
by Bill Tindall
You didn't provide enough information to get a confident response. What is the acid, concentration, column temp, buffered eluant?
Acid will promote the hydrolysis of the Si-O-C bonds that attach the bonded phase to the silica. I would expect that 50 uL of 1 M sulfuric acid might have a noticable effect after a few dozen injections. Is this what you had in mind?
On the other hand if the acid was HCl you would probably elute some stainless steel.
Is the mobile phase buffered? The buffer might neutralized what ever acid you injected.
Posted: Thu Oct 06, 2005 1:07 am
by shawshark
Thanks for the comments.
Yes, I forgot to mention that it is the perchloric acid with the concentration 0.1 M, 10µL each injection, three repeated injection totall, and no buffer in the column ,the mobile phase is just the water.
Column diameter: 2 mm
column type: ODS (C18), 5 µm porous bonded silica packing
Volume fraction of the mobile phase: 0.7
Posted: Thu Oct 06, 2005 11:19 pm
by Bill Tindall
that is getting to the point where I would be concerned, but really my concern is just a guess. If I was doing 2.5 mL/min, mostly water, and the column had already paid for itself I would probably shoot it. On the other hand, if I was feeling cautious, I would neutralized most of the acid with some base, eg few uL of conc. ammonia, and then shoot it. Perchloric acid solutions will be a stronger acid in methanol or acetonitrile than in water. Remember that potassium perchlorate is insoluble, for better or worse.