EDTA in mobilephase
Posted: Tue Oct 06, 2015 12:34 pm
by eb3
Is there any effect of EDTA on column chemistry or active sites? 85% water 15% methanol with 5mMol EDTA, C18 250 x 4.6mm 4µm
Columns are quickly losing resolution and observing poor peak shape on various impurities after only couple weeks worth of analyses.
Re: EDTA in mobilephase
Posted: Tue Oct 06, 2015 4:01 pm
by tom jupille
First of all, how many samples is "a couple of weeks' worth"? And what is the pH? If your samples are junky, then you might be lucky to get a couple of hundred injections per column.
The sure way to tell is to start with two columns. Run a check sample in column "A" and then put it on the shelf (leave your EDTA buffer in there). Run column "B" for your usual couple of weeks until you can see a noticeable deterioration, then hook up column "A" and re-test it.
If column "A" still looks OK, then the problem is contamination from your samples. If it looks about the same as column "B", then it is, indeed, deteriorating. If your buffer is at pH 8, then you are at or above the operating pH of many bonded-phase columns, and a short lifetime is normal. There are columns that will go above pH 8, and the vendors aren't shy about promoting them, so check with your column vendor of choice for their recommendation.
Re: EDTA in mobilephase
Posted: Tue Oct 06, 2015 6:39 pm
by eb3
pH is under 7 and 4 to 5 i am thinkin. will check this.
One problem is the stability of sample solutions. It is a prep and shoot and keeping a sample over a few hours is not feasible. We have probably got about 100 injections before issues arise. New column did show promising results only to go downhill quickly.
I like the suggestions of a check sample and that made me think to look at what is going on with the samples and currently not being filtered. thanks for suggestions. will keep chugging along.