Chromatography Forum

because the detection was set at low wavelength which is the highst absorption of my analyte , at this i see the oxygen peak which come from methanol and i can tell you for sure this is oxygen peak and i am using isocratic . Many papers say at this low wavelength using methanol you will see oxygen peak very high but is it acceptable to just keep it in the middle or no i have to put it before the two ?

any help i will appreciated thanks

What I was taught years ago when the online degassers aren't as good are they are today was to degass first with either helium sparge or vacuum degassing, then use the online degasser to maintain the degassed state of the solvents. Seemed to work pretty well then, at least I didn't have to wait as long for the baseline to stabilize after the online degasser was turned on.

As an interesting side note, one time a former coworker was "helium" sparging his solvents, left the gas turned on overnight, and the next morning we discovered an empty cylinder, which had been filled with hydrogen!

Newchr., you are using continuous mixing of an aqueous solution and Methanol and see an oxygen peak? How?? You still didn´t tell us how you know that this is oxygen.

Newchr., you are using continuous mixing of an aqueous solution and Methanol and see an oxygen peak? How?? You still didn´t tell us how you know that this is oxygen.

Well HW, i followed the book of TRoubleshooting that is mentioned by Tom , and i am sure during one year work it is oxygen peak because when i use acetonitril it doesnt come , so do u thing if can be in the middle this peak will this be acceptable ?

Thanks Hw , ireally appreciate ur help

Obviously, if your peak does not interfere with your analytes you can ignore it if you are sure that it is repeatable. If it were an oxygen peak you could not be sure that it comes at the same time all the time. So you should know some more about this peak.
From what I know so far it can not be oxygen, first of all where does the oxygen come from and why should it peak out in an isocratic technique? Now, I can imagine that you can introduce an air peak with your sample injection, if you use oxygen to concentrate the sample maybe you can even introduce an oxygen peak, but from what you tell us I dont see this. Also, if the peak is absent when acetonitrile is used (as mobile phase, isocratically?) doesn´t tell me anything considering the sparce info you give.