By A. Chemist on Monday, March 4, 2002 - 08:35 am:
Just wondering if anyone can tell me something about heptane that may be causing my mobile to turn cloudy. Twice from fresh bottles, I have noticed a slight cloudiness developing over time which I cannot locate the source of. The heptane is used isocratically and degassed before use. The bottles are not covered with parafilm, and all glassware has been ruled out. Would moisture from the air be a factor? how does water act in heptane? I presume it sepatates into layers as apposed to a cloudy appearance?
Any ideas??
Thanks in advance
By Will on Monday, March 4, 2002 - 10:32 am:
We had all manner of problems using hexane.
As the vast majority of systems sold are to be
used reverse phase the rubber/plastic parts
are sometimes not stable to the more
non-polar solvents. Could it be that the lines
going in to the heptane (presumibly plastic)
are degrading?
Will
By Anonymous on Tuesday, March 5, 2002 - 11:29 am:
I use heptane/IPA mobile phase all the time and have never seen that problem. I seriously doubt that trace water would cause the haziness.
By MikeH on Monday, March 11, 2002 - 02:31 pm:
Agreed, check the materials that you are using for tubing to draw the solvent or anything else that it contacts.
What are you using to degas? Hopefully not the same set-up as others are using to degas their reverse phase mobile phases!!! Or are you running through a membrane degasser? I have seen problems with these and normal phase reagents (once again, designed for reverse phase).
How much time are we looking at here? Over night or over a week?
And I am also making the wild assumption that you are not recycling your heptane mobile phase (hey, I gotta ask just to be sure...no offense meant).
By maris on Saturday, March 16, 2002 - 09:02 am:
We are working a lot in NP mode with hydrocarbons as mobile phase( also with hexane - manufacture J.T.Baker) and the mentioned phenomena never has been observed.
Dr.A.Weisman
By A. Chemist on Wednesday, March 20, 2002 - 11:19 am:
It may have been the solvent inlet tubing which is plastic. I presume the alternative is peak/Steel or is there another alternative?
Not sure if the analyst recycled the mobile while equilibrating but i presume this is ok once the column has been washed through a few times to clear the packing solvent or is there something again I don't know about heptane and LC?
Thank you all for the useful info
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