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Effect of pH on Stationary Phase
Posted: Wed Sep 26, 2007 4:49 am
by Chandresh K. Soni
Hi to all
My Quearry is .
What is the Effect of Sample Solutions pH on the Polar and Non Polar GC Columns Stationary Phase with the temp.Programming.( Like 100% DimethylePolysiloxane , 5% Phenyle-95% DimethylePolysiloxane , 35%Phenyle-65% DimethylePolysiloxane , 14%Cyanopropyl Phenyle-84%DimethylePolysiloxane , 50% Phenyle-50% DimethylePolysiloxane)
Posted: Wed Sep 26, 2007 3:13 pm
by chromatographer1
Anything that is basic pH > 7 will quickly destroy a silicone based phase.
Organic acids generally do not harm silicones. Mineral or oxidizing acids will do harm and are not recommended.
Try not to use water with any silicone phase of any type.
best wishes,
Rod
Posted: Wed Sep 26, 2007 3:24 pm
by Chandresh K. Soni
Thanks for this
Actually My Sample is A Solution in Ethyle Acetate and Having Basic pH Near to 8-9.
We Found A Hump During Analysis. is It Due to Basic pH .or Due to Stationary Phase Problem.
My Column is DB-17 ( 50% Phenyle+50% Dimethyle Polysiloxane)
Posted: Wed Sep 26, 2007 5:50 pm
by chromatographer1
question?
why is the ethyl acetate basic? What base does it contain?
When I know that I can answer your question.
There should be no hump in ethyl acetate.
And a possible answer to your question:
It may be both if the first is true.......... since you injected your sample on the phase it may be damaged.
best wishes,
Rod
Re
Posted: Mon Oct 01, 2007 2:09 am
by Chandresh K. Soni
Thanks ROD
My Compound is a mix. of Sec. Amine + Valaraldehyde + Cyanohydrine Solution is Given in 20 % Ethyle Acetate or in 20% MeOH.
Posted: Mon Oct 01, 2007 12:32 pm
by chromatographer1
I suspect your 'hump' is a product of your interesting mix. Aldehydes almost always contain traces of the oxidation product (acid) which would be volatile but not chromatograph well ( a hump ). Aldehydes are also know to polymerize (dimer).
But it is most certainly possible that the secondary amine could have (could be reacting) reacted with the fused silica surface or silicone phase.
I suspect the former is more likely than the latter.
Like Bruce says........ Keep having fun.
Rod
Posted: Mon Oct 01, 2007 8:37 pm
by Alchemist5
Try not to use water with any silicone phase of any type.
I've always believed this (initially starting out in the environmental field). However, once entering the pharmaceutical field I've found that the USP loves injecting water (either by headspace vapor or direct inject) into 624 phase (G43) columns. Good ol' USP <467> is mainly written towards water soluable materials.
How long does it take to eventually destroy the phase in one of these columns with, let's say, 10-15 water headspace injections (1mL) a day?
Burt