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Replace ammonium hydroxide with sodium hydroxide

http://www.chromforum.org/viewtopic.php?t=4740

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Replace ammonium hydroxide with sodium hydroxide

Posted: Tue Oct 10, 2006 12:57 pm
by WK
Hi All
I have no ammonium hydroxide so I am running C18 column 150mm x 4mm x 3.5um with 20mM H3PO4 to pH 3.6 with sodium hydroxide. The gradient is 10% to 40% acetonitrile over 10minutes.
Are there any problems associated with using sodium hydroxide in mobile phase?
UV is 210nm.
I seem to get some mixing problems and high baselines sometimes.
WK

Posted: Tue Oct 10, 2006 3:01 pm
by rhaefe
May I ask why you are running at pH=3.6? The three pKa of phosphoric acid are 2.1, 7.0 and 12.3.
For straight forward RP separations it should make no difference if the counter ion is sodium or ammonium.


cheers

Posted: Tue Oct 10, 2006 5:40 pm
by Uwe Neue
In the range of acetonitrile in which you are working there is no solubility problem with either salt. However, you may need to flush the column with water before putting it into a storage solvent.
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