By Rolls T. on Monday, February 23, 2004 - 01:17 pm:
Hello Folks!
Can any one tell the role of Na2SO4 as additif in mobile phase. In which case it can be recommended to use it?
Thanks
By A.Mouse on Monday, February 23, 2004 - 06:30 pm:
If you are talking about reversed-phase, it does nothing significant, and therefore is fairly useless.
By HW Mueller on Monday, February 23, 2004 - 11:09 pm:
With macromolecules (proteins...) it may have a pronounced effect, connected with ionic strength and the phenomenon of lyotropy, chaotropy. If concentrated enough it is quite lyotropic and will increase retention on RP. (One should never forget, at low concentration, if I remember correctly near 0.1 M, it is chaotropic and will tend to keep the protein in the mobile phase, relatively...).
By Rolls T. on Tuesday, February 24, 2004 - 04:14 am:
My question aroused from a paper where aminoglycosides are analyzed on reversed phase columns as well as on polymer columns (PSDVB) and a use of Na2SO4 was made.
By A.Mouse on Tuesday, February 24, 2004 - 03:43 pm:
On samples as polar as this, it may serve as a salting-out medium.
HW is also right. I dismissed it a bit too rapidly.
By Anonymous on Wednesday, February 25, 2004 - 12:44 am:
Sod sulphate also used in chromatography of highly polar organic acids like hydroxy citric acid in reversephase and work well.
By Anonymous on Wednesday, February 25, 2004 - 07:23 am:
Dear Anon, what happens with Na2SO4 and polar organic acids?
By Chris Pohl on Friday, February 27, 2004 - 12:03 pm:
The purpose of sodium sulfate in the application mentioned above, is to reduce the solubility of the analyte in the mobile phase. "Salting Out Chromatography" has been used for many years as a means of improving retention of polar analytes. This technique was later renamed HIC by the biologists but the principle is the same. By choosing highly hydrated ions such as sodium and sulfate and using substantial concentrations, this significantly reduces the amount of water available for solvation of polar organic molecules. Actually, there are other salts which will work better such as lithium sulfate in terms of their efficiency in tying up water molecules but sodium sulfate is cheap and available in fairly good purity so it's more commonly used for this application.