By Anonymous on Monday, June 21, 1999 - 12:42 pm:
I am aware that high concentrations of buffers and/or salts can cause physical damage not only to the column, but to the instrument as well. However, how high is TOO high? If proper care is employed afer running samples (flushing system with high water content for a couple of hours), what are the limitations? Our buffer consists of NaH2PO4 and 1-Octane Sulfonate. Is precipitation of the salt when mixed with different organic solvents the only real concern? Any input concerning this matter would be greatly appreciated.
By SRS on Wednesday, June 23, 1999 - 02:40 am:
Washing the system after with water REALLY helps. I found that if ytou are running high conc. of buffer and you change directly ACN right away, you buffer will precipitate out and usually shut down your system due to high pressure.
By Tom Jupille on Wednesday, June 23, 1999 - 10:35 am:
Precipitation is a very real problem. Also beware of the long equilibration time problems that can occur, especially with C18 columns. Check the thread on "Washing column with 100% aqueous" in the archives. When we teach the troubleshooting course, we usually recommend buffer-free mobile phase (i.e., organic+water only) to avoid both problems.
-- Tom Jupille / LC Resources Inc.
By BuckHeel on Wednesday, June 23, 1999 - 11:47 am:
Tom
Following your comment, a question comes to my mind since we are also currently running several buffer methods. What do you suggest for keeping the pH stable at ca. pH 7 without buffers?
Peace
By Imre Molnar (98-internet-fuer-berlin-bei.online-now.de - 195.211.16.98) on Friday, July 16, 1999 - 04:01 pm:
There is no way to have stable conditions at pH 7 without the use of buffers, if you have -COOH or amino-groups - here you should use buffers definitely. If you have however only neutral (uncharged) molecules, than you don't need any buffer, but than you also don't have to worry about the pH at all.
By Imre Molnar (80-internet-fuer-berlin-bei.online-now.de - 195.211.16.80) on Friday, July 16, 1999 - 04:11 pm:
To the question about precipitation of buffer:
If you work at increasing pH > 4 with K-phosphate, you generate more and more K2HPO4, which is hardly soluble in acetonitrile at room temperature. However there are two tricks:
1. use instead K rather Na-H2-phosphate salts
2. work at 60-70°C, the solubility of your buffer salt will increase considerably. You can run your gradient up to 100% acetonitril and nothing will happen.
Your buffer salt should be fresh, at least not too old (no polyphosphates in it).
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