Buffers can cause various problems in the lab. Two common problems include surprising rises in HPLC-MS backpressures when starting the instrument after overnight storage and difficulties with MS sensitivity. Warning: do not use incompatible buffers with MS!
Increased instrument backpressure when using ammonium acetate (and ammonium formate) is a common problem found on chromatography forums, especially when the instrument was standing overnight or on the first few runs of each day. High soluble aqueous buffers can cause a great deal of head scratching. They become problematic in practical use, blocking capillaries, pre-columns, and analytical column end frits.
Potassium phosphate, Ammonium phosphate, Ammonium Acetate in Acetonitrile.
The solubility of ammonium acetate in binary mixtures containing above 90% acetonitrile is increasingly limited in solubility, and wholly insoluble in 100% acetonitrile. While 20mM ammonium acetate is the solubility limit at 90% acetonitrile, this limit falls sharply to 10mM ammonium acetate (a popular buffer concentration used with LC-MS applications) at 95% acetonitrile mixtures. Exceeding these solubility limits results in a cloudy liquid due to the fine ammonium acetate precipitate within the solution. This can block capillaries and column frits, causing an increase in system backpressure.
Credit: LCGC NORTH AMERICA VOLUME 22 NUMBER 6 JUNE 2004, Adam P. Schellinger and Peter W. Carr
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