Why is ammonium bicarbonate the recommended high-pH buffer instead of ammonium carbonate? - WKB251238

ENVIRONMENT

• Buffer selection
• Ammonium bicarbonate
• Mobile phase
• High pH
• Hybrid particle
• BEH reverse phase 
• BEH Amide HILIC 
• Atlantis BEH C18 AX
• Column care and use

ANSWER

The recommendation to use ammonium bicarbonate buffer instead of ammonium carbonate buffer at high pH is due to the following concerns:

1) Ammonium carbonate in water converts/breaks down to ammonium carbamate and ammonium bicarbonate. As the ammonium carbonate concentration increases, there can be formation of an intermediate reactive urea (more ammonium carbamate). The ammonium carbamate and urea will build up in the mobile phase in presence of water. In addition, the ammonia from the buffer will interact with carbonic acid in the water (which is the reaction of CO₂ and water) to form more urea. Urea can continue to build up in the mobile phase and, in concert with increasing levels of ammonium carbamate, will attack the protective oxide layer on the surface of steel and further expose the steel to corrosion. 

2) Carbonate and phosphate buffers at high pH will increase the rate of silica dissolution in the columns as the column temperatures increase. This is slower with the hybrid particles than with the 100% silica particles.

ADDITIONAL INFORMATION

For additional column resources, see WAT038216 - HPLC COL THEORY TECH/PRACTICE  BOOK, by Uwe D. Neue and John Dolan,

LC-GC article: https://www.chromatographyonline.com...hemical-attack,

and journal article: G. Tindall, R.L.Perry (Feb 2003) "Explanation for the enhanced dissolution of silica column packing in high pH phosphate and carbonate buffers", Journal of Chromatography. A Vol 988 Issue 2; 309-312