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UCT offers both endcapped and unendcapped C18, in 10 g, 100 g, and 1 kg packings:Does anyone know where to buy quantities of bulk C18 ODS (in powder form, not already packed in SPE cartridges)?
UCT offers both endcapped and unendcapped C18, in 10 g, 100 g, and 1 kg packings:Does anyone know where to buy quantities of bulk C18 ODS (in powder form, not already packed in SPE cartridges)?
http://unitedchem.com/products/Sample+P ... asorb.aspx
Unendcapped C18 is useful if you are trying to retain moderately polar to non polar compounds. Hydrogen bonding occurs between the unreacted silanol groups and the hydroxide functionality on the analyte.
Endcapped C18 is preferred for non polar compounds because it does not retain any polar compounds that could be in the matrix, thus providing a cleaner extract.
Thanks for clearing that up, Don. Otherwise I was sort of grasping for straws, thinking of select labile analytes being 'degraded by free silanols' and losing a few percent here or there. In my case I'll go mostly with the endcapped...it should still retain slightly polar compounds like monoterpene alcohols and aldehydes and aliphatic alcohols (1-octanol and decanol), as well as more fully non-polar compounds like terpene hydrocarbons and esters.
As long as the LogP of your analyte is greater than 1, endcapped C18 has a good chance of working for you.
Unendcapped C18 is useful if you are trying to retain moderately polar to non polar compounds. Hydrogen bonding occurs between the unreacted silanol groups and the hydroxide functionality on the analyte.
Endcapped C18 is preferred for non polar compounds because it does not retain any polar compounds that could be in the matrix, thus providing a cleaner extract.