Reverse phase supports usually have a silica base (chemically polar with acidic and basic character), which is reacted with chemical attachments which give it a non-polar character. Not all of these reactive sites are blocked with a non-polar functional group and some active sites are embedded metal ions in the silica.
A second chemical reaction is often executed, blocking many of these active sites, but different procedures give differing results. This is also affected by the quality of the silica starting material.
The unblocked acidic sites can be temporarily blocked by an amine like TEA which reduces interactions with an analyte with the silica backbone of the RP support. This blocking reduces the interaction of the acidic sites which may remain on the support which cause 'tailing' of the peaks eluting from the column.
Advancements have been achieved with the chemical reactions blocking these active sites so TEA does not improve many of the newer columns performance.
Unfortunately for older columns the TEA is not always completely removed when purged with a mobile phase which is lacking this chemical addition. Performance then for other samples may not reproduce the column's original performance for these samples. This is not a desirable situation.
These factors are why there are so many different RP C-18 columns available. Older columns are still manufactured using their original silica with all of its 'defects' so analytical work produced years ago can be reproduced and some of these columns may require TEA for the testing they were originally chosen to perform.
Make your choice of a column carefully, and after making your choice it behoves you to ascertain that the column will be available in the future and not discontinued.
You should do some reading and there are many books available to teach you the fundamentals of HPLC.
ENJOY !
Rod
