Why would a basic compound tail more on my new reverse-phase column and then tail less as I make more injections? - WKB235916
Article number: 235916
ENVIRONMENT
- Reverse-phase column
- Tailing
- Peak shape
- Silanol
ANSWER
Tailing of basic analytes occurs as follows:
- Surface silanol groups (Si-O-) on the particle surfaces are generally negatively charged in a pH greater than ~2.0.
- Bases are generally positively charged in a low pH environment.
- Tailing occurs because positively charged bases ion-pair with negatively charged silanol groups on the particle surfaces.
When a reverse-phase, silica-based particle column or hybrid particle column is new and your method is in a pH >2.0:
- The surface silanols become negatively charged, so the column acts as both a reverse-phase column and a cation exchange column.
- As injections are first made, the basic analytes have full access to ion-pair with these silanol groups.
As more injections of a basic analyte are made onto the column:
- Basic analytes from previous injections may adsorb to the packing by ion-pairing to the silanol groups.
- As more analyte ion-pairs to the packing, there are fewer and fewer silanol groups available to attract basic analyte from subsequent injections.
- As a result of less access to silanols, later injections might show less tailing. This process of "blocking" analyte-silanol interaction is called "conditioning".
ADDITIONAL INFORMATION
One way to lower the amount of tailing on a new column on which this trend has been observed is to make at least three "conditioning injections" onto the new column with a high concentration standard of a basic analyte. The goal of this step is to saturate active sites (silanol groups) with basic analyte to block analyte-silanol interactions in future sample injections.
Also see:
id235916, UPBINARY