Chromatography Forum

Hello all,

can anyone tell me what is "bonded" and "nonbonded" in column phase ?

Thank you

Bonded is when the phase is chemically bonded to the inside of the fused silica capillary, a more modern version of early non-bonded columns. Most columns these days are bonded, except for some very polar phases. Bonded phases can actually be cleaned by reverse-flushing with organic solvent; there are kits for this, and I've had success doing this.

There was a lot of debate when so-called bonded columns first came out as to whether the phase was chemically attached to the fused silica surface. However, it seems much more likely that the stationary phase is merely crosslinked, which helps to confer solvent resistance on it. This is done by adding eg free radical initiators to the stationary phase such as organic peroxides-however, other methods have been used, even I think irradiating the column. Therefore, it may be possible to rinse these columns off-line with organic solvent to clean them, although I don't know how many people actually do this- but CPG seems to have had some success. A more important advantage of such phases may be in their increased solvent resistance during GC injection in techniques where condensed solvent is in contact with the phase e.g cold on-column injection, or splitless injection using the solvent effect. In non-bonded phases, some dissolution and redeposition of phase at the front of the column can sometimes occur in these techniques, causing loss of performance.