Hi,
I am to separate mixture of compounds using 40 gram Reverse Phase (RP) C-18 column. The solvent system is isocratic mix of ACN and Water (10:90).My sample mix. is not soluble in mobile phase. My sample mixture readily dissolves in acetone.
Can i dry load my sample onto normal phase silica and use or should i use only C-18 silica for sample loading
Thanks in advance
You can dry load your sample in a small amount of C18 silica. Nonetheless, your sample should have at least some affinity towards the mobile phase otherwise it will not run down the column.
You can dry load your sample in a small amount of C18 silica. Nonetheless, your sample should have at least some affinity towards the mobile phase otherwise it will not run down the column.
Please see the application note (link below) where it describes and contrasts the different techniques for loading samples into C18 flash columns:
http://www.teledyneisco.com/Documents/Liquid%20Chromatography/Application%20Notes/RediSep%20Rf%20C18%20Flash%20Column%20Loading%20Techniques%20App%20Note.pdf#search=loading
You may use silica since the solvents typically used for C18 are "strong solvents" for silica. This means they cause the compound to elute from the silica. Although water is a strong solvent for silica, it is a weak solvent for C18 I like to use Celite 545 in place of silica since compounds tend to adsorb less strongly to Celite 545. This sort of solid load works best with small molecules.
What sort of compounds are you purifying? My experience is some larger compounds, such as peptides, tend to show poor peak shape when desorbing from a solid load. DMSO or DMF can be used to dissolve such samples, but they can cause the compound to run down the column with little separation between peaks. The trick is to minimize the volume of these sort of solvents.
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