Several things could be causing this:
1. Overloading, i.e., too much of the compound in question. Try using a more dilute sample or less volume.
2. Insufficient drying of the applied spot. This can happen with aqueous biological samples, especially concentrated solutions, or hydrophilic compounds like sugars or peptides.
3. Improper choice of adsorbent material or solvent system.
4. Presence of salts.
5. Ionically charged compounds, such as carboxylic acids, amines, etc., at the wrong pH for good resolution on the adsorbent used.
It would be helpful to know what compounds, adsorbent, and solvent system you are using.
Several things could be causing this:
1. Overloading, i.e., too much of the compound in question. Try using a more dilute sample or less volume.
2. Insufficient drying of the applied spot. This can happen with aqueous biological samples, especially concentrated solutions, or hydrophilic compounds like sugars or peptides.
3. Improper choice of adsorbent material or solvent system.
4. Presence of salts.
5. Ionically charged compounds, such as carboxylic acids, amines, etc., at the wrong pH for good resolution on the adsorbent used.
It would be helpful to know what compounds, adsorbent, and solvent system you are using.
Hi Rabi,
I would add more basicely that in Si TLCs, the head will be probably lipids and the tail can be polar polymers such as tannins with plant extracts (it depends on what you are analysing).
Best Regards,
Paul
To expand on Dr. Cotes answers a little regarding pH, a pH modifier may be needed for the sample. Depending on the pH of the silica and the solvent system, a compound could equilibrate between an ionized form and an un-ionized form. For example, an alkaloid may convert between the free base and its conjugate acid. The un-ionized form is less polar and elutes earlier on silica gel (later on C18). Depending on the stability of the two forms, one can see fronting, tailing, or even two apparently well resolved spots. The modifier shifts the equilibration to one form or another. and sharpens the spot. Common modifiers include triethyl amine, and ammonia (more common for dichloromethane/methanol solvent systems).
- Badges
- Science method