Question

Briefly explain the possible effect of the following experimental errors. TLC plate procedure with drug concentration. 1. You used a 1:200 ratio of ethyl acetate/acetic acid rather than 200:1: (Note: ethyl acetate is significantly less polar than acetic acid) 
2. You allowed the TLC plate to develop too long (past the point where the solvent reaches the top of the plate). 3. You used a plastic pipet rather than a thin glass spotter. 4. You labeled your plate using a pen rather than a pencil:

Answer 1

1. If one has to use 1:200 ratio of ethyl acetate: acetic acid that means the molecule under examination is highly polar. Therefore, if you reverse the polarity (200:1 ration of ethyl acetate: acetic acid) then your molecule will not move due to very non-polar solvent mixture. In such case you won’t get any TLC pattern.
2. If someone allowed TLC to develop to long above top of the plate, then your less polar molecules will reach at top and even some of the non-polar molecules will also cross there Rf value and merge with less polar one. Ultimately, you will end up with wrong judgement and separation of TLC.
3. Generally, glass spotter helps to apply a fine spot on TLC, since organic solvent-glass surface tension is higher. On the other hand, organic solvent-plastic surface tension is very less. Therefore, we you can’t apply fine spot on TLC. The spot will spread and a blurred TLC pattern will be resulted.
4. Generally, ink has organic chemicals/ molecules which shows their own pattern/ merge with molecules under examination due to their solubility in organic solvents. Hence, your TLC plate will be blurred and wasted with ink pen. Rather if you use pencil, which has lead, it won’t be soluble in organic solvent and will not interfere in TLC plot.