Chromatography and its principles
The
original language of this article is Chinese and parts of it have been
translated using DeepL
I
would like to share a recent chemistry experiment I did to detect the presence
and reaction of molecules using TLC (Thin Layer Chromatography), a very simple
and useful method that allows you to see the movement and colour change of
molecules on paper with a special piece of paper, some reagents and a UV lamp. I
have used six different colour development methods: UV lamp (254 nm), UV lamp
(365 nm), iodine colour development method, DNPH colour development method,
ninhydrin colour development method, and camelion solution colour development
method.
Each
colour development method has its own characteristics and scope of application,
for example, UV lamp can see green or fluorescent molecules, iodine colour
development method can see brown molecules, ninhydrin colour development method
can see purple molecules, etc. I first cut the paper into small pieces and then
drew ten dots on it with a pencil, and then used a pipette to put different
drops of reagent on the dots. Then I placed the paper under the different
colouring methods and observed the results.
The results
are as follows:
I
have found that each colour development method has its own advantages and
disadvantages, some can see many molecules and some can only see one or two
molecules. For example, the UV lamp (254 nm) can see the largest number of
molecules, eight, while the Camelion solution method can only see one molecule,
the Camelion solution itself. I think this is because different molecules react
differently to different colour development methods, some molecules will absorb
or emit UV light, some molecules will react chemically with iodine or ninhydrin,
and some molecules will not react at all. I also found that some of the colour
development methods affect the results of other colour development methods, for
example, the DNPH colour development method will make the paper yellow, which
will interfere with the observation of the UV lamp (365 nm), because the UV lamp
(365 nm) will also make some molecules yellow. Therefore, I think that when
doing TLC, we should be careful to choose the right method, and also pay
attention to the sequence and time, so that the methods do not interfere with
each other.
I
learnt a lot about molecules through this experiment, such as the polarity of
molecules, the size of molecules, the structure of molecules, the reactions of
molecules and so on. I also learnt about the principles and applications of
different colourimetric methods, such as DNPH for ketones and aldehydes,
Niinhidrion for amino acids and peptides, and Camelion for reducing sugars. |
