What is the purpose of notches in chromatography paper?

[misterW]

What is the purpose of the noches a couple centimeters from the pointed end?

And… what is the purpose of the pointed end?

I’ve done chromatography with a rectangular piece of paper with no notches and it seemed to work fine.

So what are the notches and the pointed end for?

[Squink]

IIRC, and it’s been decades, the notches are used in prep scale descending paper chromatography. After applying sample and drying, the top of the paper is placed in a solvent reservoir and chromatography proceeds down the sheet. The notches become important when the solvent front reaches the bottom. With no notches, solvent builds up at the lower edge and drips randomly off the bottom. This chaos can mess up the flow far up into the paper sheet. Regular notches supply nucleation sites for an ordered array of drips. This stabilizes the pattern of solvent flow in the sheet and allows better resolution.

[misterW]

@Squink

IIRC, and it’s been decades, the notches are used in prep scale descending paper chromatography. After applying sample and drying, the top of the paper is placed in a solvent reservoir and chromatography proceeds down the sheet. The notches become important when the solvent front reaches the bottom. With no notches, solvent builds up at the lower edge and drips randomly off the bottom. This chaos can mess up the flow far up into the paper sheet. Regular notches supply nucleation sites for an ordered array of drips. This stabilizes the pattern of solvent flow in the sheet and allows better resolution.

are we talking about the same process? the notches i’m referring to are about 2 cm above the bottom end (pointed end) of the paper strip. the pointed end is placed in the solvent, which moves up the strip. the sample is placed in between the notches (about 2 cm from pointed end). so, in this case, the solvent reaches the notches in the very beginning.

ideas?

[Squink]

@misterW

are we talking about the same process?

Nope. Your setup is the other way around than mine was. I think the answer is still flow control, but I’m not certain how it actually works in your case.

[Praetor]

@misterW

are we talking about the same process? the notches i’m referring to are about 2 cm above the bottom end (pointed end) of the paper strip. the pointed end is placed in the solvent, which moves up the strip. the sample is placed in between the notches (about 2 cm from pointed end). so, in this case, the solvent reaches the notches in the very beginning.

ideas?

While I’ve never seen chromatography paper with notches in it, I’m going to guess that the notches are simply to mark where to put the spot. It’s been a while since I’ve done chromatography, but I’m pretty sure it’s important to get an accurate measure of the ratio between the distance the solvent front traveled and the distance(s) the spot(s) traveled. When I did chromatography, I was taught to draw a line or two in pencil marking where I put the spot so I could measure later.

[misterW]

@Praetor

While I’ve never seen chromatography paper with notches in it, I’m going to guess that the notches are simply to mark where to put the spot. It’s been a while since I’ve done chromatography, but I’m pretty sure it’s important to get an accurate measure of the ratio between the distance the solvent front traveled and the distance(s) the spot(s) traveled. When I did chromatography, I was taught to draw a line or two in pencil marking where I put the spot so I could measure later.

That was a thought that occurred to me as well (to mark the spot), but it seems a bit excessive, doesnt it? to go through the trouble of cutting out notches? why not just draw a line in pencil? and i’ve seen it clearly stated many times that notches should be cut out – is there no useful reason for it?