TLC solvents-Calculation

[ssankella]

Hello everyone

I am new to TLC. I am trying to separate fatty acids from phospholipids using this technique.

The digested phospholipids were separated by TLC in chloroform/methanol/ammonia/water (70:30:4:2, vol/vol/vol/vol) and spots corresponding to released free fatty acids and lysophospholipids were removed by scraping and directly transmethylated.

[Stepwise engineering to produce high yields of very long-chain polyunsaturated fatty acids in plants. Guohai Wu, Martin Truksa, Nagamani Datla, Patricia Vrinten, Joerg Bauer, Thorsten Zank, Petra Cirpus, Ernst Heinz & Xiao Qiu]

My question is why does the solvent system make up to a total of 106 instead of a 100???
I cant figure out how to calculate the % of each solvent in the solvent mixture.
Any suggestions are welcome.

Regards
Sankella

[JGK]

Probably because someone started out with a batch of chloroform/methanol(70:30 vol/vol) and rather than repreparing new solutions added some ammonia and water to get the optimum separation.

It's written like that as (probably) thats how the final mix was made plus all numbers are integers and it looks better (neater) than

chloroform/methanol/ammonia/water (66.0:28.3:3.8:1.9, vol/vol/vol/vol)

You calculate the % in the mix by using 106 as the divisor so for chloroform it's

(70/106)*100 = 66.0

[ssankella]

Thank you so much JGK.
That helps a lot.

Regards
Sankella

[Bruce Hamilton]

More likely to keep the formulation in whole numbers with no decimals. It's still quite common in TLC to use whole numbers that total over 100.

As JGK notes, for old style 5 X 20 to 20 x 20cm preparative TLC plates in glass tanks, they often started with one hundred ml of a simple solvent and added 1 - 2 ml of acid, base, or cosolvents via volumetric pipettes for each new trial until they had a method that worked.

[HW Mueller]

Why should the total volume be 100??