This looks very different to what you presented first, especially "F11-1" doesn't fit any description yet.

Furthermore I have to express great doubt, that the desired output is really clever.

> showing 2 blocks only (the actual file has 61).

61 blocks and 9 solvents, means you will have many cases where the same "solvent" is chosen.

Hence your projected hash-keys <solvent>_<F...> will be overwritten each time you have such a collision. (hash keys are unique!!!)

Do you really want the data of max 9 last different solvents only?

I'd say what you really need is an AoH = array of hashes

@res = (
    {
      solvent => 'h2o',
      F001    => 1.2,
      F101    => 3.2,
      ...
    },
    {
      solvent => 'acetonitrile',
      F001    => 2.2,
      F101    => 7.2,
      ...
    },
    ...
);
[download]

And of course you have to be sure that there is only one solvent = 0 in each block, otherwise ...

edit

or a HoAoH hash of arrays of hashes

$res{'h20'}[0]{F001}= 2.2;
...
[download]