Agent Lemon is a tek referring to DXM if I'm not mistaken, citric acid may be used for any number of reasons or teks but I think the name Agent Lemon is for DXM extractions.
There are three reasons why not to use grapefruit juice instead of lemon juice:
1. The pH doesn't match, grapefruit juice = 3 – 3.3 while lemon juice = 2.3 though you
could account for that with (use of less) water.
2. Grapefruits contain naringenin and probably other cumarines/flavanones that inhibit
the enzyme that breaks down DXM. It would potentiate the DXM in an unpredictable
way that is simply not good to mix with extractions.
3. Lemons and their juice are so abundant, why bother with something else?
Nahphta fumes? What about them?
You mean you want to use it for some kind of vapor filter?
I thought the agent lemon refers to lemons being used in the extraction itself,
besides nahphta fumes are okay as long as you don't do the extraction in the closet under
the stair or something. If your technique is okay then there shouldnt be much vapor at all.
But evaporation of such a solvent by heating should be done outside for safety. No grape-
fruit will make that safe so forget about that.