I am trying to verify the results of EPA method 26A (http://www.epa.gov/ttnemc01/promgate/m-26a.pdf). The Method claims to be able to separate and quantify a mixed halogen/halide gas stream. Although I believe the chemistry holds true for Cl₂/HCl and Br₂/HBr, I'm not so sure about F₂/HF. Despite the Method not mentioning F₂, it commonly produces data for both HF and F₂. I am dubious that the F₂ results are real and am trying to develop a chemistry argument to support that position, if possible.
In summary, the Method takes a mixed gas stream (F₂/HF) and passes it through a 0.1 N H₂SO₄ solution, then a 0.1 NaOH solution; sodium thiosulfate is later added to the alkaline potion. The theory is that the HF is captured in the acid solution, while the F₂ passes through unreacted. In the alkaline solution, the F₂ reacts to form HF and the hypohalous acid (HOF, I assume). The thiosulfate converts the HOF to another HF. When the acid and alkaline solutions are analyzed for fluoride ion, the quantity is assumed to be the HF and F₂ in the original sample, respectively.
Considering that F₂ is so reactive, I would think that any F₂ in the gas stream would react with the water in the acid solution and that theoretically no F₂ would make it to the alkaline solution. Is this a reasonable assumption?
If any F₂ did get to the alkaline solution, I am not sure that the conditions are favorable for the creation of HOF; F₂ reacting with water to produce HF seems more probable. Unless the acid solution is ignored by the F₂, I don't think that a true separation is taking place and any fluoride detected in the alkaline solution would represent blow through or some other error. Does this seem like a reasonable conclusion?
Thanks in advance for any input!