515.4 question

[Bigbear]

I've asked my EPA region rep this question but have gotten no reply.
The step where the sodium sulfate is acidified using ethyl ether as a solvent can MTBE be substituted. I can see no problem with this change, but...
This is our only use for ethyl ether and would prefer to not have it here.

[Yama001]

I just checked with the crew I work with - they do not use a solvent at all. I would be worried about clumping, poor distribution of the acid, etc, but they seem to be happy with it.

[Bigbear]

Thanks, but how do you dry the extracts prior to esterification?

[Yama001]

Oh they are using the acidified sodium sulfate to dry the extract. They are just making the acidified sodium sulfate by mixing a 1:1 sulfuric acid/water with the sodium sulfate and, presumably, mixing it well enough so they do not see thier analytes removed during the drying step. They pass thier QC requirements, but environmental methods have a lot of holes in them.

I believe the procedure recommends ether simply because other steps in the process also calls for ether (under the 8000 series methods anyhow). I would guess MTBE is a sensible choice; however, getting your particular mix of internal state/federal regulators signing off is always a crapshoot.

[montucky1]

Bear,
if you don't notice any loss in sensitivity i would use the mtbe. the substitution is not actually changing the chemistry of the extraction, just the solvent used in preparing a component of the extraction... as long as the NaSO4 is acidic i don't think it matters how it was made... I've been told that changing the chemistry of the extraction is a no-no...

if you haven't gotten an answer yet, hope this helps.