I take it that the 300ul of perchloric is as 60 or 70% aqueous and certainly not the exciting 100% variety. Is that acid further diluted in making the process sample? It also seems that this is only a strong acid hydrolysis and not in the true digestion sense, a total destruction requiring heating to dryness. Incidentally, if it's a convincing acid that this needs, trifluoromethanesulfonic acid, triflic acid, should work as well.

The perchloric acid use hood is more for exhaustive digestions where perchlorate is volatilized in the steam from the very forcing reaction and there is frequent use, with lots of large samples. The caution now seems to be over the possibility that metal perchlorate salts build up in places that will detonate if shocked in the case of the hood ducting being demolished for replacement. I don't think that it is really the problem so much as the overall corrosion that could occur with any strong acid used in a similar process; the sulfur trioxide that is boiled off in the Kjeldahl digestion for ammonia nitrogen in protein samples, or such.

The perchloric acid deposition problems in duct work that have led to detonations in demolition are when the duct is constructed with wood and lined with metal or glued-in tiles. Perchloro cellulose is known to be explosive or at least very flammable. The case mentioned in Bretherick's Handbook of Reactive Hazards (under perchloric acid) and in NFPA 491 was with a wood constructed hood with grouted-in tiles covering the wood. Digestions for geological analysis used hydrofluoric acid and perchloric acid, and were of the boil-off type. The HF vapor corroded the silica based grouting and the perchloric acid combined with the glue and wood below. Hazardous excitement ensued when the old structure was hammered in demolition.

Sorry if you are stuck having to obey a rule that really isn't applying in this case; we have occasional calls from labs worrying about perchloric acid solution used at ambient temperature. I think that you can do this as indicated in your question.

From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**med.cornell.edu]On Behalf Of Koster, Sandra
Sent: Wednesday, July 08, 2015 1:58 PM
To: DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU
Subject: [DCHAS-L] Perchloric acid use