From: "STRAUGHN, John" <JSTRAUGHN**At_Symbol_Here**FPM.WISC.EDU>
Subject: Re: [DCHAS-L] Perchloric acid use
Date: Wed, 8 Jul 2015 21:14:34 +0000
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Message-ID: 1B6A9D383A771846BE7E63C1D8758E2F404C327D**At_Symbol_Here**

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**]On Behalf Of Koster, Sandra
Sent: Wednesday, July 08, 2015 1:58 PM
Subject: [DCHAS-L] Perchloric acid use


I have a researcher who would like to run small-scale (~300 microliter) digestions with perchloric acid but we don't have a perchloric acid hood.  Does anyone know of a trap that we could use in a regular fume hood to prevent vapors escaping to cause a safety hazard? Or perhaps the set-up described below is sufficient to minimize potential problems.   

To quote: "The experiments that we run here and have been trying to bring back to UWL involve a step where we assay for lipid concentration by cleaving the phosphate group using perchloric acid.  The cleavage is done with only 300 uL of perchloric acid per sample, and the samples are capped with a glass marble under reflux conditions (air cooled at the tops of the tubes) so that very little, if any, perchloric acid escapes from the tubes......The problem (I believe) is that the hoods at UWL are not spec'd for use with perchloric acid.  We have been trying to develop an alternative assay, but it is not working and it is using a lot of time and resources.  Is there any way we can use the perchloric acid version at home and move forward with meaningful experiments?."


Sandra Koster, Senior Lecturer

University of Wisconsin-La Crosse



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