DCHAS-L Archives May 18 2011 - Re: Piranha solution

Hi Amy, We commonly used Piranha solution while I was a graduate student at Texas A&M and we were taught to add the peroxide to the acid (though it does seem counter-intuitive to given that you normally add acid to water). You do have to be very careful about adding the peroxide very slowly and you certainly want to make the solution in a fume hood with the sash down (if you can use the solution in the fume hood as well even better). We would use an approximately 1:1 mixture (though we tended to actually use less peroxide than sulfuric acid). Once the mixture has settled down we'd poor it into the frit we were trying to clean and immediately pull it through using vacuum (aspirator attached t o a sink). We would then thoroughly rinse with water. This procedure worked very well for most cases. For others we would clean the frit with aqua regia (by gravity filtration). We only used Piranha solution on frits, normal glassware we cleaned with a base bath (KOH and 70% isopropanol) followed by dilute acid bath (HCl) or if the glassware was delicate we woul d use a no-cromex acid bath. When usingthoroughly as possible BEFORE adding the piranha solution as the solution tends to react vigorously with many organics (another reason to perform the cleaning in a hood). In fact, Piranha solution tends to react vigorously in general, but organics are particularly bad (at least in my experience). As for your other questions, on those rare times we had to refresh the mixture, we would add aliquots of the peroxide. Though as I mentioned abov e we didn't tend the let the solution sit around so this was generally not necessary. I'm not certain why you had a particularly violent reaction with the ferric chloride, but as I said above piranha solution tends to react vigorously in general. We would typically only use nitrile gloves, but they really don't offer muc h protection. If you spilled the solution you had to get the gloves off IMMEDIATELY. I never saw the gloves dissolve, but the heat of the solution was pretty intense. (Piranha solution will burn paper). Heavier gloves, like neoprene, are probably not a bad idea (along with eye protection and a heavy lab coat, piranha solution will destroy clothing. We would use normal glassware when using the piranha solution, it's not corrosive toward glass. That's how we did it in the research group I was a student in at Texas A&M (as taught by my adviser). We never had any major incidents and the glassware got cleaned. Let me know if you have any questions. Edward Funck On Tue, May 17, 2011 at 3:20 PM, Johnson, Amy Carr wrote: > I have been reading about how to make Piranha solution and I keep coming > across this statement, =93Add the acid to the peroxide, although some > authorities disagree=94 Why would authorities not agree that adding aci d to > water instead of water to acid is best? > > > > I have seen some say add acid to peroxide for initial solution, but *when > refreshing*, add aliquots of hydrogen peroxide to Piranha mixture. Is > that ok? > > > > We recently had an incident when Piranha came in contact with ferric > chloride and instantly reacted > > violently Was this due to the metal, the fact that both are oxidizers, > both, or something else? > > > > I have read that neoprene gloves should always be worn. True? > > > > What type of glass is appropriate for containment? > > > > > --bcaec5489ff725a96404a38d3d07

Once the mixture has settled down we'd poor it into the frit we wer e trying to clean and immediately pull it through using vacuum (aspirator a ttached to a sink).=A0 We would then thoroughly rinse with water.=A0 This p rocedure worked very well for most cases.=A0 For others we would clean the frit with aqua regia (by gravity filtration).=A0 We only used Piranha solut ion on frits, normal glassware we cleaned with a base bath (KOH and 70% iso propanol) followed by dilute acid bath (HCl) or if the glassware was delica te we would use a no-cromex acid bath.

When usingthoroughly as possible BEFORE adding the piranha solution as the solution tends to react vigorously with many organics (another reason t o perform the cleaning in a hood).=A0 In fact, Piranha solution tends to re act vigorously in general, but organics are particularly bad (at least in m y experience).

As for your other questions, on those rare times we had to refresh the mixture, we would add aliquots of the peroxide.=A0 Though as I mentioned ab ove we didn't tend the let the solution sit around so this was generall y not necessary.

I'm not certain why you had a particularly violent reaction with th e ferric chloride, but as I said above piranha solution tends to react vigo rously in general.

We would typically only use nitrile gloves, but t hey really don't offer much protection.=A0 If you spilled the solution you had to get the gloves off IMMEDIATELY.=A0 I never saw the gloves dissol ve, but the heat of the solution was pretty intense. (Piranha solution will burn paper).=A0 Heavier gloves, like neoprene, are probably not a bad idea (along with eye protection and a heavy lab coat, piranha solution will des troy clothing.

We would use normal glassware when using the piranha solution, it's not corrosive toward glass.

That's how we did it in the researc h group I was a student in at Texas A&M (as taught by my adviser).=A0 W e never had any major incidents and the glassware got cleaned.

On Tue, May 17, 2011 at 3:20 PM, Johnson, Amy Carr <amy_johnson**At_Symbol_Here** harvard.edu> wrote:

I have been r eading about how to make Piranha solution and I keep coming across this sta tement,=A0 =93Add the acid to the peroxide, although some authorities disag ree=94=A0=A0 Why would authorities not agree that adding acid to water inst ead of water to acid is best?

=A0
I have seen some say a dd acid to peroxide for initial solution, but when refreshing, add a liquots of hydrogen peroxide to Piranha mixture.=A0 Is that ok?
=A0
We recently had an incident when Piranha came in contact with ferric chloride and instantly reacted
violently Was this due to the metal, the fact that both are oxidizer s, both, or something else?

=A0
I have read that neopr ene gloves should always be worn.=A0 True?
=A0
What type of glass is appropriate for containment?< /p>
=A0
=A0

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