Sciencemadness Discussion Board

Piranha solution

WeaponsRx - 14-2-2015 at 03:12

I need a very sufficient way of cleaning my Büchner funnels PTFE filter holder which of course piranha juice is the most effective but highly explosive lol.... So Id rather pass on that juice and hear any suggestions you guys may have? A good cleaner before placing into the autoclave... Thanks guys!

BromicAcid - 14-2-2015 at 05:42

Perhaps Piranha Solution Alternative would have been a better title for this thread. Princeton University has a good no-nonsense guide for piranha here:

http://web.princeton.edu/sites/ehs/labsafetymanual/cheminfo/...

Proper precautions taken, i.e., a dry filter so no extra solvent around and no gross organic contamination, the risk of explosion can be significantly mitigated.

The old-standby of dichromate/sulfuric acid, while not known for being as temperamental, does pose long-term health issues (and potential metal contamination of the filter). I have also used KOH/EtOH which does have the advantage for you that you don't have to worry about it eating your filter. Additionally. I have soaked them in concentrated ammonia solution for some stubborn stains. Concentrated nitric is also an option.

Chemosynthesis - 14-2-2015 at 05:53

I agree with all of the above BromicAcid has said. For some stubborn stuff, I have generally used a base bath of sodium hydroxide in water overnight, except for jointed glassware, fritted funnels, or if glassware was to be left over a weekend, both of which meant a fuming nitric bath.

Pouring acid into the inverted funnel (in an appropriate container) and leaving generally works well if your funnel is clogged.

smaerd - 14-2-2015 at 07:25

I have yet to see pirhana solution become explosive. I don't use it at home of course. Sure if you add a lot of pirhana to a bunch of solvent well bad things are going to happen. If you have some organic grime though, it'll chew it up fine.

Bromic using dichromate at home is basically asking for some toxic waste.

Chemosynthesis, I also have had good success with fuming nitric acid. I would use 10-20 mL, and let it fizzle away inside of a sealed flask for a day or so. Shake it around, then add it to another flask etc, Then nuetralize it. So small volumes, and it kept my slightly gunky flasks and filters from being real bad over time. That stuff ripped up a flask that was tainted with a coordination compound, was wonderful.

It really depends on what you're cleaning from your buchners. I usually just spray acetone and water through mine. Maybe spray isn't the right word. I use them for small quantities of organics. For inorganic compounds nitric, or even vinegar soaking might work depending on what the compounds are.

Does PTFE handle well in autoclaves?

Dr.Bob - 14-2-2015 at 19:18

You don't want to soak PTFE in a base bath, it can be etched badly by strong base over time. Acid is better, Nochromix is a safer version of the old chromate bath, not sure what is in it, but not hard to find out.

DrMario - 15-2-2015 at 03:55

We use Piranha at 120C every day in my research institute, for cleaning stubborn organic contamination of all kind, from our glassware. Of all the etchants commonly in use in our labs, Piranha is the one most effective at scorching your flesh, so it commands a hefty dose of respect, but explosion is NOT the main reason to fear it.

Piranha is definitely a force that can be tamed, but do wear protective equipment, including full-face protection, long thick gloves and a tyvek apron. Also, have a water shower on the ready.

WeaponsRx - 16-3-2015 at 19:18

Quote: Originally posted by Dr.Bob  
You don't want to soak PTFE in a base bath, it can be etched badly by strong base over time. Acid is better, Nochromix is a safer version of the old chromate bath, not sure what is in it, but not hard to find out.


So you recommend Nochromix as an over all good solution for cleaning my buchner and glassware? It only sees organics, and organic solvents, BA, BB, Guiacol... PEG's... polysorbate, thats all really... oh and methanol on occasions... but besides those usually everything else is just organics..

[Edited on 17-3-2015 by WeaponsRx]

HgDinis25 - 4-4-2015 at 13:02

Every source I find that gives a procedure for the preparation of Piranha Solution states that the Hydrogen Peroxide must always be added to the Sulfuric Acid, never vice-versa. This is because, they explain, the concentration of Hydrogen Peroxide, if too high, may cause an explosion.

If we have Sulfuric Acid and we add to it Hydrogen Peroxide (for more clarity, let's say add Hydrogen Peroxide dropwise) wouldn't we be increasing the concentration of the Hydrogen Peroxide? Sulfuric Acid would be absorbing the water from each drop, heating up, even forming highly dangerous Hydrogen Peroxide gas?

However, if we added the Sulfuric Acid to the Hydrogen Peroxide none of this would happen. Yes, the solution would heat up a lot. But there would be a lot of water to be taken by the Sulfuric Acid. Thus, the concentration of Hydrogen Peroxide wouldn't increase as much.

If one must maintain a low concentration of Hydrogen Peroxide, the right thing to do wouldn't be adding the Sulfuric Acid to the Hydrogen Peroxide?

stoichiometric_steve - 4-4-2015 at 13:35

On a side note, i once soaked a fritted glass filter in about 50ml of Piranha acid in a glass beaker for a week, the beaker sat in a larger steel pot.

Somehow the Piranha acid managed to crack the beaker and ate all the way through 8mm of the pots' steel bottom. I assume the beaker might have had a defect in the glass to begin with.

aga - 4-4-2015 at 13:51

My personal experience is that H2SO4 + H2O2 (3%) works very well for cleaning just about every nasty sticky nonsense that ever stuck, and neither the glass nor i ever got blown to smithereens.