Chromatography Forum

Hi all,

Our lab has a lot of soxhlet glassware that gets used regularly. Many of the round bottom flasks have a baked-on brown layer from so many uses. I want to try and clean this residue off. Methylene chloride, hexane, nitric acid, sulfuric acid, nothing touches it. I even tried aqua regia yesterday with no effect. Any suggestions?

If orange terpenes are an option could be worth a try

In the good old days I'd recommend Chromic Acid (Potassium Dichromate in conc sulphuric acid). It will oxidise/remove pretty much anything organic from glassware with a good soak, and you can keep using the acid as long as it stays orange, however it is super corrosive, toxic, carcinogenic and presents problems in disposal so generally not allowed in the modern lab.

1,1,1 Trichloroethane works really well for removing burnt on hydrocarbon deposits.
The caveat of course is that it's pretty hard to get these days and it's really bad for the environment and for humans as well.
Back in the 'good old days' we would use it to wash nearly everything, from dirty ion sources to glassware, but then again we used to use benzene in the lab too. For those who don't know, benzene has a really nice sweet odor. Too bad it's so gosh darn toxic.

Kilning is an option, but it could cause active sites on the glass and if you're doing PAH's or other environmental type extractions it can cause all kinds of mischief.

'Crabs

In the good old days I'd recommend Chromic Acid (Potassium Dichromate in conc sulphuric acid). It will oxidise/remove pretty much anything organic from glassware with a good soak, and you can keep using the acid as long as it stays orange, however it is super corrosive, toxic, carcinogenic and presents problems in disposal so generally not allowed in the modern lab.

There is a replacement called NoChromix, which is mixed with conc sulfuric acid and does the same thing without the chrome so much easier on disposal.

Muffle furnace at 400-450C will also burn off most organic contamination, I use that to clean injection port liners all the time. If worried about active sites you can silanize the glass with some SylonCT.

There is a mixture of sulphuric acid and hydrogen peroxide called piranha fluid. It will eat anything organic. https://en.wikipedia.org/wiki/Piranha_solution

I used to get a roasted residue in my microwave digestion vessels when I did organic samples. Alconox or Hexane did nothing but Acetone strips it right out. Acetone or Acetone/Hexane also cleans up my soxlet flasks really well. All soxlet samples I get are soils for oil and grease. I also used to clean up my sand blanks for DRO by soxlet extracting the sand with 50:50 Acetone/Hexane. They are nearly inseperable by distillation but easily separated with water.

...
Muffle furnace at 400-450C will also burn off most organic contamination, I use that to clean injection port liners all the time. If worried about active sites you can silanize the glass with some SylonCT.

Based on your experience, is it OK to heat volumetric flasks etc to 500 °C?
Best regards
Jörg

...
Muffle furnace at 400-450C will also burn off most organic contamination, I use that to clean injection port liners all the time. If worried about active sites you can silanize the glass with some SylonCT.

Based on your experience, is it OK to heat volumetric flasks etc to 500 °C?
Best regards
Jörg

Probably not if you want them to remain volumetrically accurate. I went to work for a lab that had baked their volumetrics that way and many of them had sagged because they far exceeded 500C. Fortunately I was doing metals not organics and had my own volumetric glassware.

From this link...
https://stason.org/TULARC/science-engin ... index.html

"16.2 What is the effect of oven drying on volumetric glassware? (Chemistry)

Many older laboratory texts insist that volumetric glassware should not
be oven dried because of the danger of irreversible and unpredictable
volume changes. However most modern laboratory glassware is now made of
Pyrex, and work by D.R.Burfield has demonstrated that low temperature
drying does not significantly affect the calibration of volumetric
glassware [10]. He demonstrated that exposing volumetric flasks and
pipettes to 320C, either continuously or thermally cycled, resulted in no
significant detectable change to the calibration. He concluded that
"oven temperatures in the range of 110-150C should provide efficient drying
of glassware with no risk of discernible volume changes, even after
prolonged use, providing that Pyrex glass is the material of construction". "

Have you tried the dilute EDTA solution people clean coffee pots with?

I want to try piranha solution but a little nervous to make it. I have the hydrogen peroxide and sulfuric acid ready, just haven't had the time to try it out yet.

I have not heard of EDTA but will look into it.

Thank you.