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Tuesday, January 23, 2007

Removing wax or petrolatum from glassware

What is the best way to remove wax or petrolatum from pipettes and other glassware?

The best way to clean wax and petrolatum from pipettes and other glassware is to use very hot, emulsifying 1% solutions of cleaners such as Alconox or Liquinox. By very hot, I mean above the melting point, or at least above the softening point of the wax. Typically this can be reached at 170 deg F (77 deg C). In practical terms this is a difficult temperature to reach. It would typically require heating a soak solution on a hot plate or other external source of heat. Petrolatum can be successfully cleaned at as "low" a temperature as hot 140 deg F (60 deg C), although even this is often hotter than you can get out of a hot water tap.

Specifically for pipettes, soak the pipette in the hot or very hot solution of 1% Alconox or Liquinox for at least 10 minutes. Then drain the pipette 3 times filling and emptying with the hot or very hot solution. Then move the pipette to a normal ambient temperature 1% Alconox or Liquinox soak solution to hold it until you are ready to clean in a siphon pipette washer with Alcotabs. You could skip the ambient temperature soak and go directly to the siphon pipette washer with Alcotabs if you want to. The idea is to not let the pipet dry out or be exposed to plain water where trace wax or petrolatum might plate out on the inside of the pipette. With any used pipette whether it has wax and petrolatum residues or any other residue, it is good practice to place the pipette in a 1% Alconox or Liquinox soak solution immediately after use to avoid any residues drying on to the pipette.

If it is not practical to pre-soak in a very hot or even hot 1% solution of Alconox or Liquinox, you can often get satisfactory cleaning from just prompt pre-soaking in an ambient 1% Alconox or Liquinox in accordance with our recommendations for standard pipette handling. Low melting saponifiable natural and synthetic ester waxes can often be adequately cleaned by this method. Higher melting waxes like bees wax, require at least a hot water (circa 140 deg F, 60 deg C) 1% Alconox or Liquinox 10 minute pre-soak. If this is absolutely not practical, it is possible to remove high melting natural and synthetic ester waxes using a 1% Solujet presoak which can saponify the waxes. Note that Solujet is a potassium hydroxide based corrosive liquid that absolutely requires skin and eye protection for use. It is important to immerse the pipette completely in the Solujet solution to avoid etching the glass at the air/solution interface. In fact it is good practice to always completely immerse pipettes or any glassware to minimize any concerns about etching no matter what soak solution you are using (even deionized water). Normally we do not recommend Solujet for manual cleaning operations unless it is absolutely necessary. Petrolatum in heavy quantities in the absence of emulsifiers that may be present in the cream or lotion you are working with may not be adequately cleaned by the simple ambient temperature pre-soak. If the cream or lotion with the petrolatum contains emulsifiers that are effective on petrolatum already, even an ambient temperature pre-soak in 1% Alconox or Liquinox can be effective. Note that Solujet is not particularly any more effective on petrolatum than Alconox or Liquinox.

Alconox, Liquinox, and Solujet are available from leading laboratory supply companies such as VWR, Cole-Parmer and Thomas Scientific.

Technical bulletins and msds for these cleaners are available at the top center of our home page at

We would be happy to provide samples of any of these cleaners on request.

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