Cleaning Cell Culture Tubes

Q: I am using reusable cell culture tubes for boiling urine samples at 121°C with 8M NaOH solution. After this application, there is a white stain inside, which I can’t scrub off.  I used Alconox at the concentration on the container: 3-5 Tbsp/gal. I’ve soaked them, scrubbed them, and then also sonicated in a cold Alconox solution for 30 min. When that didn’t work, I tried applying Citranox. Still no luck.

I considered that there is etching, but if I do repeated cleaning, the stain slowly fades and when wet it looks visibly crystalline. If you have any ideas, I would appreciate your help!

A: Great question and thanks for all the background info.  It is extremely valuable.  

There are three possible types of residues you can be facing with your reusable cell culture tubes. There may be metal oxides/hydroxide precipitates in the urine, or salting out of urea crystals. However, Citranox® Liquid Acid Cleaner should make short work of either. The third thought is that there maybe also be hydrolyzed protein and polypeptide residues in play, where Citranox detergent would not be nearly as effective.

To start, try Citranox soaking/scrubbing/sonication with increased time, temperature and concentration. Try a 4% solution (10 Tbsp/gal or 40 mL/L) for a bit longer at an elevated temp. If this does not do the trick, we recommend trying Tergazyme® Enzyme-Active Powdered Detergent to address any protein or polypeptide residues. The proteases should help immensely over the Citranox cleaner if this is indeed what is happening.

When you use Tergazyme detergent, since it is enzymatic, it is important that the temperature not to be too hot (< 130°F/55ºC) in order to avoid denaturing the enzymes. It’s also important to use a freshly made solution, within 8 hours, to avoid autocatalysis.  (Enzymes are protein too.)  I would begin with a 2-3% (2.5 – 3.75 oz/gal or 20-30 g/L)

If you find Tergazyme detergent entirely effective, you could use it as a single step. If needed, you could also do a two-step enzymatic alkaline followed acidic wash process.  

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