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How Dirty Are You? Part 2…Pipet Bulbs...The Question

16 Jun 2014

Check out the first How Dirty Are You? blog about Parafilm.  Restek - How Dirty Are You Part 1 Parafilm...Take a Quiz! 

This How Dirty Are You? blog is all about pipet bulbs. Our lab has 14 people and we have at least a few types of pipet bulbs for both borosilicate glass Pasteur pipets or volumetric pipets. I am sure this isn’t surprising to most of you but each person has their favorite type. Our facility only stocks one kind of pipet bulb so we have to order the other types that we like and this makes for some interesting negotiations. Right now, my colleague, Linx is my supplier for my favorite type of pipet bulb…which is the larger light blue one. Preferences for specific bulbs are strong and we have had many conversations about why we like a particular type. For example, Michelle Misselwitz likes the small black bulb because it helps her prevent pulling liquid into the bulb itself.


One of the goals of the original “How Dirty Are You?”’ project was to find contamination sources that are sometimes overlooked so we tested a few bulbs to see what was lurking inside. I tested the bulb that I had been using for some time, my lab mate Jason Thomas’s bulb and a general latex lab bulb with unknown history on how or if it had been used.

What we did

The inside walls and bottom of the bulb was rinsed continually with 400µL of acetonitrile for about 1 minute. Then one microliter of this was tested by GC-MS using generic testing parameters.

The results

Jason’s bulb looked just like the solvent blank! Very clean…My bulb was a different story. As you can see (blue trace), my bulb was filthy. I know some of this might be the different bulb material but Jason also told me that he periodically cleans his bulb with solvent. I think it is safe to say that this was not a practice I had been doing. The latex bulb (yellow trace) was not nearly as dirty as mine but there were some significant peaks.

chromatographic comparison of pipette bulb contamination


bulb on bookshelf
I promptly retired that pipet bulb and placed it on my office bookshelf…I just couldn’t throw it out after so many months of service…and to this day it still sits there.

I think what surprised me the most was the intensity of some of the peaks. Much of my work deals with trace level analysis, ppb level, so I was not accustomed to seeing such high levels. This figure below shows an overlay of chromatograms from my bulb (blue), the latex bulb (yellow) and a 5 ppm hydrocarbon standard (black). In many cases, peaks from my bulb are much larger than this 5 ppm level and even the general lab bulb shows a few peaks higher than the 5ppm level.

pipet overlay

Finally...Here is your question:

One thing I learned from this project is that there are compounds that are just about everywhere and this is the case with the largest peak of the general latex bulb…see starred peak below. So the question is…

A common additive for rubber was found in the latex bulbs. What type of compound was this?

  1. Dye
  2. Antioxidant
  3. UV Stabilizer

 starred latex bulb