I don’t even want to guess how many times you would need to rinse this syringe before removing all traces of reanimation “reagent”…
This How Dirty Are You? blog should really be credited with inspiring the entire project. I was discussing the number of times I rinse my syringes with a colleague, Michelle Misselwitz, a few years ago. We were working in the same hood and I noticed that she rinsed her syringe a lot…I do too. I was even reminded of my rather obsessive rinsing at Thanksgiving this year. I was washing a few dirty dishes by hand and my mother mentioned that I was rinsing them a lot…and that my grandmother would have been upset because I was wasting so much water…but “What about the soap residue?” I said.
Over the years, I have been told different things about the number of times a syringe should be rinsed to prevent carryover/contamination…and I have been asked the same question many times. I was told early in my lab career that 7 was the magic number…so just to be sure, I got in the habit of using 10 rinses.
What We Did
There are a lot of variables to consider…sample matrix, compound concentration, sample solvent, rinse solvent(s), rinse volume etc. But to keep things simple, we used a hydrocarbon standard at a high level and rinsed with the same solvent as the sample solution, acetonitrile. We also defined the volume of a “rinse” as 20 µL. We started the experiment with a 20 µL draw of a 500 ppm hydrocarbon standard. The hydrocarbon standard was expelled and then consecutive rinses were performed. Each rinse was tested by GC-FID.
Sequence of manual syringe rinsing:
1. 20 µL draw of a 500 ppm hydrocarbon standard and expel it
2. 20 µL draw of acetonitrile – eject into sample vial – test via GC-FID
3. Repeat step 2 many times
Question
1. How many 20 µL acetonitrile rinses were needed to show no signal (FID)?
(Hint: The answer is between 1 and 15…I didn’t say it was a good hint.)
I say 5. Although I am in the habit of doing triplicate rinses in three separate solvent vials myself, so 5 seems perilously cavalier.
Hi Robert,
Using more than one solvent rinse vial is a great idea!
When I was in school we were taught 3 rinses. Anything beyond that is OCD.
I usually do 10.
Funny!
I usually do 10 too, as minimum, always with the solvent used with the references and samples solutions.
I would guess 3-5 rinses.
Hi Maria,
Your comment about using the same solvent for rinses as was used for making the solutions is great advice. At the very least, you know that your compounds are soluble in that solvent at that concentration and so the rinsing should be effective as preventing sample carryover.
thank you
Julie
I say 4, but I usually do 10. Used several solvents is a great idea, especially when the sample is a mix with different solubilities.