We are having a bit of a debate on weather or not the glass stoppers for our volumetric flasks should be greased.
We find sometimes the stoppers on our larger flasks to be dry-locked sometimes so it will be difficult to dislodge the stopper. Chances are that the stoppers were put onto empty flasks or else have been sitting in a flask for days.
We mainly measure fatty acids and vitamins in biologicals. We also use organics such as chloroform, hexane, methanol and also water inside the volumetric flask.
Many times the liquid is poured out of the volumetric flask once the solution is made.
Would there be contamination issues with greasing the stoppers? What is the correct laboratory procedure when it comes to using volumetric flasks and glass stoppers?
A minimum amount of high quality grease is alowed for flasks used for storage, depending on the nature of the liquid containing. With water as solvent there should be no problem.
For an exact volume, when preparing a standard solution in a volumetric flask, grease should be avoided since it may effect the meniscus.
Have you considered using plastic stoppers on your flasks?
See also https://jaytecglass.co.uk/volumetric-flask-instructions-for-use/
Hello Jos,
Thanks for the answer. We have thought of using plastic stoppers however, we also use organics such as chloroform which do not readily enjoy plastics.
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