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Thread: Correct pipette usage

  1. #1 Correct pipette usage 
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    Hello everyone!

    I have a question about the correct usage of pipettes, in particular, the classical single mark glass pipette. What exactly is it calibrated to? I know it is calibrated to the total dispose of the fluid in it. But there are (at least) 2 ways to do that, as far as I know.

    1) You push the head of the pipette all the way against the glassware you are disposing into into, and release all the holding pressure

    2) You lower the head into the glassware, then releasing the pressure (aka no contact with anything, just the air).

    The 1) option releases slightly more fluid. The 2) is equivalent to the effect of open-air pressure.

    Which one is right?


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  3. #2  
    Bullshit Intolerant PhDemon's Avatar
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    Number (2) the pipettes are calibrated to account for the small amount of liquid that remains in the pipette.


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  4. #3  
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    Indeed I know that they are accounted for the remaining liquid. But both 1) and 2) have some left, so this argument itself was not really enough for me.

    What's more, I've been to 3 diff research facilities this year, all 3 had different opinions about this matter.

    I accept your opinion, but what is your source? Why is 2)'s remaining liquid better than 1)'s?
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  5. #4  
    Bullshit Intolerant PhDemon's Avatar
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    It was how I was taught to use pipettes at university and how I've used them for the last 15 years as a research chemist, it works

    This is off the top of my head (and should be taken as an opinion not fact) but I think using method (2) the remaining amount of liquid in the pipette depends only on air pressure (fluctuations of which, at ground level are of the order of a couple of a percent between very high pressure days and very low pressure days) and so is very reproducible. If the pipette is used in the same way you get the same amount of liquid (within a few percent) left behind. Using method (1), however, there are a lot more variables that will determine the amount of liquid left (angle of contact, surface tension of the transferred liquid, viscosity of the transferred liquid, etc.) which will lead to higher uncertainties in the amount of liquid transferred.
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  6. #5  
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    most pipettes are designed to be what is known as TD, to deliver, just let it flow out naturally, don't blow out whats in the tip
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