Why is it allowable to use the same pipette tip??

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angelyn1985
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Why is it allowable to use the same pipette tip??

Post by angelyn1985 » Tue May 06, 2008 7:35 pm

I wonder why it is allowable to use the same pipette tip for bacterial count on plates if we start with the lowest dilution and then the next lowest dilution??

Cat
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Re: Why is it allowable to use the same pipette tip??

Post by Cat » Tue May 06, 2008 7:38 pm

If you start with the lowest concentration and go to the highest, carryover amount is negligible.

angelyn1985
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Post by angelyn1985 » Tue May 06, 2008 7:39 pm

I see! Thanks!!

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canalon
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Post by canalon » Tue May 06, 2008 7:41 pm

Simply because the amount of bacteria from the diluted sample is negligible compared to the amount in the next tube. With 10 fold dilution, even if you were to plate the totality of the lower dilution there would be less than 10% error. Since it is likely that you will in fact empty closer to 99%of the volume in your tip, that makes an error closer to 0.1%. This is lower than the accuracy of most pipettes. Ergo, save yourself some work, and some tips.
Patrick

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any proof. (Ashley Montague)

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MrMistery
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Post by MrMistery » Tue May 06, 2008 7:53 pm

Lol... This thread reminds me... I once worked with 24 flasks using the same pipette. Talk about saving....
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

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