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Pipetting

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Pipetting

Postby Maxtor » Sun Jan 15, 2006 8:51 pm

1) Why is it necessary to wait a 3-10 seconds after I have initially dispensed the solution from the pipet, before blowing out the rest of the solution?

2) Do I need to equilibrate the tip for volumes less than 10 microliters?
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Postby canalon » Mon Jan 16, 2006 2:04 am

Looks like question about a lab, but I will give you some hints.
The first one, except maybe for extremly special applications nobody does that in the real life ;) HEy come on, we have to go on the forum rather than wating time on those experiments.

More seriously, for 1 its depends on the viscosity of your liquid, how you empty your pipet etc. The point being that if the solution sticks to the side of the tip it will slowly go down in the time you provide.

for 2 I never do it, but for these volume I think this may rathr increase the risk of errors
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Postby blankscreen » Tue Jan 17, 2006 12:35 am

in my old school, we used glass pipettes and our teacher told us to use our mouths to suck in the chemical into the pipe (kinda like using a drinking straw halfway) and then tranfer the pipette into the beaker/test tube and let go so the chemical would come out. I thought our teacher was crazy and did not do that. Was I right or was she?
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Postby ZakaSPFC » Tue Jan 17, 2006 1:48 am

well if I am interpreting what you are saying right the answer is no. You should not put chemicals in your mouth. Also who knows how well she washed those things
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Postby blankscreen » Tue Jan 17, 2006 2:51 am

ZakaSPFC wrote: Also who knows how well she washed those things


That's exactly what worried me most. I don't think she used soap at all. And there were like, what? 200 other students using those pipettes? There's no way I was putting those in my mouth. :shock:
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Postby Navin » Tue Jan 17, 2006 9:10 am

In my school we are allowed and also taught to use the pipette by using our mouths. However, you must be very careful not to suck the chemical all the way into your mouth.

The other alternative was to use the special hand pump (pictures shown below)
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Postby MrMistery » Tue Jan 17, 2006 6:40 pm

Well, that pippete is manufactured in such a way tht you need to use your mouth. But i think the person who invented it thought everyone will have his own pippete. And the pippete mentioned by Maxtor is a special pippete, used only for extremely small volumes. 10 microliters=0.2 drops of water in average
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Postby canalon » Tue Jan 17, 2006 7:19 pm

MrMistery wrote:Well, that pippete is manufactured in such a way tht you need to use your mouth. But i think the person who invented it thought everyone will have his own pippete. And the pippete mentioned by Maxtor is a special pippete, used only for extremely small volumes. 10 microliters=0.2 drops of water in average


Well in France even in school mouth pipetting is completely forbidden, so we had to use the kind of contraption pictured above. There are many types, some are good some are just crap. Still I learned to mouth pipette, and considering the washing standard in a lab (you want to avoid chemical contamination when changing pipettes, so the washing has to be very careful) my concern is more what I risk to inhale/drink than who put his/her mouth on it before. And you usually do not reuse the same pipette, you just take a new clean one. More so if you want to work in sterile condition (where disposable are more convenient, and cheaper in the long run).

But to pipette in the order of magnitude desired by maxtor you definitely cannot use glass pipettes (even if I remember seeing in one of my labs some capillary tubes designed just for that, not the easiest to handle though, and you need one type per volume...). So you just use this kind of thing. And then you can come up with the kind of question our friend maxtor come up with.
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Postby MrMistery » Tue Jan 17, 2006 7:35 pm

Yea, that's it. I only used that kind of think once in my life, when i did a PCR experiment and had to mix some things. I like the use-once tips
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Postby firestag » Tue Jan 17, 2006 7:50 pm

Canalon wrote: I never do it, but for these volume I think this may rathr increase the risk of errors

I never do it either.
I also have never used a pipet that you must suck stuff up.
But i dont think i would use it. :shock:
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Postby Poison » Wed Jan 18, 2006 9:23 pm

It is forbidden for us to use our mouth in the lab too. It is dangerous (depending on the substange you are working with.)
And those automatic pipettes, as Patrick showed, are more safe to use. ( well, we didn't use it at school but i used it in a lab. Those are too expensive to be given to the students. ;) They say we will "see" them in our 3rd year. )
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Postby MrMistery » Thu Jan 19, 2006 7:43 pm

As in they will take you to where they are kept and show them to you :d
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