Pipetting

[Maxtor]

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?

[canalon]

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

[blankscreen]

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?

[ZakaSPFC]

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

[blankscreen]

quote ZakaSPFC:

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. 😯

[Navin]

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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[MrMistery]

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

[canalon]

quote MrMistery:

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.

[MrMistery]

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

[firestag]

quote Canalon:

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. 😯

[Poison]

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. )

[MrMistery]

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

[Poison]

Maybe they can let us "touch" them. 😛

[canalon]

Well, you will probably even use some. They are kind of common as soon as you start molecular biology 😉
I got 5 on my bench (different sizes) like everybody else (6 people) plus 1 set for PCR and a few multichannel one.

[Poison]

Wow. How would it feel… 😛
I already used one out of the school but I think we should do more that seeing it. 🙂

[maimutel]

Yeah we had that type of pipete that canalon showed but I remember once I was in lab and a friend of mine accidentally mouth pipeted a reactive that was prepared with H2 SO4 90 % and was interesting to see her tongue losing colour as well as half of her 2 front teeth ….. Takes a genius to put a student to take reactives with the especially knowing how attention can varry once the mobile calls let’s say :p
Her luck was that I had some shampoo to wash my hands in uni so that came as a neutralizer cuz they had no soap around …… wasn’t tasty but the result was imediat ….. she survived :p

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