The reactions required for genetic analysis at the mlecular level require VERY
small amounts of DNA, reagents, and enzymes. The two most common units of
liquid measurement that are used in these laboratory experiments are the
milliliter (mL) and the microliter (uL).
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1 mL = 1/1,000 liter
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1,000 mL = 1 liter
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1 uL = 1/1,000,000 liter
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1,000,000 uL = 1 liter
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Use of Micropipets:
Digital micropipet
| There are three important DON'TS when using a digital micropipet: |
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(1)
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DON'T attempt to use the pipet without a tip in place. This can ruin the
precision piston that determines the volume of the fluid.
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(2)
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DON'T lay down a pipet that has a filled tip. Fluid in the tip could
run back into the pipet and ruin the precision piston.
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(3)
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DON'T let the delivery button (control button) snap back after
withdrawing or delivering the fluid.
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To use a digital pipet:
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(1)
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Rotate the delivery button to the desired volume.
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(2)
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Push the pipet, firmly, into the proper size micropipet tip.
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(3)
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While withdrawing or expelling liquid, hold the vessel and pipet at
nearly eye level. It is important to watch while you pipet.
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(4)
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Hold the pipet close to the vertical while pipeting.
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To withdraw a sample:
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(1)
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Depress the button to the first stop and hold the button in that
position. Dip the tip of the pipet into the fluid to be pipeted and slowly
release the button to draw the fluid into the tip.
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(2)
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Slide the tip of the pipet along the side wall of the reagent tube to knock
off excess fluid that might have remained on the outside of the tip.
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To expel a sample into a reagent tube:
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(1)
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Touch the pipet tip to the in side wall of the reaction tube (microfuge
tube) into which the sample will go. This will help create a capillary effect
which should help draw the fluid out of the pipet tip.
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(2)
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To expel the sample, slowly depress the button to the first stop. Wait a
second or two and then press on to the second stop to blow out the last bit
of fluid.
Continue to hold the button in the second position as the pipet tip is
withdrawn from the tube.
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(3)
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To eject the tip (if the pipet has this feature), press the ejector
button down while the pipet is held over a beaker which has been designated
as the proper receptacle for used tips.
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To prevent contamination of the reagents used in the
laboratory, follow these guidelines:
- Always add appropriate amounts of a single reagent sequentially to all reaction (microcentrifuge) tubes.
- Release each reagent drop onto a NEW LOCATION on the inside wall of the reaction tube. In this way you can continue to use the same tip to pipet a number of samples of a single reagent into different reaction tubes.
- Use a fresh pipet tip for each new reagent you pipet.
Microcapillary pipet
Capillary micropipets are capillary tubes that are marked to accept a specific
microquantity of fluid. Usually they employ a bulb-type plunger, or a thin
metal rod for suction. If due care is used, they are an accurate and economical
way to apply samples for use in electrophoresis.
(Bulb Type)
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(1)
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Insert the pipet through the hole pierced in the amber rubber cap.
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(2)
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Hold the black rubber bulb between the thumb and third finger.
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(3)
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Fill pipet by capillary attraction.
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(4)
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To expel place index finger over the hole in the black rubber bulb and
squeeze.
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(Piston Type)
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(1)
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Insert the metal piston (wire) all the way into the capillary tube.
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(2)
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Dip the tip of the capillary tube into the fluid, pulling back on the
wire piston to fill tube. Draw up to the line.
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(3)
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To expel, push down on the wire piston.
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To prevent contamination of the reagents used in the
laboratory, follow these guidelines:
- Always add appropriate amounts of a single reagent sequentially to all reaction (microcentrifuge) tubes.
- Release each reagent drop onto a NEW LOCATION on the inside wall of the reaction tube. In this way you can continue to use the same tip to pipet a number of samples of a single reagent into different reaction tubes.
- Use a fresh pipet tip for each new reagent you pipet.
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