Pipets and Pipetting

Introduction

Pipets are instruments used to transfer fluids from one container to another. They are one of the most frequently-used tools in the biology laboratory. Your laboratory results will depend heavily on the proper function of the pipets and your proper use of them.


Types of Pipets

A variety of pipets are in use, and different situations call for the use of different types of pipets. 5 different types of pipets along with some of their basic characteristics are listed below. An example of each will be on display and your lab instructor will demonstrate each.

Pasteur Pipet

  • Usually made of borosilicate glass.
  • Always disposable.
  • Not calibrated. Used to transfer small bulk volumes of fluid quickly and inexpensively.
  • Used with a rubber bulb.

Serological Pipet

  • Made of plastic or glass.
  • Plastic ones are disposable.
  • Calibrated: Variety of sizes from 1.0 - 50 ml
  • An inexpensive way to transfer variable volumes precisely.
  • Used with a pipetting device

Measuring Pipet

  • A simple variation of the serological pipet

Capillary Pipet

  • capillary microtube calibrated to deliver a fixed volume

Automatic Pipettors

  • Relatively expensive instruments that are calibrated to transfer specific volumes very accurately and repetitively.
  • Not Disposable.
  • Always used with a disposable pipet tip.


General Rules for the Proper Use of Any Pipet

Three important rules apply to the use of any pipet.

  • 1. Understand how your pipet works, and know its delivery volume is before you use it.
  • 2. Never allow fluid to enter the rubber bulb, pipetting device, or automatic pipettor. To prevent this, a pipet is never turned upside down and never rested on its side. When the pipet is not in your hand, it should be resting in a special stand designed to hold the pipet upright.
  • 3. Never touch the tip of the pipet. By touching the tip, you might come in contact with a toxic substance or you might contaminate the sample.


Automatic Pipettors

Automatic pipettors are a special case. Because they are precisely calibrated, delicate, and relatively expensive, knowing how to use and care for automatic pipettors is very important.

Several rules apply specifically to automatic pipettors:

  • 1. Know the volume limits of the pipettor. Most automatic pipettors are adjustable, i.e., the user can adjust the volume delivery within specified limits. It is important to know those limits before you use the pipet.
  • 2. Never adjust the pipettor above or below the volume limits of the pipettor. Trying to force the adjustment beyond its limits will permanently damage the pipette. Adjustment errors are often due to the user NOT understanding how to read the volume indicator window. So, make sure you know how to read the volume indicator window.
  • 3. An automatic pipettor is to be used only with a proper pipet tip designed for that pipettor. Only the pipet tip should be immersed in fluid. Never get the neck of the automatic pipettor wet.
  • 4. The automatic pipettor should always be facing tip down. Never hold the pipettor upside down, and never place the pipettor on its side on the lab bench. If the pipet tip is not facing down, fluid can run into the pipettor causing contamination, or possible corrosion of the pipettors piston.
  • 5. Never touch and never flame the disposable tip.
  • 6. Never let the plunger snap back after withdrawing or ejecting fluid.