How to Use Mohr Pipettes

According to the book,"Analytical Chemistry for Technicians," Mohr pipettes are measuring devices that have multiple graduation lines, so you can use them to measure and dispense volumes of liquid that you cannot do with a standard volumetric pipette. Named after the 19th-century German pharmacist Karl Friedrich Mohr who, according to the Smithsonian, developed his pipettes to transfer specific amounts of liquids with as much accuracy as possible. Mohr pipettes are somewhat counterintuitive as the graduation marks go from high to low as you draw in fluid, thus requiring some minor calculations prior to dispensing.

Instructions

• 1

  Insert the non-tapered end of the Mohr pipette into your pipette aid, so that it fits snugly and is able to remain inserted without you having to hold the pipette itself.

• 2

  Draw up the fluid you want to transfer vertically into the Mohr pipette using the pipette aid, so that the the bottom of the curve created by the top of the fluid (also known as the meniscus) is precisely at the top graduation mark. No matter what size Mohr pipette you are using, the top graduation mark on it will be 0 milliliter (ml).

• 3

  Determine, based on the amount of fluid you want to transfer, at which graduation mark on the Mohr pipette you should stop the meniscus of the fluid while you are dispensing. For example, if you want to transfer 6 ml of fluid from a full 10 ml Mohr pipette, you will want the meniscus to stop at the 6 ml graduation mark.

• 4

  Dispense the fluid in your Mohr pipette using the pipette aid, stopping when the meniscus reaches the graduation mark that corresponds to the volume of fluid you want to transfer.