Use a Bottletop Burette for Accurate Liquid Measurement

A CAT post discussing the importance of temperature control in lab experiments noted the distinction between precision and accuracy.  The same distinction applies to measuring liquid.  Precision can be defined as dispensing the same amount of liquid time after time, suggesting that the equipment is precise.  Accurate dispensing means that the correct amount of liquid is dispensed.  So, if you are precise in your dispensing and the amount being dispensed is incorrect, you are, as we said in our other post, precisely wrong.

Glass tube burettes and pipettes have long been used in the lab for dispensing minute amounts of reagent into a sample in order to get a reaction.  Note I used “minute” here vs. precise or accurate.  Lab personnel saddled with using pipettes and burettes are quite familiar with the difficulty of using this equipment.   Key requirements are a steady hand and sharp eye, dealing with the meniscus, avoiding spillage and breakage, and thoroughly cleaning the tubes after use.  An article in The Scientist noted that “dispensing and titrating fluids remains one of the least sophisticated and most common procedures in the laboratory, responsible for introducing margins of error that are not insignificant when considered over the course of multiple readings.*”

Bottle Top Burettes Deliver Accurate Measurements

Bottletop burettes such as Contiburette ®equipment offered by CAT Scientific are designed to precisely dispense liquids in accurate volumes of 1, 10 and 20 micro liters (µl).  They conform to ASTM E287-02 Class A “Standard Specification for Laboratory Glass Graduated Burets.”  Instead of painstaking filling of pipette or burette tubes researchers simply program the CAT bottletop buret with the amount to be dispensed.   Reagents are kept in large bottles to which the buret mechanism is attached.  Titrating or dosing dispensing quantities and rates are set on the intuitive control panel.

Manually operated units are actuated by a hand crank with programming displays powered by AA batteries; motor-driven burettes are driven by a 9-volt transformer and can be connected to a computer for automated operation and/or record keeping.  Manual or automated, the accuracy is the same.

Typical Operating Procedures

Bottletop burette can dispense amounts equal to the capacity of the bottle. When you need to refill or replace reagents the dispensing mechanism must be cleaned.  Cleaning could be avoided if (a) your SOP permits and (b) you immediately attach a bottle with the same reagent.  Here are suggested procedures:

  1. Pump remaining agent from the intake tubes and pump mechanism.
  2.  Place the burette on a container of DI water or alcohol
  3. Run the buret to flush out the reagent residue

After affixing the pump mechanism to a new container of reagent activate the pump to remove air in the intake tube until no bubbles are observed.  Full details are given in the owner’s manual.

CAT Scientific also offers a motor-driven bottletop buret with an integral rinse port on the dispensing mechanism to hold a rinsing solution.  This recirculates water or alcohol to rinse the piston and other components and flush away contaminants.  The reservoir should be kept filled and the liquid should be replaced on a regular basis.

Calibrate the Burette for Accuracy Assurance

Most if not all precision measuring and weighing devices should be calibrated on a regular basis to maintain their measuring accuracy and correct dispensing errors if noted.  CAT Contiburettes are factory calibrated.  Recalibration procedures should be spelled out in a company’s operations manual following steps outlined in the owner’s manual.

If you need more information on selecting and using CAT bottletop burettes please send us your questions.  We promise to get back to you quickly.

Bob Wilcox

Bob Wilcox has represented CAT Scientific’s family of homogenizers, magnetic stirrers, liquid handling and related laboratory equipment since 2002 when Staufen, Germany-based CAT Ingenieurbüro M. Zipperer GMbH established operations in North America. Bob oversees CAT Scientific laboratory apparatus sales and service organization from the company’s headquarters in Paso Robles, CA. He also is in charge of the parent company’s line of JetCat jet turbines, turboprop, and helicopter power plants for hobbyists’ radio controlled fixed wing and helicopter model aircraft. -- Earlier in Bob’s career he was involved in visual and special effects as well as camera and electronics supervisory responsibilities for the motion picture and television industry.

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