Burettes

Used to dispense and measure a variable amount of a chemical solution in analytical chemistry at the same time, burettes feature a long, graduated glass tube with a stopcock on its lower end for liquid measurement. The stopcock valve is used to control the flow of liquid from the burette in either a steady stream or drop-by-drop. Unlike a pipette, the sample quantity delivered by a burette is changeable. For gas measuring burettes, the stopcock is located at the top of the burette’s glass tube. Digital burettes that deliver exactly measured samples, increasing accuracy and precision, are also available.

Titrations are performed to determine the concentration of a specific substance by adding another substance that interacts with the first to neutralize it or to form another compound. Liquid is slowly dispensed from a burette into a flask or beaker that holds a known amount of the test substance. The burette has a solid glass or PTFE stopcock or other fitting to regulate the flow of the liquid.

The “unknown” substance is mixed constantly (via magnetic stirrer/stir bar or similar method) to ensure that the reaction is complete. Often, the end-point of the reaction is a specific change in the acidity or pH of the liquid; a chemical indicator may be used to produce a color change when the reaction is complete.

Burettes may be designed for single or multiple uses; replacement stopcocks, glassware, and other parts are available for most reusable versions.

Other burette features include:

• Material: Glass or plastic
• Size: Usually from 10 mL to 50 mL capacities
• Graduations: Choice of precision (0.01 or 0.1 mL)
• Certification: Class A or Class B, serialized and non-serialized
• Construction: Single-use or with replacement parts
• Types: Standard or self-filling/automatic
  • Burets with PTFE-plug stopcocks
  • Break-resistant, self-zeroing automatic burets
  • Reservoir fill burets