Burette Glossary of Terms

A Bottle-Top Burette Glossary of Terms

Scientific instruments including metering and dispensing equipment such as bottle top burettes have their own nomenclature.  For the uninitiated this can cause vexation as one struggles to understand what is being talked about.   We at CAT Scientific think it is helpful to provide definitions of terminology applied to bottletop burets.  The following listing covers the more common terms, but you are welcome to ask us a question if you are unclear about terms related to operating a bottletop burette.

Burette:  A logical place to start.  Burettes (also spelled burets) are designed to meter out precise amounts of a liquid, generally called reagents, into a vessel to perform a chemical analysis. Glass tube burettes are controlled by a stopcock valve located at the base of the tube so researchers can precisely control the dispensing operation.  (See Pipette)

Bottle-Top Burettes:  Dispensing operations, whether metering or continuous, are controlled by a motor driven or hand operated mechanism affixed to a bottle containing the reagent.  The amount of reagent dispensed can be programmed, and is shown on an LED display.  As with glass tube burets they are extremely accurate, but have the advantage of simplifying cleaning operations when switching reagents (see Cleanability).  They also eliminate the challenges of filling glass tube burettes and of accurately reading the reagent meniscus. (See Meniscus)

Bottle Adaptors: Also called reservoir adaptors, they provide flexibility in mounting bottletop burets to different sized reagent bottles.

Calibration: The process of determining the accuracy of a bottle top burette and correcting dispensing errors if noted.  CAT Contiburettes are factory calibrated but good laboratory practice (see GLP) calls for recalibration on a regular basis that should be spelled out in a company’s operations manual.  Calibration procedures are outlined in the owner’s manual.

Cleanability:  As the word suggests this relates to how burettes are cleaned.  Glass tube burettes are extremely labor-intensive as they require frequent cleaning involving multiple rinses before being used for a different reagent.  Bottletop burettes are easily cleaned by attaching them to a reservoir containing DI or distilled water and running the pumping mechanism.  This can be followed by an alcohol rinse for sanitation if required. (See Self-Cleaning Burettes)

Data Transfer:  Regulatory authorities require that records be kept relating to many laboratory operations.  Labs using hand powered bottletop burettes should have a logbook in which all data are entered.  Motor-driven burettes can be connected via an RS485 interface to a computer or printer. (See RS Interface)

Drying Tubes:  Some reagents react adversely to moisture in air that replaces them as they are drawn out of the bottle during metering operations.  To remove moisture incoming air passes through a drying tube filled with a drying reagent and stopped with cotton at each end.  The tube is connected to the burette dispensing mechanism to allow treated air to enter the bottle.

Flow Rate: The rate in milliliters per minute at which burette pumps dispense reagents.  Note that this is not to be equated with dispensing subdivisions (see Pumps).

GLP:  Good Laboratory Practice.  GLP is a set of procedures to assure uniformity, consistency, reproducibility and other control systems in laboratories and similar settings.  GLP criteria are generally set by government agencies and trade associations as an important part of quality control procedures.

Meniscus: The curve in the upper surface of a liquid in a tube such as a pipette or glass tube burette.  It can be either convex or concave, depending on the surface tension of the liquid.  Accurate measuring of the volume of a pipette or glass tube burette requires taking the meniscus into account.  Meniscus calculation is not required when using bottletop burettes.

Pipette: A pipette (pipet, pipettor) is a glass tube with etched gradations showing a volume of liquid such as a reagent.  Unlike a burette, a pipette is usually employed to dispense its entire content rather than a metered amount.   Filling a pipette with the exact amount of reagent is an exacting task that has to take the meniscus into account.  (See Meniscus)

Power Supply: Hand-operated burettes, designated by an H in the CAT lineup, are operated by turning a hand crank.  They contain two AA batteries for programming and to power flow rate and volume indicators.  Motor-operated models, designated by a D, are powered by a 9-volt transformer connected to an electrical outlet.  Both offer the same accuracy.  The higher-cost motor driven models are generally used for continuous operations and can be controlled by computers thereby freeing personnel to handle other tasks.

Pumps:  High-precision pumps either hand or motor actuated are the heart of bottletop burette assemblies and are designed to dispense in micro liter (µl) subdivisions.  Subdivision options for CAT Contiburette bottletop burettes are 1µl, 10µl and 20µl.  Note that these are the smallest amounts that are dispensed at one pump stroke and should not be equated to flow rate (see Flow Rate).  The upper limit of dispensing is governed by the capacity of the reagent bottle and controlled by programming the burette to the desired amount.

Pump Construction: Purchasers of bottletop burettes should pay particular attention to pump materials of construction due to the highly corrosive nature of many reagents.  It is strongly recommended that all wetted parts are made of aluminum oxide (Al2O3) and transparent polymer Ethylene tetrafluoroethylene (ETFE), and that system electronics are totally isolated from reagents.   It is also recommended to avoid bottletop burets that have valves because valves can create dead volume and can bind due to corrosion.

RS Interface:  An RS232 and/or RS485 interface is used to control the operation of and collect data from motor-operated bottletop burettes.  See Data Transfer.

Self-Cleaning Burettes: Higher end bottletop burettes can be ordered with a self-cleaning feature.  The dispensing mechanism has its own pump and small container for distilled water or alcohol.  When activated, the cleaning solution pump recirculates solution through the burette dispensing pump to rinse out the reagent.

Titration: Titration is the objective of using burettes or pipettes.  It is the means by which researchers determine the concentration of a solution by adding the reagent in a measured quantity until a reaction occurs – such as a change in color.

Valveless Construction: Valves in dispensing mechanisms can introduce what is called “dead volume” that impacts the accuracy of bottletop burettes.  Instead, precision pumping configurations assure continuous accuracy during metering and dispensing operations. See Pump Construction.


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