Things to Know about Bottletop Burettes
A bottletop burette is a precision dispensing and titrating tool that offers superior accuracy and ease of use compared to volumetric burettes and pipettes. The latter are typically glass tubes with calibration marks on the side. Volumetric burettes have a valve at the bottom allowing researchers to dispense a determined amount of liquid; pipettes are designed to dispense their entire volume.
There are some operating details with volumetric burettes and pipettes that researchers must take into account, not the least of which is filling them with a solution and avoiding spills. Another concern is accurately reading the meniscus that develops on the fluid in the tube. Cleaning the equipment is laborious as well to ensure complete removal of the contents – and to avoid breakage.
CAT Scientific Contiburette® bottle top burettes, which can also serve as pipettes, all but eliminate the many concerns of volumetric burettes and pipettes. Reagents to be dispensed are contained in the bottle – called a reservoir – meaning that constant filling and dispensing from glass tubes is no longer required.
The dispensing mechanism is screwed onto the top of the reagent bottle. Several thread adaptors are available to match bottle sizes.
These instruments are called continuous flow bottletop burettes, but the important point to remember is that “continuous” is defined by the researcher and can be up to the capacity of the reservoir. The amount of reagent dispensed is programmed on the display panel and, depending on the model, can range from 1µl to 20 µl. Flow rates to 30 ml/min are also available depending on the models. Titration accuracy is <-0.1%.
Conformance to standard is important, and in this case the applied standard is Class A of ASTM E287-02 2007) “Standard Specification for Laboratory Glass Graduated Burets.”
CAT Contiburettes are either manually or motor driven. Manual models are operated by a side-mounted crank on the dispensing mechanism and have batteries to power the LED display. Motor-driven models use a 9-volt DC adapter. In all cases dispensing systems are valveless to avoid dead volume.
Buret construction materials are important given that some reagents can be quite aggressive. A good selection is aluminum oxide and ETFE for all wetted parts due to excellent resistance to most lab chemicals. Electronics including the microprocessor control should be completely isolated from reagents being handled
Cleaning bottletop burets is easier than cleaning calibrated glass tubes. The dispensing mechanism is removed from the reservoir and placed into another reservoir containing an approved cleaning solution. The burette is operated to pump the solution through the dispensing mechanism then rinsed with distilled water or a sterilizing liquid. For more maintenance details see our article, ‘Bottletop Burettes Need TLC Too’ on the topic.
Another important maintenance step is periodic recalibration, the steps for which are spelled out in the operator’s manual. This exercise is necessary to maintain accuracy.
Finally for this discussion, one must never forget the importance of record keeping. Use a diary for manually actuated burettes. Motor driven burettes should have provision for connecting to a PC or printer through an interface.
So, in conclusion there are quite a few things to know about bottletop burettes. We have not covered them all here but we do welcome your questions.