By Bob Wilcox
If you’ve been frustrated from time to time (or lots of times, for that matter) trying to dispense the exact amount of a raw material or any other liquid using calibrated glass tube burettes and pipettes check into bottletop burettes as an alternative. They are especially helpful when using the same reagent over and again.
There are a number of benefits you’ll immediately observe. First of all you won’t ever again have to deal with filling those tiny tubes and possibly spilling ingredients on the lab table. (Not that you have ever spilled anything, of course.) Also you won’t have to worry about menisci calculations. You get exactly what you programmed into the mechanism.
Forget about spending time washing glass tube burettes and pipettes every time you use them. And, oh yes, there’s breakage. You’ll really have to work on breaking a bottletop buret.
Other reasons to consider these dispensing devices:
- Dispense or deliver? Program the bottletop burette for either action
- Superior accuracy from 1 µl to 20µl depending on model
- Flow rates up to 30 ml/min depending on model
- Titration accuracy <=0.1%
- Individual calibration to user-specified adaptations
How a Bottle-Top Burette Works
Bottle-top buret dispensing systems can be hand operated or motor powered and should conform to ASTM E287-02 (2007) Standard Specification for Laboratory Glass Graduated Burets Class A for precision-grade burets. As the name suggests they are screwed to the top of the reagent bottle and by their pumping mechanism draw liquid in the amount programmed on the operating panel.
Whether you select a hand-operated or motor-driven bottletop burette depends on the nature of your work. For example, automated continuous dispensing favors a motor-driven burette operated by a 9-volt DC adapter. Hand-powered models have two AA batteries to display the data.
A great feature of these devices is that they reduce, if not eliminate, dangers associated of manually filling tube burettes and/or pipettes with corrosive or otherwise dangerous liquids. To handle such substances wetted parts of burette pumping mechanisms are constructed of corrosion-resistant materials such as aluminum oxide (Al2O3) and Ethylene tetrafluoroethylene (ETFE). Models such as the Contiburette® systems from CAT Scientific also have electronics isolated from solutions being dispensed, and are manufactured without valves and their associated dead volume in the dispensing mechanism.
Maintaining Bottletop Burettes
A bottletop burette can dispense amounts equal to the capacity of the bottle. Yes, that makes sense, but when bottles run dry or you need to change reagents the mechanism must be cleaned.
1. Drain remaining reagent from the system
2. Place the burette on a container of DI water or alcohol
3. Run the buret to flush out the reagent residue
High-end units can be ordered with a small glass reservoir on the dispensing mechanism to hold a recirculating rinsing solution. Water or alcohol rinses the piston and other components to avoid sticking problems and to flush away contaminants. The reservoir should be kept filled and the liquid should be replaced on a regular basis.
Manually operated bottle-top burettes require manual record keeping in your lab journal. Motor-operated models can be connected to a PC or printer for this important activity. Having said that we will add that manual record keeping is always a good idea. Especially if you get visits from agencies checking into your operations and the computer happens to be down.
Bob Wilcox has represented CAT Scientific’s family of liquid metering, homogenizing, magnetic stirring, and related laboratory equipment since 2002. In addition to heading the sales function in the US he is chief technician for the CAT equipment service organization.