Calibrating a Bottletop Burette
When to Calibrate a Bottle Top Burette
Let’s start with why we should calibrate a bottle top burette. Bottletop burets are designed to precisely meter reagents into a vessel until a reaction occurs. Accuracy is paramount, and in the case of burettes we’re talking in increments of micro liters (µl). Bottletop burettes are mechanical devices and as such are subject to wear. Wear eventually affects accuracy. (Glass tube burettes controlled by a hand-operated valve at the base must also be checked for accuracy as the valve itself may wear.)
While burets such as the Contiburette series available from CAT Scientific are fabricated of extremely corrosion- and wear-resistant pumping components ISO 9000 “Monitoring of Test Apparatus” and general Good Laboratory Practice (GLP) call for periodic re-calibration to confirm accuracy or correct inaccuracy. The frequency of recalibration depends on operating conditions, and should be spelled out in your company’s operating procedures. Exceptions that could result in more frequent recalibration include significant changes in reagent formulation or if the burette is knocked over or otherwise subjected to rough handling.
A Brief on Bottletop Burette Calibration Procedures
The intricacies of bottle top buret recalibration are beyond the scope of this post. Instead we provide a brief on how the activity is accomplished. Complete details and formulae are provided in CAT Contiburette operating manuals and in ISO 8655-6:2002. This standard specifies the gravimetric determination of errors of measurement for conformity testing of piston-operated volumetric apparatus.
The key elements are the weight and volume of the liquid being used in the calibration exercise, and the temperature at which the exercise is undertaken. Temperature has an effect on the density or weight of the water being used in the exercise. An essential component of a recalibration exercise is an analytical balance that also calibrated for accuracy.
CAT Contiburettes are factory calibrated with distilled water. Unless you are dispensing reagents with significant differences in density distilled water can be used for calibration checking. Here are the steps to be undertaken:
- Fill the Contiburette bottle with distilled water and dispense it into a separate container until the tube is bubble-free.
- Set the display to zero and dispense 5 ml into a separate vessel, then weigh it with the precision balance.
- Calculate the volume taking temperature into account.
- Repeat steps 2 and 3 at least 10 times.
- Calculate the accuracy (A%) and coefficient of variation (CV%) using the statistical computation formulas provided in the instruction manual
If recalibration is required the Contiburette can be adjusted by following directions for the internal user calibration program.
Instructions are likewise provided to return the unit to its factory calibrated setting.