How to Avoid Meniscus Measuring Errors
Glass tube lab pipettes and burettes are capable of precisely dispensing reagents into samples but require outstanding patience and an accurate eye to take into account the meniscus of the reagent. Most menisci are concave or U-shaped with the liquid in contact with the tube wall reading higher than at the center. This property characterizes aqueous solutions. Other liquids, mercury for example, exhibit convex menisci with the higher portion at the center rather than at the tube wall.
Whether concave or convex, the meniscus must be accommodated in your reagent volume calculations. For concave menisci read the volume from the bottom of the curve; for convex read from the top. Trouble is, you have to carefully fill the pipette or burette and carefully hold it steady and carefully eyeball the liquid level directly on, not from an angle. And, after all is done, you have to carefully clean the equipment and ready it for the next measuring exercise.
End the Fuss and Bother with a Bottletop Burette
Pipettes and glass tube burettes will always have a place in the research lab. But when titrating procedures are ongoing you should seriously consider automating the process with bottletop burettes such as available from CAT Scientific. These handy devices are affixed to the top of a bottle holding a large amount of reagent. All you have to do is program the amount of reagent to dispense and the bottle-top burette does the rest!
The fact that you don’t have mess with meniscus calculation is reason enough to consider a CAT Scientific Contiburette®. And to top it off you have a choice of models. Select a manual Contiburette for dispensing in volumes of µ10 or µ20, or a motor driven model for dispensing in volumes of µ1 µ10 or µ20. If you’re handing difficult reagents you should consider a motor driven Contiburette with its own rinse port that circulates a cleaning solution throughout the burette pump. This model dispenses in µ10 or µ20 volumes.
All meet ASTM Class A standard for burettes, all are easily cleaned, all provide for recording and archiving operations and all are equipped with a drying tube connection, a valveless dosing system and can be calibrated to your requirements.