Estimation of meniscus reading uncertainty in volume calibration of conical volumetric instruments

Abstract

One of the major uncertainty sources during gravimetric volume calibration of laboratory glassware is the meniscus reading. To estimate this uncertainty, the internal diameter of the volumetric instrument at the calibration point must be known. Data for internal diameters are available from international standards for several volumetric instruments with cylindrical meniscus reading section. However, there are another kind of volumetric instruments with conical meniscus reading section, like Imhoff cones, whose internal diameter values are not available. This work aims to show how to overcome this problem through the measurement of the internal diameters with an optical comparator. The calculated correction due to the meniscus setting was also put in nomograms, which allow reading directly the value of the uncertainty contribution and illustrates the changes in the meniscus reading uncertainty contribution as the calibration point changes, unlike what happens with cylindrical laboratory volume instruments.