Properly calibrated and performing volumetric glassware (e.g., pipets, burets and volumetric flasks) is essential to obtaining accurate analytical data and results. Even Class A volumetric glassware is not absolute but rather has a tolerance from its stated nominal value. For example, a 25 mL Class A Transfer Volumetric Pipet has a capacity tolerance of ± 0.03 mL, and a 50 mL Class A Buret has a tolerance of ±0.05 mL at full capacity. In addition, volumetric glassware is calibrated at a specific temperature, usually 20°C, but quite often it is used to deliver or contain volumes at a different temperature. These temperature variations make it necessary to adjust samples and/or standards to the calibration temperature before measurement, or to apply temperature corrections to the volumes measured. Glassware that is designed to deliver specific volumes also may have a specific drain time associated with its calibrated volume and must be scrupulously cleaned to drain properly. Therefore it can be seen that variances in volumetric measurements can be a major, if not the chief, source of error in an analytical laboratory.
All Class A volumetric glassware used at RICCA CHEMICAL COMPANY is calibrated before its first use and recalibrated periodically in accordance with ASTM Standard E 542 and NIST Calibration Procedure Number NBSIR 74-0461. All approved volumetric glassware used is certified to comply with the Class A tolerance requirements of ASTM Standard E 288 and to Federal specifications in NIST Circular Number 434. This calibration check before use is necessary because glassware is occasionally obtained that does not meet the Class A specifications as marked. Such glassware is returned to the supplier or discarded.