Frequently Asked Questions
Volumetric glassware is intended for the precise and accurate measurement of fluid volumes. Glassware is calibrated either To Contain (TC) or To Deliver (TD), accounting for the amount of fluid remaining in the container due to the surface tension of water. ISO standards refer to To Contain as “IN” and To Deliver as “EX.” Some glassware is marked with two calibration lines so that the same container can be used for both To Contain or to Deliver applications.
There are many different options available with Volumetric flasks. First, we have the volumetric tolerance the flask is calibrated to (such as Class A or B). Class A has the tightest tolerances for analytical applications, whereas Class B tolerances are often used in education. Next, if your solutions are light sensitive, choose either an amber glass flask or a Ray-Sorb treated flask. Ray-Sorb flasks have the lowest level of visible and UV light transmission. Depending on your application, selecting a wide-neck flask (larger diameter neck) is helpful for adding tablets to the flask or speed filling and emptying. However, with the wider neck, you sacrifice accuracy and precision (about a two-fold decrease in tolerance). For mixing applications, a flask with a bulb in the neck significantly improves mixing with viscous solutions.
Volumetric flasks are tooled for ground glass joints for tapered flask stoppers, threads for screw caps, or glass rims for snap caps. The tapered flask stoppers are available in glass, polyethylene, polypropylene, or PTFE. The choice of stopper type needs to be made in conjunction with the kind of solutions that will be mixed in the volumetric flask to ensure chemical compatibility. Glass and PTFE stoppers have the widest chemical compatibility. Please note that the tapered flask stoppers defined in ISO 1042 and ASTM E288 (the two standards defining volumetric flasks) differ in the dimensions of the stoppers used for each volume range.
Two key standards cover volumetric flasks: ASTM E288 (Standard Specification for Laboratory Glass Volumetric Flasks) and ISO 1042 (Laboratory glassware — One-mark volumetric flasks). Within North and South America, the ASTM standard is usually followed, while the ISO standard is more common in Europe, Asia, and the rest of the world. ASTM E288 has slightly tighter tolerances for the glassware. Both standards define the type of glass (33 expansion borosilicate glass) through the reference to other standards for scientific glassware (such as ASTM E438 and ISO 719). Both standards define two classes of accuracy (Class A and B), with Class B having twice the tolerance of Class A. Both standards define standard (narrow neck) and wide neck flasks in terms of construction details and volumetric tolerances. Calibration of volumetric flasks is covered by ASTM 542 and ISO 4787, respectively.