Volumetric Flasks with Stopper

A volumetric flask is the gold standard for making up a solution to an exact volume. Its single fine ring on a narrow neck means there is only one precisely calibrated graduation, read at the meniscus, so filling to that line gives a highly accurate, repeatable volume — the basis of preparing standards and accurate dilutions.

The long narrow neck is deliberate: a small change in liquid height there is a tiny change in volume, so the fill point can be hit precisely. Class A flasks carry the tightest tolerances and a certificate.

Preparing standards and solutions to an exact concentration, accurate dilution, quantitative analysis and calibration standards, in analytical, QC, pharma, food-testing and environmental labs. Amber flasks are used for light-sensitive standards.

A pear-shaped borosilicate 3.3 body with a long narrow neck bearing a single calibration ring, and a matched ground-glass or plastic stopper. Class A flasks are made to tight tolerances and certified; they are calibrated 'to contain' (TC) the nominal volume at a stated reference temperature (commonly 20 °C).

Fill to the ring with the bottom of the meniscus on the line at eye level, at the calibration temperature for best accuracy. Do not heat volumetric flasks or use them for hot liquids, as this changes the calibrated volume; mix by inverting with the stopper held in. Keep the matched stopper with its flask.

Formed from borosilicate 3.3 with the pear body, long neck and ground joint, then annealed. The single calibration ring is applied after the flask is calibrated against reference standards; Class A flasks are individually or batch-certified. Calibration accuracy and joint fit are the key checks.