Xjyuk

As an analytical chemist, I'm always ensuring my glassware is thoroughly clean before I start an analysis. However, my supervisor always states that using ultrasonic bath to clean volumetric glassware damages its calibration, rendering it imprecise for analytical usage. Does that hold true, or is it okay to use an ultrasonic cleaner?

According to technical information for volumetric measurement provided by Brand, it is acceptable to use an ultrasonic bath.

Both glass and plastic labware may be cleaned in an ultrasonic bath. However, direct contact with the sonic membranes must be avoided.

Nevertheless,

For gentle treatment of labware, clean immediately after use – at low temperatures, with brief soaking times, and at low alkalinity. Glass volumetric instruments should not be exposed to prolonged immersion times in alkaline media above 70 °C, as such treatment causes volume changes through glass corrosion, and destruction of graduations.

If your supervisor is unconvinced by Brand's guidance on this (as supplied by Loong in his answer), you could always test the effect of ultrasonic cleaning directly:

Take, say, six volumetric flasks, and weigh the amount of water each holds when filled to the line. Then subject three to several cycles of ultrasonic cleaning (the other three can be left to sit in the ultrasonic cleaning solution, but without turning the machine on), dry all six, and repeat the weighing measurement. Determine if the before-and-after difference for the ultrasonically cleaned flasks is significantly different from that seen in the control flasks.

While the control flasks do control for temperature differences between the before-and-after measurements, it would be cleaner if you could do the before-and-after measurements at the same temperature. That way the only difference you see should be random experimental error plus any systematic differences due to cleaning.