I'm an EE/CS type, and not an ME, but using a "leadscrew" sounds to me like you have
a large mechanical advantage. You might drive the plunger through the bottom of the
beaker before you can shut it down, if you use motor current spiking to trip.
As you're an ME, and therefore must love linkages, why not rig up a spring-loaded plunger,
so it will have some play before trashing the beaker. Then add a limit switch up on the
linkage connection between the motor and plunger, well up out of the fluid. The motor
will still be able to travel a bit without generating huge force, even after the plunger
bottoms out.