The Materials Handler, also known as the sample cart, is a device used by Black Mesa scientists to deliver material samples (such as Xen crystals) to Sector C's Test Lab C-33/a where they are analyzed by the Anti-Mass Spectrometer.
Samples are held by the cart's pincers while a scientist must push the instrument to its intended destination. On the day of the fateful experiment, Gina Cross brings the sample cart holding sample GG-3883 into the lift below the test chamber. Above, Gordon Freeman puts it into the Anti-Mass Spectrometer's beam, triggering the Resonance Cascade. The cart was completely destroyed during the ensuing devastation.
 Behind the scenes
The Materials Handler was designed to resemble a futuristic shopping cart.
The Materials Handler waiting for Gina Cross in Decay.
The Anti-Mass Spectrometer with the cart on the right in Half-Life.