Apparatus 20 for detecting chirality of molecules in a sample comprises an evacuated interaction zone 22 for containing at least one molecule, a radiation source 24 for generating circularly polarised ionising radiation 112 in a forward direction along a propagation axis P that extends through the interaction zone, a magnetic field generator for generating a magnetic field in said interaction zone, directed parallel with the propagation axis, a forward particle detector 40 to detect forward travelling photoelectrons 114F generated by the ionising radiation, and a backward particle detector 42 to detect backward travelling photoelectrons 114B generated by the ionising radiation. The magnetic field confines photoelectrons in the device volume. Deflector electrodes 44, 46 deflect electrons to the detectors. Ion extraction means 56 may direct ions to a particle detector 60. The apparatus can detect both molecular chirality from the forward and backward detector outputs, and chemical identity of a molecule from th
