An ICR cell (01) operates with a duplexer (08), which is an integral part of a transmission and receiving device (09) of an FT-ICR mass spectrometry device. The device transmits a transmitter (03) voltage to at least one electrode (11) of the ICR cell during an ion excitation phase and protects a preamplifier (04) from overvoltage. An ion received signal passes through a reception path (12) to the preamplifier during an ion detection phase. The duplexer has at least one active serial switch (07) with two switchable states, each with different series impedances, which is inserted in the reception path (12). As a result, a duplexer for an ICR cell of an FT-ICR mass spectrometry device is provided in which at least one electrode can be used for both ion excitation and for subsequent ion detection.