Impedance flow cytometry apparatus comprising: a flow channel for carrying a flow of fluid comprising particles suspended in an electrolyte from an inlet to an outlet ; a first electrode group and a second electrode group , each electrode group providing first and second current paths through fluid flowing in the flow channel; the apparatus characterized in that , each electrode group comprises: a first signal electrode to provide to the first current path a first electric signal of frequency, magnitude and phase; a second signal electrode to provide to the second current path a second electrical signal of substantially equal frequency and magnitude as the first electrical signal and of opposite phase to the first electrical signal; and one or more measurement electrodes to detect current flow in the first current path and the second current path and produce a summed signal representing the sum of the current flow in the first current path and the current flow in the second current path; wherein the first electrode group produces a first summed signal and the second electrode group produces a second summed signal; and in that it further comprises a circuitry to determine a differential signal representing the difference between the first summed signal and the second summed signal. a flow channel for carrying a flow of fluid comprising particles suspended in an electrolyte from an inlet to an outlet ; a first electrode group and a second electrode group , each electrode group providing first and second current paths through fluid flowing in the flow channel; the apparatus characterized in that , each electrode group comprises: a first signal electrode to provide to the first current path a first electric signal of frequency, magnitude and phase; a second signal electrode to provide to the second current path a second electrical signal of substantially equal frequency and magnitude as the first electrical signal and of opposite phase to the first electrical signal; and one or more measurement electrodes to detect current flow in the first current path and the second current path and produce a summed signal representing the sum of the current flow in the first current path and the current flow in the second current path; wherein the first electrode group produces a first summed signal and the second electrode group produces a second summed signal; a first signal electrode to provide to the first current path a first electric signal of frequency, magnitude and phase; a second signal electrode to provide to the second current path a second electrical signal of substantially equal frequency and magnitude as the first electrical signal and of opposite phase to the first electrical signal; and one or more measurement electrodes to detect current flow in the first current path and the second current path and produce a summed signal representing the sum of the current flow in the first current path and the current flow in the second current path; wherein the first electrode group produces a first summed signal and the second electrode group produces a second summed signal; and in that it further comprises a circuitry to determine a differential signal representing the difference between the first summed signal and the second summed signal. <EOS>