A conductivity detector includes a flow channel, an electrode arrangement, and a detector. The flow channel has a tube shape with a channel diameter through which a solution including ion components flows. The electrode arrangement is on the flow channel and includes at least an anode and at least a cathode. The anode and cathode are spaced apart by an electrode gap less than or equal to the channel diameter. The detector is connected to the electrode arrangement to detect electrical conductivity of the ion components.