A probe for measuring a sample solution includes an outer body configured to receive an operational amount of a reference solution, and a sensor assembly including an inner body at least a portion of which is located inside the outer body. A shield is positioned between the outer surface of the inner body and the inner surface of the outer body. The shield is configured to be in contact with the reference solution and extends above the top surface of the reference solution when the probe is filled with an operational amount of the reference solution.