An analytical tool suitable for mounting to an analytical apparatus, the analytical tool comprising a substrate, a cover, and a spacer between the cover and the substrate, wherein the substrate, the spacer and the cover define a capillary extending in a longitudinal direction of the substrate, wherein the capillary forms a flow path for moving a sample, the capillary comprising an introduction port for introducing the sample into the capillary, and wherein the analytical tool further comprises a working electrode and a counter electrode for applying a voltage to the sample supplied to the flow path, the working electrode and the counter electrode being formed on the substrate; wherein the working electrode comprises a first active portion which is positioned within the flow path for coming into contact with the sample and an exposed contact end which is positioned outside the flow path for contact with a first terminal of the analytical apparatus, and the counter electrode comprises a first portion, wherein the first portion includes a second active portion which is positioned within the flow path for coming into contact with the sample and an exposed contact end which is positioned outside the flow path for contact with a second terminal of the analytical apparatus; wherein the analytical tool comprises no further contact ends, other than the exposed contact end of the working electrode and the exposed contact end of the counter electrode, the contact ends (15a, 16a) for contacting the working electrode and the counter electrode with the first and second terminals (20, 21) of the analytical apparatus; characterized in that the counter electrode further comprises a second portion formed on the substrate, the second portion including a third active portion and a fourth active portion both positioned within the flow path, wherein the third active portion is positioned on one side of the first active portion and the fourth active portion is positioned on the opposite side of the first active portion, the second portion is divided physically and electrically from the first portion, whereby the fourth active portion is divided physically and electrically from the second active portion by a slit extending in the longitudinal direction of the substrate within the flow path, and the third active portion, the first active portion and both of the second active portion and the fourth active portion are arranged in the mentioned order from the introduction port along the sample flow direction in the flow path. the analytical tool comprising a substrate, a cover, and a spacer between the cover and the substrate, wherein the substrate, the spacer and the cover define a capillary extending in a longitudinal direction of the substrate, wherein the capillary forms a flow path for moving a sample, the capillary comprising an introduction port for introducing the sample into the capillary, and wherein the analytical tool further comprises a working electrode and a counter electrode for applying a voltage to the sample supplied to the flow path, the working electrode and the counter electrode being formed on the substrate; wherein the working electrode comprises a first active portion which is positioned within the flow path for coming into contact with the sample and an exposed contact end which is positioned outside the flow path for contact with a first terminal of the analytical apparatus, and the counter electrode comprises a first portion, wherein the first portion includes a second active portion which is positioned within the flow path for coming into contact with the sample and an exposed contact end which is positioned outside the flow path for contact with a second terminal of the analytical apparatus; wherein the analytical tool comprises no further contact ends, other than the exposed contact end of the working electrode and the exposed contact end of the counter electrode, the contact ends (15a, 16a) for contacting the working electrode and the counter electrode with the first and second terminals (20, 21) of the analytical apparatus; characterized in that the counter electrode further comprises a second portion formed on the substrate, the second portion including a third active portion and a fourth active portion both positioned within the flow path, wherein the third active portion is positioned on one side of the first active portion and the fourth active portion is positioned on the opposite side of the first active portion, the second portion is divided physically and electrically from the first portion, whereby the fourth active portion is divided physically and electrically from the second active portion by a slit extending in the longitudinal direction of the substrate within the flow path, and the third active portion, the first active portion and both of the second active portion and the fourth active portion are arranged in the mentioned order from the introduction port along the sample flow direction in the flow path.