Abstract: A sensor and a method are disclosed for the potentiometric determination of the ion content or activity of a sample and the concentration of other components (e.g., glucose, urea, triglycerides, enzymes, drugs) of a sample. The sensor comprises ion-selective electrodes which are held in a frame and have porous material between them; the porous material provides a means to establish ionic flow between the electrodes. Each ion-selective electrode is comprised of a membrane which is selectively permeable to the ion or other substance whose activity or concentration is being determined; a reference electrode; and an internal reference material.