Abstract: A measuring instrument for reflectometric measurements, comprising a spherical measuring chamber (1) provided with a light source (2) and with a specimen aperture (3); a measuring channel (4) which has been provided with optics (5), with a photometer (6), with an optional stop (7) and with an optional filter (8); a reference channel (14) provided with optics (15), with a photometer (16), with an optional stop (17) and with an optional filter (18); and a signal processing and calculating device (20.sub.s, 20.sub.c) for processing and comparing with each other the light intensity values observed by means of the photometers in the measuring and reference channels. As taught by the invention, the measuring instrument comprises at least one visible light light source (2.sub.s) which emits substantially light having a wavelength mainly over about 380 nm, and a UV light source (2.sub.u) which emits substantially light in the UV range having a wavelength mainly under about 380 nm, advantageously 300 to 380 nm.

Abstract: An electrode system and method, including a measurement electrode, a reference electrode and a counterelectrode, for measuring hydrogen peroxide concentration in a solution. For the measurement electrode, an electrode made from titanium, zirconium, tantalum or niobium is used.