A UV absorption spectrometer comprising: a housing, a controller, and a sensor unit including an ultraviolet light source, an analytical cell with an analytical area therein, an analytical area in running water or an analytical area in a gaseous medium, and an UV wavelength separator including a UV detector, wherein an ultraviolet light in a wavelength range of 200-320 nm emits from the light source through the analytical area to the wavelength separator, and the controller is configured to transform output signals from the UV detector into absorbance values or optical densities for two or more wavelengths in the wavelength range, calculate differences of said absorbance values or optical densities, determine a concentration of a chemical in the solution with calibration constants found for a known concentration of the chemical and said differences of said absorbance values or optical densities, wherein the housing includes a first cylinder which accommodates the UV light source and a first optical means for directing and focusing the light emitted by the UV light source towards the analytical area, a second cylinder which accommodates the UV detector and a second optical means for directing and focusing the light passing via the analytical area towards the UV detector, axes of the first and second cylinders are arranged in parallel while perpendicular to a light travelling path in the analytical area, wherein the UV wavelength separator includes optically opaque walls, a positive lens, four optical filters (83, 85, 87, 89), and four additional UV detectors (84, 86, 88, 90), wherein the four optical filters (83, 85 87, 89) include a first optical filter with a maximum transmission at 288 nm for a 45 degree angle, a second optical filter with a maximum transmission at 296 nm for a 45 degree angle, a third optical filter with a maximum transmission at 312.5 nm for a 45 degree angle, and a fourth optical filter with a maximum transmission at 365 nm for a 45 degrees angle, and wherein the five UV detectors include a first UV detector for measuring UV intensity at 288 nm, a second UV detector for measuring UV intensity at 296 nm, a third UV detector for measuring UV intensity at 312.5 nm, a fourth UV detector for measuring UV intensity at 365 nm, and a fifth UV detector for measuring UV intensity at 254 nm. a housing, a controller, and a sensor unit including an ultraviolet light source, an analytical cell with an analytical area therein, an analytical area in running water or an analytical area in a gaseous medium, and an UV wavelength separator including a UV detector, wherein an ultraviolet light in a wavelength range of 200-320 nm emits from the light source through the analytical area to the wavelength separator, and the controller is configured to transform output signals from the UV detector into absorbance values or optical densities for two or more wavelengths in the wavelength range, calculate differences of said absorbance values or optical densities, determine a concentration of a chemical in the solution with calibration constants found for a known concentration of the chemical and said differences of said absorbance values or optical densities, wherein the housing includes a first cylinder which accommodates the UV light source and a first optical means for directing and focusing the light emitted by the UV light source towards the analytical area, a second cylinder which accommodates the UV detector and a second optical means for directing and focusing the light passing via the analytical area towards the UV detector, axes of the first and second cylinders are arranged in parallel while perpendicular to a light travelling path in the analytical area, wherein the UV wavelength separator includes optically opaque walls, a positive lens, four optical filters (83, 85, 87, 89), and four additional UV detectors (84, 86, 88, 90), wherein the four optical filters (83, 85 87, 89) include a first optical filter with a maximum transmission at 288 nm for a 45 degree angle, a second optical filter with a maximum transmission at 296 nm for a 45 degree angle, a third optical filter with a maximum transmission at 312.5 nm for a 45 degree angle, and a fourth optical filter with a maximum transmission at 365 nm for a 45 degrees angle, and wherein the five UV detectors include a first UV detector for measuring UV intensity at 288 nm, a second UV detector for measuring UV intensity at 296 nm, a third UV detector for measuring UV intensity at 312.5 nm, a fourth UV detector for measuring UV intensity at 365 nm, and a fifth UV detector for measuring UV intensity at 254 nm.