Colors  UV – VIS spectroscopy Jakub Kovář  Jiří Stančík

Color and light The starting point of an understanding of color is a description of light. White light is actually made up of a whole range of colours, mixed together We can see this if we pass white light through a glass prism

Light spectrum The colors produced by light passing through a prism are arranged in a precise array or spectrum from red through orange, yellow, green, blue, indigo and into violet The intensity of light as a function of wavelength is called light spectrum

Light spectrum The visible spectrum of light is just a small part of the electromagnetic spectrum which extends from radio waves (long waves) to gamma rays (10 -3 meters down to meters, the size of the nucleus)

The color of objects Color is produced by the absorption of selected wavelengths of light by an object The receptors of the human eye only respond to light in the visible spectrum

Mixing of colors RGB model uses red, green and blue color CMYK model uses colors: cyan, magenta, yellow and black Basic characteristics of colors are: hue, saturation, brightness

UV – VIS spectroscopy Analytical method Light is a form of electromagnetic radiation This radiation contains radio waves, visible light and X-rays Light rays are composed of photons whose energy specifies a color from red to violet A visible spectrum has many colors, and a rainbow is a typical spectrum

Wavelenght of colors in UV – VIS spectrum Visible region: 380 – 700 nm Violet: 400 nm Blue: 480 nm Green: 500 Yellow: 580 nm Orange: 600 nm Red: 700 nm

Scheme of spectrophotometer

Description of spectrophotometer Source of radiation(tungsten lamp, laser …) Monochrome (prism, graticule…) Sample compartment(cuvette with sample) Detector (diode-array detector)

Principles of spectroscopy Spectrometer exposes a chemical solution to the UV – VIS light across the electromagnetic spectrum from about 300 to 800 nm A detector then measures the amount of light transmitted through the solution The amount of light reached by the detector is then recorded as a spectrum

Theory Since UV-VIS spectroscopy is an absorption technique, Lambert - Beer's law can be applied Spectrophotometer

Vocabulary Prism - krystal Hue - odstín Saturation - sytost Brightness – světlost Rain bow – dešťová poklona