Transcript Colours UV – VIS spectroscopy
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 just a small part of the electromagnetic spectrum which extends from radio waves (long waves) to gamma rays (10 -3 meters down to 10 -15 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 3 Since UV-VIS spectroscopy is an absorption technique, Lambert Beer's law can be applied
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2,5 2 1,5 1 0,5 0 200 Spectrophotometer
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log 0
c l
220
Absorpční spektrum benzenu
240 260 280
(nm)
plynný 300 kapalný 320 340 360
Vocabulary Prism - krystal Hue - odstín Saturation - sytost Brightness – světlost Rain bow – dešťová poklona