Colors

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UV – VIS spectroscopy Jakub Kovář

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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

A

2,5 2 1,5 1 0,5 0 200 Spectrophotometer

A

 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 