ColorsUV – 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 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 Since UV-VIS

spectroscopy is an absorption technique, Lambert - Beer's law can be applied

Spectrophotometer lcA

0log

Absorpční spektrum benzenu

0

0,5

1

1,5

2

2,5

3

200 220 240 260 280 300 320 340 360

(nm)

A

plynný kapalný

Vocabulary

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