UV-Visible and Infrared Spectroscopic Methods in Environmental Analysis - Fundamentals of Environmental Sampling and Analysis - page 191

determine concentrations. The discussions on structural (qualitative) analysis using
IR are kept at the minimum due to its technical complexity and specialized
applications only to certain professionals.

8.1 INTRODUCTION TO THE PRINCIPLES
OF SPECTROSCOPY

8.1.1 Understanding the Interactions of Various
Radiations with Matter

Spectroscopy is a subject that deals with the interaction of electromagnetic radiation
with matter. All qualitative and quantitative determinations using spectroscopic
methods need radiation to pass through the sample containing the analyte of interest
(the matter). Radiation is defined by its wavelength or frequency, which is related to
the energy of the radiation by the planck's law :

E ¼ hn ¼ hc= l ð8 : 1Þ

6210 34 Js) and c¼ speed of light ( 310 8 m/s).
The wavelength ( l ) is the distance between two adjacent peaks of electro-
magnetic radiation, and may be designated in m, cm, nm, or

where h¼ Planck constant ( 6 :

m m(1m ¼

10 2 cm ¼ 10 6 m ¼ 10 9 nm). Frequency ( n ) is the number of wave cycles that

travel past a fixed point per unit time and is usually given in cycle per second or
hertz (Hz). Wavelength is inversely proportional to the frequency. The energy of
radiation ( E ) increases with the increasing frequency and increases with
decreasing wavelength (Eq. 8.1).
Figure 8.1 is an electromagnetic spectrum containing the wavelength regions
with a variety of analytical applications. The energy per photon is in an increasing
order: radio wave

m

< microwave < infrared (IR) < visible light (VIS) < ultraviolet

(UV) X-ray. Our naked eyes can detect only a very limited range of wavelengths,

that is, the visible spectrum from about 300 to 780 nm.

<

Wavelength (m)

1 nm

1 mm 1 m

10 -11 10 -9 10 -5 10 -3 10 -1 10 1 10 -7

X-Ray

Infrared

0.1-100 ο

780 nm-1 mm
(12820-10 cm -1 )

Radio wave
1 mm-1 m
(300 GHz-300 MHz)

Α

Ultraviolet

10-380 nm

Visible

380-780 nm

NMR
0.3 m - 10 m
(900 - 30 MHz)

Figure 8.1 The electromagnetic spectrum (wavelength unit: 1m¼ 10 2 cm¼ 10 3 mm¼ 10 9 nm¼
10 10 A; frequency unit: 1Hz ¼ 1s 1 ¼ 10 6 MHz ¼ 10 9 GHz; wavenumber has a unit of cm 1 )