Preface

Infrared spectroscopy (IR) is a potent spectroscopic technique that has seen considerable developments over the past few decades. With a variety of applications in different fields, IR spectroscopy is becoming an indispensable analytical technique. Its ease of operation, its non-destructive nature, and its capability to elucidate structures of both organic and inorganic materials make IR exceptionally attractive for numerous applications. The typical applications of IR spectroscopy include the identification of functional groups, anomeric carbon structures, crystal allomorphs, and more. Because some structures are so similar, the qualitative characterization of these compounds using IR spectroscopy is a challenging task. Furthermore, the overlap of bands in spectra might obscure relevant information. As a result, qualitatively analyzing different compounds using only one characteristic IR peak may be purely empirical and inaccurate.

This book introduces the basic principles of IR spectroscopy with a focus on recent advances and applications. It includes ten chapters that examine the applications of IR spectroscopy in different disciplines. Chapter 1 by Dr. El-Azazy et al. discusses the basic principles of IR spectroscopy, the most common assignments of the different functionalities required by researchers, and the implementation of IR spectroscopy in different applications. Chapter 2 by Dr. D.T. Hallinan Jr. presents a tutorial on the attenuated total reflectance (ATR) mode of Fourier-transform infrared (FT-IR) spectroscopy and how it can be used to measure transport through polymer membranes. In addition to covering the experimental setup and time-resolved data processing, this chapter presents fundamental equations for analyzing data to obtain diffusion coefficients. Chapter 3 by Dr. Prasanta Das investigates the instrumentation of gas phase FT-IR and its recent advancements and applications. The chapter focuses on the principle and data acquisition scheme of the repetitive mode measurement method of an FT-IR spectrometer. Chapter 4 by Prof. Dr. Nabeel Othman discusses both the qualitative and quantitative applications of IR spectroscopy. Chapter 5 by Sonia Nieto-Ortega et al. discusses the application of near IR spectroscopy (NIRS) in the food sector, especially for the fish value chain, combined with several chemometric techniques for quality, authenticity and safety applications. Chapter 6 by Dr. Chen et al. examines the applicability of functional NIRS (fNIRS) in monitoring brain activities to avoid stroke. Chapter 7 by Dr. Maggy et al. discusses the ability of NIR/MIR to provide fast and reliable estimates on subjects related to vector-borne diseases. Chapter 8 by Dr. El-Azazy et al. highlights the applications of FT-IR in the characterization of lignocellulosic biomasses and its impact on the depollution capacity for wastewater treatment. Chapter 9 by Aulia M T Nasution et al. discusses the employment of IR spectroscopy for detecting adulterants in food and traditional Indonesian herbal medicine. Finally, Chapter 10 by Dr. Barrera-Ortega et al. explores the application of Raman spectroscopy for dental enamel surface characterization.

I would like to thank my co-editors Prof. Khalid Al-Saad and Dr. Ahmed El-Shafie for their great efforts in reviewing and editing this book. I am indebted to all the

authors for helping me to accomplish this project and who have contributed excellent chapters. All authors are experts in their fields and have tried their best to disclose the inherent concepts related to any of the mentioned applications. Their efforts to make this book comprehensive and informative are much appreciated.

**Chapter 1**

Applications

From Eqs. (1) and (2),

or in wavenumbers (400–4000 cm�<sup>1</sup>

**1. Spectroscopy**

Introductory Chapter: Infrared

*Marwa El-Azazy, Ahmed S. El-Shafie and Khalid Al-Saad*

Spectroscopy is a term used for the study of the spectra generated as a result of interaction of electromagnetic radiation with matter. It is used for the detection and/ or identification of atoms, molecules, functional groups, and nuclei based on the produced spectra following the interaction of matter with the radiation. When light strikes matters, it can physically be reflected, refracted, scattered, or transmitted. During transmittance through matter, light with specific energy may interact with molecules in different ways, depending on the energy (E, Joule) of lights, which is directly proportional to its frequency (υ, with the unit sec�<sup>1</sup> or Hz) and inversely proportional to wavelength (λ) as according to the equations below-mentioned:

Energy, E ¼ h*:*υ (1)

Frequency, υ ¼ C*=λ* (2)

E ¼ h*:*C*=λ* (3)

E ¼ h*:*C*:*ῡ (4)

, for the mid-IR (MIR) region). Schematic

Spectroscopy - Principles and

where h is Planck's constant (6.6260755 � <sup>10</sup>�<sup>34</sup> <sup>J</sup>�s)

where c is the speed of light (2.998 � <sup>10</sup><sup>8</sup> m/s in vacuum).

Expressing 1/λ as wavenumber (ῡ), Eq. (3) can be described as below:

description showing other electromagnetic regions of the spectrum, along with molecular processes rising from the interactions in each region, is illustrated in **Figure 1**. Matter may interact with light of microwave region causing the rotational movement of entire molecule. Light of particular energy in the IR region may cause the vibrational movement of bonds in the molecules, including stretching, bending,

Based on the above relationships, the energy of light can be scaled on a sector of spectrum by the unit of wavelength (300–700 nm, in UV–visible spectrophotometry)

I am most grateful to Author Service Manager Ms. Romina Rovan at IntechOpen for her efforts and support throughout the process of editing this book. Many thanks to the entire IntechOpen publishing team for making this book possible.

> **Dr. Marwa El-Azazy, Dr. Ahmed S. El-Shafie and Prof. Khalid Al-Saad** Department of Chemistry and Earth Sciences, College of Arts and Sciences, Qatar University, Doha, Qatar

## **Chapter 1**
