Chemical Analysis and Material Characterization by Spectrophotometry

Book Preface

Spectroscopy is a branch of science (analytical chemistry) which deals with the study of the interaction of electromagnetic radiation with matter. In fact, traditionally, the interactions of analyte were between matter and electromagnetic radiation, but now spectroscopy has been broadened to include interactions between matter and other forms of energy. Such examples include beams of particles such as ions and electrons. These kinds of analytical methods that are considered to be one of the most powerful tools available for the study of materials’ fundamental properties (e.g., atomic and molecular structure, optical properties) and also used in quantifying the wide range of chemical species prevailing in a given sample. In this method, an analyst carries out measurements of light (or light-induced charged particles) that is absorbed, emitted, reflected or scattered by an analyte chemical or a material. Then these measured data are correlated to identify and quantify the chemical species present in that analyte. Ideally, a spectrometer makes measurements either by scanning a spectrum (point by point) or by simultaneous monitoring several positions in a spectrum; the quantity that is measured is a function of radiant power.
Specifically, over all the other analytical methods, the spectroscopic techniques possess the following advantages:
1. These techniques are less time consuming and much more rapid.
2. They require a very small amount (at mg and mg levels) of the compound and even this amount can be recovered at the end of evaluation in many cases.
3. The structural information received from the spectroscopic analysis is much more accurate and reliable.
4. They are much more selective and sensitive and are extremely valuable in the analysis of highly complex mixtures and in the detection of even trace amounts of impurities.
5. Controlled Analysis can be performed on a computer, and therefore, continuous operation is possible which is often required in industrial applications.
A wide array of different spectroscopic techniques can be applied in virtually every domain of scientific research – from environmental analysis, biomedical sciences and material science to space exploration endeavors. In other words, any application that deals with chemical substances or materials can use this technique: Spectro-chemical methods have provided perhaps the most widely used tools for the elucidation of molecular structure as well as the quantitative and qualitative determination of both inorganic and organic compounds. For example, in biochemistry; it is used to determine enzyme-catalyzed reactions. In clinical applications, it is used to examine blood or tissues for clinical diagnosis.

A chemist routinely employs spectroscopic techniques for determination of molecular structure (e.g., NMR Spectroscopy), molecular weight, molecular formula and decomposition to simpler compounds or conversion into a derivative (MS Spectroscopy) and presence or absence of certain functional groups (IR Spectroscopy). Also, there are tremendous efforts in improving (e.g., instruments’ resolution, detection limits, etc) and expanding this branch of the analytical method for quantitative analysis in various fields such as chemistry, physics, biochemistry, material and chemical engineering, clinical applications and industrial applications.
This book aims to cover chemical analysis and material characterization with this technique, this chapter aims to build a foundation for the book by providing properties of EM and the processes which arise after interaction with matter.

Classification of spectroscopic techniques

Methods of spectroscopy can be classified according to the type of analytes they are being analyzed or type of light that they employ. For stance, on the basis of type of analyte (elemental or molecular), it is divided into the following two heads:
1. Atomic spectroscopy: This kind of spectroscopy is concerned with the interaction of electromagnetic radiation with atoms which are commonly in their lowest energy state, called the ground state.
2. Molecular spectroscopy: This spectroscopy deals with the interaction of electromagnetic radiation with molecules. The interaction process results in a transition between rotational and vibrational energy levels in addition to electronic transitions. The spectra of molecules are much more complicated than those of atoms, as molecules undergo rotations and vibrations besides electronic transitions. Molecular spectroscopy is of great importance nowadays due to the fact that the number of molecules is extremely large as compared with free atoms.
Alternatively, the spectroscopic techniques are also classified according to the type of radiation they employ and the way in which this radiation interacts with matter. These methods include those that use from radio wave to Gamma-rays and causes to change from nuclear spin to change in nuclear configuration (see Table 1.1). On this basis, spectroscopic methods are listed below.
(i)Gamma-ray emission spectroscopy: Uses light over the Gamma-ray range (0.005e1.4 AËš)of electromagnetic radiation spectrum
(ii)X-Ray absorption/emission/fluorescence/diffraction spectroscopy: Uses light over the X-ray range (0.1e100 A˚)
(iii)Vacuum ultraviolet absorption spectroscopy: Uses light over the vacuum ultraviolet range of (10e180 nm)
(iv)Ultravioletevisible absorption/emission/fluorescence spectroscopy: Uses light over the ultraviolet range (180e400 nm) and visible range (400e780 nm).
(v)Infra-red absorption spectrophotometry: Uses light over the infrared range (0.78e300 mm).
(vi)FT-IR spectroscopy: (0.78e300 mm)
(vii)Raman scattering spectroscopy: (0.78e300 mm)
(viii)Microwave absorption spectroscopy: Uses light over the infrared range of (0.75e375 mm)
(ix)Electron spin resonance spectroscopy: Uses the light of (3 cm)
(x)Nuclear magnetic resonance spectroscopy: Uses light over the infrared range (0.6e10 m)