Medical brain notes 14

  INTRODUCTION Emission spectroscopy  is exclusively related to atoms whereas a number of other spectroscopic   techniques deal with molecules. The fundamental fact of emission spectroscopy is very simple, wherein the atoms present in a sample undergo excitation due to the absorption of either electrical or thermal energy. Subsequently, the radiation emitted by atoms in an excited sample is studied in an elaborated manner both qualitatively and quantitatively. Therefore, emission spectroscopy is considered to be an useful analytical tool for the analysis of :   ( i ) elemental analysis of metals,   ( ii ) identification and quantitative determination of metallic elements,   ( iii ) estimation of metalloids  e.g. , arsenic, silicon, selenium, present is extremely low concentrations, and   ( iv ) analysis of solids, liquids or gases as follows :   solids-as such or evaporated solutions,   liquids-atomized spray, analyzed occasionally, and ...

  THEORY The theoretical aspects of emission spectroscopy may be categorized into the following  four  heads, namely :   ( a )  Spectra :   A beam of light on being passed either through a Nicol’s prism or a grating, is split-up right into its constituent array of colours frequently termed as  spectrum . However, the complete spectrum has a wide range that may be further divided into various regions based on their respective wavelengths (0 to 35,000° A) :   ( i )  Ultraviolet Region :  It embraces radiations of wavelengths between 0 to 4000° A,   ( ii )  Visible Region :  It includes radiations of wavelengths between 4000 to 7300° A, and   ( iii )  Infrared Region :  It has radiations of wavelengths between 7300 and 35,000° A.   ( b )  Classes of Spectra :   There exist, in fact, two major types of spectra commonly termed as  emission   spectra  and the  absorption spectra...

  INSTRUMENTATION The various essential components of a reasonably good emission spectrograph are as follows, namely :   ( i ) Excitation sources,   ( ii ) Electrodes,   ( iii ) Sample Handling,   ( iv ) Monochromators,   ( v ) Detectors, and   ( vi ) Spectrographs.     1. EXCITATION SOURCES   The excitation sources may be sub divided into the following  two  heads, namely :   ( a )  Salient Features of Excitation Sources :  These should fulfil the following procedural require-ments :   ·                Sample should be changed into its vaporised form,   ·                Vaporised form of sample must be dissociated into atoms,   ·                Electrons present in the atoms should be excite...