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10: Spectroscopic Methods

Last updated

Sep 12, 2021
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- 9.8: Chapter Summary and Key Terms
- 10.1: Overview of Spectroscopy

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An early example of a colorimetric analysis is Nessler’s method for ammonia, which was introduced in 1856. Nessler found that adding an alkaline solution of HgI₂ and KI to a dilute solution of ammonia produced a yellow-to-reddish brown colloid, in which the colloid’s color depended on the concentration of ammonia. By visually comparing the color of a sample to the colors of a series of standards, Nessler was able to determine the concentration of ammonia. Colorimetry, in which a sample absorbs visible light, is one example of a spectroscopic method of analysis. At the end of the nineteenth century, spectroscopy was limited to the absorption, emission, and scattering of visible, ultraviolet, and infrared electromagnetic radiation. Since then, spectroscopy has expanded to include other forms of electromagnetic radiation—such as X-rays, microwaves, and radio waves—and other energetic particles—such as electrons and ions.

10.1: Overview of Spectroscopy
This chapter explores the interaction of electromagnetic radiation with matter, particularly in the context of spectroscopy. It covers the principles of spectroscopy using ultraviolet, visible, and infrared radiation. The chapter explains the wave and particle nature of electromagnetic radiation, highlighting its fundamental properties and explaining how matter absorbs or emits photons.
10.2: Spectroscopy Based on Absorption
The page explains the principles and applications of absorption spectroscopy. It describes how electromagnetic radiation passes through a sample, and selective absorption at certain wavelengths leads to attenuation, essential for identifying various molecular and atomic transitions. The page covers the requirements for an analyte's absorption, mechanisms involved, differences in infrared and UV/Vis spectra, and factors influencing spectral characteristics.
10.3: UV/Vis and IR Spectroscopy
The page discusses the evolution of color matching in spectroscopy, detailing the transition from Nessler's original method to modern photoelectric and infrared methods in the 1930s and 1940s. It then describes different instrument designs for molecular absorption spectroscopy, including filter photometers, single-beam and double-beam spectrophotometers, and diode array spectrometers, highlighting their features and limitations.
10.4: Atomic Absorption Spectroscopy
The page provides an in-depth overview of atomic absorption spectroscopy, detailing its historical development, instrumentation, and methods of analysis. It covers processes such as atomization, including flame and electrothermal atomization, and discusses the advantages and limitations of each method. The page also elaborates on procedures for sample preparation, identifying and correcting interferences, and choosing appropriate wavelengths and slit widths for accurate measurements.
10.5: Emission Spectroscopy
This page discusses the concept of an analyte in an excited state and the processes of relaxation to its lower energy state. It elaborates on how excess energy is released in various ways, including as heat through vibrational relaxation, through photochemical reactions, or as a photon via electromagnetic radiation.
10.6: Photoluminescent Spectroscopy
This page provides an in-depth explanation of photoluminescence, dividing it into two categories: fluorescence and phosphorescence. It describes the processes, mechanisms, and factors influencing both types, including radiative and non-radiative deactivation pathways. The page discusses the technological advancements in fluorescence and phosphorescence spectroscopy, related instrumentation, and depicts their quantitative applications for analyzing inorganic and organic analytes.
10.7: Atomic Emission Spectroscopy
This page discusses atomic emission spectroscopy (AES), a method for analyzing elements by recording the light emitted from excited atoms. The historical development of AES is highlighted, with applications evolving from flame and spark techniques to plasma sources. AES is suitable for multielemental analysis and involves equipment like atomic emission spectrometers using flames or plasmas.
10.8: Spectroscopy Based on Scattering
This page explains the scattering of light, focusing on why the sky appears blue and sunsets look red based on light's wavelength and atmospheric particles. Elastic scattering is discussed, with two types: Rayleigh and large-particle scattering. Turbidimetry and nephelometry, techniques that measure scattered radiation, are compared. The choice between them depends on particle concentration and size. Applications include water clarity and cation/anion determination.
10.9: Problems
The document appears to be focused on various analytical chemistry problems involving spectrophotometry, colorimetry, and molecular absorption techniques in different contexts such as determining concentrations of elements or compounds in different scenarios like solutions, beverages, and solid matrices. The problems cover applications of Beer???s Law, stoichiometry of complex formation, and effects of instrumental limitations.
10.10: Additional Resources
The page provides a comprehensive overview of various experiments in spectroscopy targeted at students, organized into categories such as UV/Vis spectroscopy, IR spectroscopy, atomic absorption and emission, fluorescence and phosphorescence, and signal averaging.
10.11: Chapter Summary and Key Terms
The chapter covers spectrophotometric techniques based on the absorption, emission, or scattering of electromagnetic radiation. It explains how molecules and atoms absorb radiation, causing changes in energy states, and measures such as Beer???s law are used to relate absorbance to concentration. The chapter describes atomic absorption and emission methods, as well as scattering techniques like turbidimetry and nephelometry. Key terms related to spectroscopy methods and processes are included.

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