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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5647_Библиотеки_им_академика_М_И_Перельмана.pdf
280 6 Comprehensive Insights into Atomic Absorption Spectroscopy
C. Low viscosity
D. Sample aspiration rate
Answer: A
19. What is the primary application of AAS in food and beverage analysis?
A. Identifying ore deposits
B. Environmental monitoring
C. Monitoring food safety
D. Assessing water quality
Answer: C
20. Which type of AAS technique uses a graphite furnace to atomize the sample?
A. Flame AAS
B. Hyphenated AAS
C. Graphite furnace AAS
D. High-resolution AAS
Answer: C
21. What does LIBS stand for in the context of AAS?
A. Laser-induced breakdown spectroscopy
B. Laser-induced spectral beams
C. Light intensity breakdown system
D. Low-intensity background spectroscopy
Answer: A
22. What is the primary advantage of using high-resolution AAS?
A. Lower analysis time
B. Improved sensitivity
C. Enhanced nebulization rate
D. Reduced maintenance requirements
Answer: B
23. What is a common physical interference in AAS?
A. Spectral overlap
B. Low vapor pressure
C. High surface tension
D. Light scattering
Answer: B
24. What type of interference in AAS is caused by the presence of ions in the
sample?
A. Chemical interference
B. Spectral interference
C. Background absorption interference
D. Ionization interference
Answer:
D
Suggested Reading 281
25. Which area of the AAS flame is generally the hottest and most suitable for
spectral analysis?
A. Primary combustion zone
B. Interzonal combustion region
C. Secondary combustion zone
D. None of the above
Answer: C
6.17 Short Questions
1. What is the primary purpose of a monochromator in AAS?
2. Why is it essential to create free metal atoms in AAS?
3. How does a hollow cathode lamp (HCL) function in AAS?
4. What is the role of a nebulizer in the AAS instrument?
5. Which part of the flame in AAS is typically used for spectroscopic analysis?
6. What is the function of ionization suppressors in AAS?
7. What is the primary effect of incomplete atomization in AAS?
8. Give an example of a spectral interference in AAS.
9. What are some applications of AAS in pharmaceutical analysis?
10. How can AAS be used in clinical and biological applications?
Suggested Reading
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Blanco MC, Soto-Ferreiro RM. Problems of instrumental analytical chemistry: a hands-on
guide. World Scienti fic Publishing Company; 2017.
Christian GD, Dasgupta PK, Schug KA. Analytical chemistry. Wiley; 2013.
Dedina J. Hydride generation, atomic absorption spectrometry. Chem Anal. 1995:130.
Fernández B, Lobo L, Pereiro R. Atomic absorpton spectrometry | fundamentals, instrumentation
and capabilities. In: Worsfold P, Poole C, Townshend A, Miró M, editors. Encyclopedia of
analytical science. 3rd ed. Oxford: Academic; 2019. p. 137–43.
Hou X, Jones BT. Inductively coupled plasma/optical emission spectrometry. In: Encyclopedia of
analytical chemistry, vol. 2000. Wiley; 2000. p. 9468–85.
Juhászová L, Burhenn S, Sagapova
absorption spectrometry with a dielectric barrier discharge atomizer: method optimization and
evaluation of analytical performance for tin. Spectrochim Acta B At Spectrosc. 2019;158:
105630.
Labmate Online: Atomic absorption spectroscopy. Accessed Oct 2024.
Lackner M. Tunable diode laser absorption spectroscopy (TDLAS) in the process industries–a
review. Rev Chem Eng. 2007;23(2):65–147.
LibreTextsTM: Atomic
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Metcalfe E.
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absorption spectroscopy: a review. Front Phys. 2022;10:853966.
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L, Franzke
spectroscopy. Accessed 10 Nov 2024.
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282 6 Comprehensive Insights into Atomic Absorption Spectroscopy
Miller J, Miller JC. Statistics and chemometrics for analytical chemistry. Pearson Education; 2018.
Resano M, Flórez MR, García-Ruiz E. High-resolution
spectrometry for the simultaneous or sequential monitoring of multiple lines. A critical review
of current possibilities. Spectrochim Acta B At Spectrosc. 2013;88:85–97.
Sudha PC. Pharmaceutical analysis. Pearson Education India; 2012.
Van Loon JA. Analytical atomic absorption spectroscopy: selected methods. Elsevier; 2012.
Wang T. Inductively coupled plasma optical emission spectrometry. In: Ewing’s analytical instru-
mentation handbook. 4th ed. CRC Press; 2019. p. 55–70.
Waters Corporation: Atomic absorption spectroscopy. Accessed 10 Nov 2024.
Watson DG. Pharmaceutical analysis E-book: a textbook for pharmacy students and pharmaceutical
chemists. Elsevier Health Sciences; 2015.
Welz B, Sperling M. Atomic absorption spectrometry. Wiley; 2008.
Welz B,
Borges DL, Lepri FG, Vale MG, Heitmann U. High-resolution continuum source electrothermal atomic absorption spectrometry—an analytical and diagnostic tool for trace analysis.
Spectrochim Acta B At Spectrosc. 2007;62(9):873–83.
continuum source atomic absorption
Comprehensive Insights into Atomic Emission Spectroscopy
Abstract
Atomic emission spectroscopy (AES) is a powerful analytical technique used to
identify and quantify elements in diverse sample types. The core principle of AES
involves exciting the atoms within a sample, leading to the emission of light at
specific wavelengths. This emitted light forms an emission spectrum unique to
each element, enabling precise elemental analysis. AES categorizes emission
spectra into line, band, and continuous spectra based on the nature of emitted
light. Common components of AES include the emission source, monochromator, detector, and readout device. AES finds wide-ranging applications in various
fields, such as clinical diagnostics, environmental analysis, metallurgy, and art
conservation. However, spectral and chemical interferences can pose challenges
in AES, necessitating strategies to overcome them. Despite these challenges, AES
remains a fundamental tool for elemental analysis, offering insights into the
composition of matter in diverse scientific and industrial applications.
7
Keywords
Atomic emission spectroscopy · Spectral interferences · Detection technologies ·
Calibration methods · Portable AES devices · Hyphenated techniques
7.1 Introduction
Atomic emission spectroscop y (AES) is a type of atomic spectroscop y commonly
used to quantify the presence of elements in different samples. In this technique, the
atoms of the analyte are excited and raised to higher energy levels by providing an
adequate amount of energy, typically in the form of heat. Subsequently, these
excited atoms return to lower energy levels, emitting light energy in the process
283
284 7 Comprehensive Insights into Atomic Emission Spectroscopy
Fig. 7.1 Energy level diagram for atomic and ionic emission. This figure represents the excitation
and emission processes occurring in atomic and ionic systems. On the left side of the diagram,
various excitation paths (labeled a, b, c, and d) are shown. These represent how atoms or ions
absorb energy and transition from the ground state to different excited states. Energy is absorbed,
causing the system to move to higher energy levels. On the right side, the emission processes are
displayed. As the atoms or ions return to lower energy states, they release the absorbed energy in the
form of electromagnetic radiation, shown as wavy lines with associated wavelengths (λ₁, λ₂, λ₃, λ₄).
The atomic emission processes are indicated by transitions between excited atomic states and the
ground state, resulting in the emission of photons at wavelengths λ₁, λ₂, and λ₃, corresponding to
transitions f, g, and h, respectively. In the ionic emission, the ion excited state transitions directly to
the ionic ground state, emitting a photon with a specific wavelength, λ ₄ , associated with the
transition labeled e. The diagram effectively captures the energy differences between various states
and how these differences are manifested in distinct emission lines, contributing to the overall
atomic and ionic spectra
(Fig. 7.1). The emitted energy waves are then directed through monochromators or
filters before being detected by photomultiplier tubes.
7.2 Principle
The principle of AES is based on the excitation and subsequent emission of light by
atoms when they transition from higher energy states to lower energy states. In AES,
the sample is exposed to a high-energy thermal environment, leading to the generation of excited states in atoms or ions, which subsequently emit light in the form of
photons. The emitted light contains specific wavelengths that are characteristic of
each element within the sample. Thus, the analysis of this emission spectrum, which
consists of emission lines from the excited species, provides a quantitative measure
of the analyte’s concentration in the sample. The intensity of emission is directly
proportional to the number of atoms or ions present. Each element possesses a
unique set of energy levels, resulting in a distinct set of wavelengths at which energy
is released. Consequently, these wavelengths serve as distinctive identifiers for each
element found in the sample.
7.3 Types of Emission Spectra Used in AES 285
7.3 Types of Emission Spectra Used in AES
When a light beam is passed through a prism or grating, it is dispersed into its
individual components, creating a range of colors. This collection of colors is
referred to as a spectrum. When an analyte is heated to a high temperature using
an electric or thermal method, it emits light. The light emitted by the analyte is then
subjected to analysis using a spectroscope, and the resulting spectrum is known as an
emission spectrum (Fig.
7.2). Emission spectra in AES play a crucial role in
identifying and quantifying elements in a sample. These spectra are categorized
into several types based on the nature of the emitted light. The following sections
provide the main types of emission spectra in AES.
7.3.1 Line Spectra
Line spectra are characterized by distinct, sharp emission lines at specific
wavelengths. These lines correspond to transitions between discrete energy levels
within an atom.
• Example: The emission spectrum of hydrogen is a classic example of line spectra.
When hydrogen gas is excited (e.g., by applying an electric discharge), it emits
light at specific wavelengths corresponding to the transitions of electrons between
energy levels. The most famous series is the Balmer series, which includes visible
lines such as:
– H-alpha (656.3 nm)
– H-beta (486.1 nm)
– H-gamma (434.0 nm)
Fig. 7.2 Schematic representation of light dispersion using a grating and detection system. This
figure illustrates the setup of a light dispersion system involving a grating and mirrors to analyze the
spectrum of a light source. Light from the source is directed toward a grating, which disperses the
light into its constituent wavelengths. The dispersed light is then reflected by a series of mirrors,
causing the various wavelengths (represented by different colors) to be spatially separated. These
separated light components are directed toward a detector, which records the intensity of each
wavelength. The grating’s rotation allows for the selection and adjustment of specific wavelengths
to be detected, enabling spectral analysis
286 7 Comprehensive Insights into Atomic Emission Spectroscopy
• Applications: Line spectra are commonly used in spectroscopy to identify
elements in various fields, including astrophysics (e.g., identifying elements in
stars) and analytical chemistry.
7.3.1.1 Formation of Line Spectra
Line spectra are produced when electrons in an atom are excited to higher energy
levels and then return to lower levels, releasing energy in the form of light. The
wavelengths of the emitted light are determined by the diff erence between the energy
levels involved in these transitions.
7.3.1.2 Unique Spectral Fingerprint of Each Element
Each element has a unique set of energy levels, resulting in light emission at specific
wavelengths. This pattern of well-defined emission lines, often referred to as the
element’s “spectral fingerprint,” allows for precise identification of elements in a
sample.
7.3.1.3 Importance for Elemental Identification
The presence of unique emission lines makes line spectra a powerful tool for
identifying elements. The position of each line corresponds to a particular element,
making it possible to detect and differentiate between multiple elements within a
sample.
7.3.1.4 Correlation with Element Concentration
The intensity of each emission line is directly related to the concentration of the
corresponding element in the sample. This makes line spectra valuable for both
qualitative and quantitative analysis in atomic emission spectroscopy.
7.3.1.5 Observing Line Spectra in Practice
Line spectra are typically observed in gaseous or vaporized samples, where isolated
atoms emit sharp lines without interference. Spectrometers and detectors are used to
capture and analyze these emission lines, providing detailed information ab out the
sample’s composition, elemental abundance, and atomic structure.
7.3.2 Band Spectra
Band spectra consist of broad, continuous bands of light emission, unlike the sharp,
discrete lines seen in line spectra. These spectra result from the complex inte ractions
of atoms within molecules or compounds.
• Example: The emission
to transitions involving both rotational and vibrational levels. The bands are often
observed in the ultraviolet and visible regions, with bands such as the Lyman and
Werner bands.
spectrum of molecular hydrogen shows band spectra due
7.3 Types of Emission Spectra Used in AES 287
• Applications: Band spectra are useful in studying molecular compositions, chem-
ical bonding, and molecular interactions. They are frequently employed in fields
such as environmental science and atmospheric studies.
7.3.2.1 Formation of Band Spectra
Band spectra occur when molecular species or complex compounds undergo energy
transitions across a wide range of energy levels. The numerous possible transitions in
molecules lead to a continuous spread of emitted wavelengths, forming broad bands
rather than distinct lines.
7.3.2.2 Common Observations in Molecular Species
Band spectra are typically observed in molecular species or complex compounds
rather than isolated atoms. The molecular vibrations, rotations, and electron
transitions in these species contribute to the creation of broad emission bands.
7.3.2.3 Application in Molecular and Compound Analysis
While band spectra are less precise for quantitative analysis of individual elements
due to the lack of sharp, distinct lines, they can provide valuable information about
the molecular composition or structural features of the compo unds present in the
sample. They are particularly useful in studying the molecular environment and
chemical bonding.
7.3.2.4 Limitations for Quantitative Elemental Analysis
Band spectra are not as suitable for detailed quantitative analysis of individual
elements because the broad emission features make it difficult to isolate specific
elemental signatures. However, they remain important for understanding the overall
molecular makeup of complex samples.
7.3.3 Continuous Spectra
Continuous spectra do not display distinct lines or bands. Instead, they cover a
broad, uninterrupted range of wavelengths, resulting in a smooth emission across the
spectrum.
• Example: An ideal blackbody radiator emits a continuous spectrum when heated.
For instance, when an incandescent light bulb is turned on, it emits a continuous
spectrum of light, including all visible colors. The spectrum is characterized by a
peak wavelength that shifts based on the temperature of the filament.
• Applications: Continuous
and are used in various applications, including temperature measurements and
studying the emission properties of materials.
spectra are crucial for understanding thermal radiation
288 7 Comprehensive Insights into Atomic Emission Spectroscopy
7.3.3.1 Formation of Continuous Spectra
Continuous spectra typically arise from a hot, glowing solid, liquid, or dense gas,
where the thermal energy excites a large number of atoms or molecules. This leads to
the emission of light over a wide range of wavelengths, rather than at specific, welldefined points.
7.3.3.2 Common Sources of Continuous Spectra
Continuous spectra are most often observed in high-temperature sources, such as the
emission from a heated solid or an incandescent light bulb. These spectra reflect the
overall energy distribution of the emitting material rather than specific atomic or
molecular transitions.
7.3.3.3 Role in AES
While continuous spectra are less frequently encountered in AES compared to line
and band spectra, they still play an important role. They are particularly relevant for
understanding the broad emission profiles of certain high-temperature sources or
materials, providing insight into the general thermal emission of a sample.
7.3.3.4 Limitations in Elemental Analysis
Continuous spectra are not useful for precise elemental ident ification because they
lack the distinct features that correspond to specific elements. However , they provide
valuable context in the analysis of emission sources and help to differentiate between
atomic and molecular emissions.
7.3.4 Combination Spectra
In certain cases, a single emission spectrum may display a combination of line, band,
and continuous spect ra. This occurs when the sample consists of a mixture of
elements, molecular compounds, or sources with varying emission properties.
7.3.4.1 Mixed Emission Sources
When a sample contains both atomic species and molecular compounds, the emission spectrum can exhibit sharp line spectra from individual elements, broad band
spectra from molecules, and continuous spectra from high-temperature sources.
Each of these spectral features reflects the different ways atoms and molecules
emit light under excitation.
7.3.4.2 Interpreting Complex Emission Spectra
In such complex spectra, it is crucial to carefully analyze and differentiate between
the line, band, and continuous components to accurately identify and quantify the
elements and compounds present in the sample. Advanced techniques, such as highresolution spectroscopy, may be required to resolve overlapping spectral features
and provide a clearer picture of the sample’s composition.
7.3 Types of Emission Spectra Used in AES 289
7.3.4.3 Significance in Analytical Applications
The presence of combined spectra is important in real-world applications where
samples are often heterogeneous. Understanding and interpreting these mixed spectra allow for comprehensive analysis of both elemental and molecular content,
providing deeper insights into the sample’s overall composition.
Example:
• Atmospheric emission: An example of combination spectra can be observed in the
analysis of sunlight or starlight passing through Earth’s atmosphere. The light
emitted from the sun is a continuous spectrum, while specific absorption and
emission lines are introduced by atmospheric gases such as oxygen, nitrogen, and
carbon dioxide.
– Continuous spectrum: The sunlight itself emits a continuous spectrum, cover-
ing the entire visible range and beyond.
– Absorption and emission lines: As the sunlight passes through the atmosphere,
certain wavelengths are absorbed by atmospheric gases. When these gases are
excited (e.g., through thermal energy or other processes), they can re-emit
light, producing sharp emission lines superimposed on the continuous background of the solar spectrum. For example, the Fraunhofer lines in the solar
spectrum represent absorption features, while the emission lines of specific
gases can also be observed when analyzing atmospheric emissions.
• Flame emission spectroscopy: In a flame emission spectroscopy setup, when a
complex sample containing both elemental and molecular species is introduced
into a flame, the resulting emission spectrum can be a combination of:
– Line spectra: Sharp lines from elements such as sodium (e.g., the D-lines at
589.0 nm and 589.6 nm).
– Band spectra: Broad bands from molecular species or compounds, such as the
emission bands from metal oxides.
– Continuous spectrum: The background continuum generated by the thermal
energy of the flame itself.
Applications: Combination spectra are valuable in a variety of fields:
• Environmental monitoring: Analyzing pollutants in the atmosphere by observ-
ing combination spectra helps in identifying the presence of multiple gases and
their concentrations.
• Astrophysics: Underst
anding the
composition of celestial bodies and interstellar mediums involves analyzing combination spectra resulting from v arious
elements and compounds present in those environments.
• Material science: Investigat ing materials that contain both elemental and
molecular components can provide insights into their chemical and physical
properties.