Spectrophotometry

Question 1

• Measurements based on light and other forms of electromagnetic radiation
• Provided the most widely used tools for the elucidation of modern atomic theory

Answer 1

Spectrochemical Methods

Question 2

is any analytical method that uses light for measurement of chemical concentrations

Answer 2

Spectrophotometry

Question 3

• was originally the study of the interaction between radiation and matter as a function of wavelength (λ)
• historically, referred to the use of visible light dispersed according to its wavelength, e.g. by a prism

Answer 3

Spectroscopy

Question 4

• dispersion of light as it travels through a triangular prism

Answer 4

Spectroscopy

Question 5

s the distance between crests of a wave (m)

Answer 5

wavelength

Question 6

is the number of oscillations per second (Hz)

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frequency

Question 7

• is an empirical relationship that relates the absorption of light to the properties of the material through which the light is travelling.

Answer 7

Beer–Lambert law

Question 8

states that there is a logarithmic dependence between the transmission (or transmissivity), T, of light through a substance and the product of the absorption coefficient of the substance, α, and the distance the light travels through the
material

Answer 8

Beer-Lambert Law

Question 9

is the fraction of incident light at a specified wavelength that passes through a sample

Answer 9

Transmittance

Question 10

is a unitless measure of the transmittance of an optical element for a given length at a given wavelength

Answer 10

Optical density

Question 11

• The type of spectroscopy depends on the physical quantity measured.
• Normally, the quantity that is measured is an intensity, either of energy absorbed or produced

Answer 11

Classification of Spectroscopy

Question 12

• involves interactions of matter with electromagnetic radiation, such as light.

Answer 12

Electromagnetic spectroscopy

Question 13

Electromagnetic spectroscopy can be classified into:

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– Emission spectroscopy
– Absorption spectroscopy
– Scattering spectroscopy

Question 14

• is the study of electromagnetic radiation spectra given off by atoms or molecules that undergo a transition to a lower energy level.
• Such a process is called fluorescence or, under certain conditions, phosphorescence.
• Generally, deals with visible light and shorter wavelengths, since fluorescence is less likely to happen with long wavelengths

Answer 14

Emission spectroscopy

Question 15

Emission Spectroscopy
* Examples:

Answer 15

– Fluorescence spectroscopy or fluorometry or spectrofluorometry
– Flame emission spectroscopy
– X-ray fluorescence spectroscopy
– Stellar spectroscopy

Question 16

• is the study of electromagnetic radiation spectra absorbed by atoms or molecules that change energy levels; the atoms usually positioned between a radiation source and the observer.
• uses the range of the electromagnetic spectra in which a substance absorbs
• Often, it is used as an analytical technique; specific chemical compounds have a specific absorption spectrum that acts as a fingerprint.

Answer 16

Absorption spectroscopy

Question 17

can be used to determine the concentration of chemical
compounds in samples

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Absorption spectroscopy

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absorption of infrared radiation,

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Vibrational spectroscopy

Question 19

is a technique for determining the concentration of a particular metal element in a sample

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Atomic absorption

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absorption of ultraviolet and visible light

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UV/visible spectroscopy

Question 21

Measures the absorption of gamma rays by atoms bound in a solid as a function of gamma-ray energy. This is not an analytical technique; it is a means to understand certain microscopic processes in matter.

Answer 21

Mossbauer spectroscopy

Question 22

• It relies therefore heavily on Beer-Lambert law
• the electrons of the atoms in the atomizer can be promoted to higher orbitals for an instant by absorbing a set quantity of energy (i.e. light of a given wavelength).
• This amount of energy (or wavelength) is specific to a particular electron transition in a particular element, and in general, each wavelength corresponds to only one element.
• This gives the technique its elemental selectivity

Answer 22

Atomic Absorption Spectroscopy

Question 23

As the quantity of energy (the power) put into the flame is known, and the quantity remaining at the other side (at the
detector) can be measured, it is possible, from Beer-Lambert law, to calculate how many of these transitions took place, and
thus get a signal that is proportional to the concentration of the element being measured

Answer 23

Atomic Absorption Spectroscopy

Question 24

is the subset of spectroscopy that deals with the infrared region of the electromagnetic spectrum

Answer 24

IR spectroscopy

Question 25

* is widely used in both research and industry as a simple and reliable technique for measurement, quality control and dynamic measurement. * It is of special use in forensic analysis in both criminal and civil cases, enabling identification of polymer degradation for example. * It is perhaps the most widely used method of applied spectroscopy

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Infrared spectroscopy

Question 26

* The beams are both reflected back towards a detector, however first they pass through a splitter which quickly alternates which of the two beams enters the detector. * The two signals are then compared and a printout is obtained

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Infrared Spectroscopy

Question 27

– This prevents fluctuations in the output of the source affecting the data – This allows the effects of the solvent to be cancelled out (the reference is usually a pure form of the solvent the sample is in)

Answer 27

Infrared Spectroscopy

Question 28

* measures the amount of light that a substance scatters at certain wavelengths, incident angles, and polarization angles.

Answer 28

Scattering spectroscopy

Question 29

* is a spectroscopic technique used in condensed matter physics and chemistry to study vibrational, rotational, and other low-frequency modes in a system. * It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range

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Raman spectroscopy

Question 30

* involves interactions with electron beams. * Auger spectroscopy involves inducing the Auger effect with an electron beam. In this case the measurement typically involves the kinetic energy of the electron as variable.

Answer 30

Electron spectroscopy

Question 31

* involves the interaction of charged species with magnetic and/or electric fields, giving rise to a mass spectrum. * is an analytical technique for the determination of the elemental composition of a sample or molecule. * It is also used for elucidating the chemical structures of molecules, such as peptides and other chemical compounds.

Answer 31

Mass Spectrometry (MS)

Question 32

* The technique has both qualitative and quantitative uses. * These include identifying unknown compounds, determining the isotopic composition of elements in a molecule, and determining the structure of a compound by observing its fragmentation.

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Mass Spectrometry

Question 33

involves the frequency of sound.

Answer 33

Acoustic spectroscopy

Question 34

involves the frequency of an external electrical field

Answer 34

Dielectric spectroscopy

Question 35

involves the frequency of an external mechanical stress, e.g. a torsion applied to a piece of material

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Mechanical spectroscopy

Question 36

* is the quantifiable study of electromagnetic spectra. * It is more specific than the general term electromagnetic spectroscopy in that deals with visible light, near-ultraviolet, and near-infrared

Answer 36

Spectrophotometry

Question 37

is a photometer (a device for measuring light intensity) that can measure intensity as a function of the color, or more specifically, the wavelength

Answer 37

Spectrophotometry