Spectrophotometry Flashcards
- Measurements based on light and other forms of electromagnetic radiation
- Provided the most widely used tools for the elucidation of modern atomic theory
Spectrochemical Methods
is any analytical method that uses light for measurement of chemical concentrations
Spectrophotometry
- 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
Spectroscopy
- dispersion of light as it travels through a triangular prism
Spectroscopy
s the distance between crests of a wave (m)
wavelength
is the number of oscillations per second (Hz)
frequency
- is an empirical relationship that relates the absorption of light to the properties of the material through which the light is travelling.
Beer–Lambert law
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
Beer-Lambert Law
is the fraction of incident light at a specified wavelength that passes through a sample
Transmittance
is a unitless measure of the transmittance of an optical element for a given length at a given wavelength
Optical density
- 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
Classification of Spectroscopy
- involves interactions of matter with electromagnetic radiation, such as light.
Electromagnetic spectroscopy
Electromagnetic spectroscopy can be classified into:
– Emission spectroscopy
– Absorption spectroscopy
– Scattering spectroscopy
- 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
Emission spectroscopy
Emission Spectroscopy
* Examples:
– Fluorescence spectroscopy or fluorometry or spectrofluorometry
– Flame emission spectroscopy
– X-ray fluorescence spectroscopy
– Stellar spectroscopy
- 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.
Absorption spectroscopy
can be used to determine the concentration of chemical
compounds in samples
Absorption spectroscopy
absorption of infrared radiation,
Vibrational spectroscopy
is a technique for determining the concentration of a particular metal element in a sample
Atomic absorption
absorption of ultraviolet and visible light
UV/visible spectroscopy
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.
Mossbauer spectroscopy
- 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
Atomic Absorption Spectroscopy
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
Atomic Absorption Spectroscopy
is the subset of spectroscopy that deals with the infrared region of the electromagnetic spectrum
IR spectroscopy
- 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
Infrared spectroscopy
- 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
Infrared Spectroscopy
– 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)
Infrared Spectroscopy
- measures the amount of light that a substance scatters at certain wavelengths, incident angles, and polarization angles.
Scattering spectroscopy
- 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
Raman spectroscopy
- 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.
Electron spectroscopy
- 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.
Mass Spectrometry (MS)
- 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.
Mass Spectrometry
involves the frequency of sound.
Acoustic spectroscopy
involves the frequency of an external electrical field
Dielectric spectroscopy
involves the frequency of an external mechanical stress, e.g. a torsion applied to a piece of material
Mechanical spectroscopy
- 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
Spectrophotometry
is a photometer (a device for measuring light intensity) that
can measure intensity as a function of the color, or more specifically, the wavelength
Spectrophotometry
