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Detectors - Coggle Diagram
Detectors
DAD
(
Diode Array Detectors
)
Mechanism:
Two light sources
(Tungsten lamp + Deuterium lamp) are used to produce light across a broad spectrum of wavelengths in the range UV-visible light
The emitted light passes through the
liquid sample
, which moves through a flow cell. The sample contains different analytes, each absorbing at certain wavelengths depending on their chemical properties
The light which is not absorbed by the sample reaches a
diffraction grating
, where it is split into different colors
Diffracted light reaches the
diode array
. In the array, each diode is sensitive to a specific wavelength of light. This array comprehensively
covers a broad range of wavelengths
, from UV to visible
The
absorption spectrum
generated from the data collected by the diode array is used to identify the
components of the sample
Produce a
UV spectrum
which shows the absorption in a wide range of wavelengths, from 200nm (UV) to 700nm (visible) simultaneously
Useful to detect
organic compounds
with
conjugated double bonds
, because these are the kind of molecules that are able to absorb light in the range UV-visible
Measure the
absorbance of UV-Vis light
, across a wide range of wavelengths, for the molecules within a sample
FLD
(
Fluorescence detectors
)
Measure the
emission of light
by molecules after excitation with light at specific wavelengths
Detect molecules which are capable of emitting fluorescence upon excitation
They are
not universal detectors
, but can only detect compounds with specific chemical characteristics
RID
(
Refractive Index Detectors
)
Measure the
change in the refractive index
(RI) associated with the presence of an analyte in a solvent
Mechanism:
A beam of light is emitted from a source of light
The light first crosses a reference cell, which is filled only with the solvent
The light then crosses a sample cell, where the sample is flowing. Here, the beam will be deflected compared to the reference cell
The output of the RID corresponds to this change in the RI
Universal detector
(= can be used to measure any kind of analyte)
Disadvantages:
Low sensitivity
Not compatible with solvent gradients
Doesn't provide any structural information
ELSD
(
Evaporative Light Scattering Detector
)
Mechanism:
A liquid sample from LC is sprayed into an heated chamber
The solvent evaporates, leaving dry particles of the analyte
A laser beam hits the particles
A detector measures scattered light from the particles
Measures the
light scattering
which occurs due to the formation of analyte particles after solvent evaporation
Universal detector
Detects all the analytes which are less volatile than the solvent
Useful for
non-volatile
or
semi-volatile
compounds
High sensitivity
Disadvantages:
Does not provide any structural information
MS
(
Mass Spectrometry
)
Almost universal
Provides structural information
High sensitivity
