Post on 08-Apr-2018
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Detection SystemsDetection Systems
y Electron Capture Detectors
one of the most widely used detectors
for environmental samples because this
detector selectively responds to
halogen-containing organic compounds,
such as pesticides and polychlorinated
biphenyls.
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Detection SystemsDetection Systems
y Electron Capture Detectors
the sample eluate from a column is
passed over a radioactive -emitter,
usually nickel-63.
highly sensitive and have the advantage
of not altering the sample significantly.
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Electron Capture DetectorElectron Capture Detector
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Electron Capture DetectorElectron Capture Detector
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Detection SystemsDetection Systems
y Mass Spectrometry
one of the most powerful detectors in
gas chromatography.
measures the mass-to-charge ratio
(m/z) of ions that have been produced
from the sample.
Combination of gas chromatographyand mass spectrometry is called GC/MS.
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GC/MS DeviceGC/MS Device
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Block diagram of a mass spectrometer
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Ionization
source
Inlet
Analyzer
(Vacuum System)
Ion Detector
Data System
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Detection Systems
Mass Spectrometry
Inlet Systems
Samples put must be pure because thefragmentation occurs causes the mass
spectrum of mixtures to be very difficult
to interpret.
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Detection Systems
Mass Spectrometry
Inlet Systems
Gas chromatography is an ideal way tointroduce mixtures because components
are separated from the mixture prior to
introduction to mass spectrometer.
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Detection SystemsDetection Systems
y Mass Spectrometry
Ionization Sources
x converts gas phase sample molecules into
ions
x can convert gas phase sample molecules
into ions (or, in the case of electrospray
ionization, move ions that exist in solutioninto the gas phase)
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Ionization Sources for Molecular Mass Spectrometry
BASIC
TYPE
NAME &
ACRONYM
METHOD
OFIONIZATION
TYPE OF
SPECTRA
Gas
Phase
Electron
Impact (EI)
Energetic
electrons
Fragmentation
patterns
Chemical
Ionization
(CI)
Reagent
gaseous ions
Proton adducts,
few fragments
Desorptio
n
Fast atom
bombardmen
t (FAB)
Energetic
atomic beam
Molecular ions &
fragments
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Ionization Sources for Molecular Mass Spectrometry
(cont.)
BASICTYPE NAME &ACRONYM METHOD OFIONIZATION TYPE OFSPECTRA
Desorption
(cont.)
Matrix-
assisted laser
desorption/ioni
zation
(MALDI)
High-energy
photons
Molecular
ions, multiply
charged ions
Electrosprayionization
(ESI)
Electric fieldproduces
charged
spray, w/c
desolvates
Multiplycharged
molecular
ions
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Detection SystemsDetection Systems
y Mass Spectrometry
Analyzers
x separates the ions according to their m/z
values.
x sorts the ions by their masses by applying
electromagnetic fields
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Common Mass Analyzers for Mass Spectrometry
BASIC TYPE ANALYSIS PRINCIPLE
MagneticSector
Deflection of ions in a magnetic field.
Double
focusing
Electrostatic focusing followed by magnetic
field deflection.
Quadrupole Ion motion in dc and radio-frequency fields.
Ion Trap Storage of ions in space defined by ring
and end cap electrodes.
Ion-cyclotron
resonance
Trapping of ions in cubic cell under
influence of trapping voltage and magnetic
field.
Time-of-flight Equal kinetic energy ions enter drift tube. 14
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Other Types of DetectorsOther Types of Detectors
y Thermionic Detector nitrogen and phosphorus-containing
compounds produced increase currents in a
flame in which an alkali metal salt isvaporized .
Widely used for organophosphorus
pesticides and pharmaceutical compounds.
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Other Types of DetectorsOther Types of Detectors
y Electrolytic-conductivity or Hall detector compounds containing halogens, sulfur or
nitrogen are mixed with a reaction gas in a
small reactor tube the change in conductivity in the active
compound present is measured.
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ElectrolyticElectrolytic--Conductivity DetectorConductivity Detector
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Other Types of DetectorsOther Types of Detectors
y Photoionization Detector
molecules are photoionized by ultraviolet
radiation the ions and electrons produced are then
collected with a pair of biased electrodes,
and the resulting current is measured
Used for aromatic and other molecules that
are easily photoionized.
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PhotoionizationPhotoionization DetectorDetector
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GASGAS--SOLID CHROMATOGRAPHYSOLID CHROMATOGRAPHY
y Based on adsorption of gaseous
substances on solid surfaces.
y Useful for the separation of species that
are not retained by gas-liquid columns.
y Performed with both packed and open
tubular columns (also called porous-layer
open tubular columns or PLOT columns).
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