Term
| advantages of GC in analytical Toxicology |
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Definition
-can inject aqueso mixtures
-sensitive universal & selective detectors
-reproducible
-can be used for a wide range of gases and solvents
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Term
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Definition
-analyte or derivative must be volatile and stable at room temp
- highly polar/ionizable groups have poor performance
-interference from thermally labile compounds
-spetum injection requires frequent maintinence |
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Term
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Definition
Gas supply unit (flow controller)
Injector (housed in injector oven)
Column (in own oven)
detctor (in own oven)
Data processing system |
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Term
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Definition
on column: positioned near spetumand packed with glass wool,analyte injected belowtempofsolvent
off column: liner contains glass wool(samples injected directly into liner) **useful if specimin is not clean (aka glass wool) |
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Term
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Definition
used when working with with WCOT coliummns
-can reduce sample size greatly (1/50)
rest of sample is sent out through the split vent
- smaller sample allows for faster binding and seperation |
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Term
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Definition
Capillary column
Wall Coated Open Tubular columns where thin layer of stationary phase id bonded to wall of a columnwith remaining central portion of the interior column open |
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Term
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Definition
Capillary column
is when a liquid stationary phase is coated onto particles like BaCl microcrystals that are bonded onto the inner surface of the capillary wall. |
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Term
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Definition
When molecules contact surface, they adsorb onto surface
Binding energy varies w/ combination of adsorbate and surface
If surface heated, energy transferred to adsorbed species will cause it to adsorb
Separation carried out by thermal desorption |
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Term
| oCyrofocusing = “purge and trap” of volatile analytes |
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Definition
Necessary if matrix contains water
Specimens trapped as gas flows thru porous polymer trap→ analytes adsorbent to polymer
H2O in sample remains in gas and flows into cold trap
• Removed from syst. by purging with N to cool trap
Adsorbed specimen can be thermally desorbed
o Use: analysis of volatile cmpds. in potable water
Little application in analysis of biological samples |
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Term
| •Thermal-conductivity detection |
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Definition
oRelatively insensitive (1ng on column)
oPoor linear range
oUseful for permanent gases and CO (which are unresponsive to FID, ECD, MS)
oPrinciple: resistance of an electrically heated filament placed in column effluent changes as composition of eluent changes |
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Term
| •Flame-ionization detection |
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Definition
| ionization produced as column effluent passes into Hydrogen/air flame changes as effluent composition changes. Change in ionization is monitored as charge in standing current maintained by applying potential difference b/w flame tip and collector electrode |
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Term
| •Nitrogen-phosphorus detection |
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Definition
oBased on FID, but differs→ contains Rb or Cs-silicate (glass) beat situated in heater coil a little distance from H flame
oIntroduces alkali metal vapor into flame to give selective response to compound containing P or C-N bonds via adjustment of flame gases
oSeparates analyte from most solvents b/c most solvents do not contain CN bond |
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Term
| •Electron Capture Detection |
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Definition
electrons produced from 63Ni source or by plasma discharge are selectively “captured” by certain analytes in column effluent, thus causing decrease in standing current maintained b/w source and collector
DC mode or Pulsed Mode
-very sensitive GC detector
-cannot use at high temperatures |
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Term
| •Pulsed-discharge detection |
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Definition
Pulsed-discharged Helium photoionization (He-PDPID)(detects permanant gases and compounds that do not respond with FID)
-Pulsed-discharged electron capture (PDECD)(no saftey requirements)
-Helium-ionization emission (PDED) |
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Term
| Flame-photometric detection |
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Definition
oExploits chemiluminescence of S or P when heated in flame to give relatively specific detection for substances containing either element
oλmax for emission of excited S2 (emitting species for S) ~ 394nm
Excited HPO shows doublet at 510-526 nm
oInterference filter placed b/w flame and photomultiplier tube determines selectivity (used in specialized areas, like pesticide development) |
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Term
| •Atomic emission detection |
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Definition
oMeasures no. of elements (~15) selectively and simultaneously in GC effluent
oAnalytes eluting from GC column pass into microwave plasma (or discharge) cavity where individual atoms are excited from ground state by heat energy of plasma
oEach element emits light of specific λ when decaying from excited state which can be measured via photodiode array (usually range 170-800nm) |
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Term
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Definition
stationary phase chemically bonded onto inner surface of column
oOuter coating of polyimide protects brittle silica giving mechanical strength and flexibility
oSilica usually coiled and held in metal support (cage)
-Typical dimensions: 0.05-0.53 mm i.d. and 10-50m length
oPolyimide coating imposes upper operating temp. limit of 360°C ( |
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Term
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Definition
oConventional borosilicate glass, stainless steel, or glass-lined stainless steel packed columns
-GSC packings mainly used in analysis of gases and solvents (Stationary phase is active solid ) |
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Term
| PLOT (porous-later open tubular) |
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Definition
•Capillary column
fine (10μm or less) layer of stationary phase particles bonded to internal surface of capillary
•Used for analysis of volatile substances, i.e. permanent gases |
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Term
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Definition
When sample is separated using 2 dissimilar columns, total peak capacity will be produce of individual column peak capacities
For maximum gain in resolution: separation in individual time dimensions should be totally uncorrelated or orthogonal (rarely occurs) |
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