Gas$Chromatography$ - Faculty...

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Gas Chromatography Se$ng Parameters Defini0on of Parameter: Example?

Transcript of Gas$Chromatography$ - Faculty...

Page 1: Gas$Chromatography$ - Faculty Websitesfaculty.sites.uci.edu/chem2l/files/2011/03/B08LECGCParameter.pdf · Analyte$! Organic liquids or!low MP solids.!!(V!=0.01!to!1.0! µL)Only! certain!chemicals!can!be!puton!certain!columns.!!Chemicals!for!

ì  Gas  Chromatography  Se$ng  Parameters  

Defini0on  of  Parameter:  

set  of  physical  proper0es  whose  values  determine  the  characteris0cs  or  behavior  of  something.      Example:  Parameters  of  the  atmosphere  can  be  temperature,  pressure,  and  density.  

         -­‐  Merriam-­‐Webster  Dic=onary  

Example?  

Page 2: Gas$Chromatography$ - Faculty Websitesfaculty.sites.uci.edu/chem2l/files/2011/03/B08LECGCParameter.pdf · Analyte$! Organic liquids or!low MP solids.!!(V!=0.01!to!1.0! µL)Only! certain!chemicals!can!be!puton!certain!columns.!!Chemicals!for!

Comparing  Gas  &  Liquid  Chromatography  

Type  of  Chromatography  

Liquid:    TLC  or  Column  

Gas  

Sta0onary  Phase   powdered  silica     Stainless  steel  column  coated  w/  PDMS  

Mobile  Phase   liquids  -­‐  eluents    (organic  solvents)  

gas    (iden0ty  depends  on  separa0on,  air  for  GChem)  

Force  crea0ng  flow! capillary  ac0on  (TLC)  or  gravity  (column)  

gas  pressure    &  column  temperature  

Page 3: Gas$Chromatography$ - Faculty Websitesfaculty.sites.uci.edu/chem2l/files/2011/03/B08LECGCParameter.pdf · Analyte$! Organic liquids or!low MP solids.!!(V!=0.01!to!1.0! µL)Only! certain!chemicals!can!be!puton!certain!columns.!!Chemicals!for!

1.  Injector  port  for  a  µL  syringe.            2.  Injector  port  heater  to  evaporate  

analyte  chemicals.  3.  Fan  to  create  pressure  for  air  carrier  

gas.    (In  other  GCs,  port  to  connect  carrier  gas.)  

4.  11  m  long  stainless  steel  column  w/  an  internal  diameter  of  0.53  mm.  

5.  Column  Oven:  hea0ng  element  &  circula0ng  fan  

6.  Detector  7.  Recorder  (Computer)  

What  is  a  Gas  Chromatograph?  

Page 4: Gas$Chromatography$ - Faculty Websitesfaculty.sites.uci.edu/chem2l/files/2011/03/B08LECGCParameter.pdf · Analyte$! Organic liquids or!low MP solids.!!(V!=0.01!to!1.0! µL)Only! certain!chemicals!can!be!puton!certain!columns.!!Chemicals!for!

Stationary  Phase  

ì  11  m  column:  stainless  steel  coiled  capillary  tubing  w/  an  interior  coa0ng  of  polydimethylsiloxane  (PDMS)  

ì  Analytes  adsorb  onto  PDMS.  ì  What  is  the  polarity  of  PDMS?  ì  What  kind  of  IM  forces  might  exist  b/w  

PDMS  &  analyte  molecules?  ì  How  would  measuring  contact  angles  

help  us  understand  this?  

 

PDMS  

Page 5: Gas$Chromatography$ - Faculty Websitesfaculty.sites.uci.edu/chem2l/files/2011/03/B08LECGCParameter.pdf · Analyte$! Organic liquids or!low MP solids.!!(V!=0.01!to!1.0! µL)Only! certain!chemicals!can!be!puton!certain!columns.!!Chemicals!for!

Analyte  ì  Organic liquids or  low MP solids.    (V  =  0.01  to  1.0  µL)  Only  

certain  chemicals  can  be  put  on  certain  columns.    Chemicals  for  the  column  used  in  lab:    

 

 

   

ì  Order  of  elu0on  determined  by  vapor pressure –  chemical  w/  highest  VP  is  eluted  1st.    Unless  IM  Forces  cause  strong  adsorp0on  w/  sta0onary  phase.  

Cpd  Family   #  of  Cs   BP  (°C)   Cpd  Family   #  of  Cs   BP  (°C)  

Alcohols   C1-­‐C8   65-­‐195   Esters   C2-­‐C10   30-­‐120  

Aldehydes   C2-­‐C8   20-­‐170   Ethers   C4-­‐C8   35-­‐145  

Aroma0cs   C6-­‐C10   80-­‐165   Ketones     C3-­‐C8   55-­‐175  

Carboxylic  Acids   C1-­‐C4   100-­‐165   Nitriles   C2-­‐C5   80-­‐140  

Page 6: Gas$Chromatography$ - Faculty Websitesfaculty.sites.uci.edu/chem2l/files/2011/03/B08LECGCParameter.pdf · Analyte$! Organic liquids or!low MP solids.!!(V!=0.01!to!1.0! µL)Only! certain!chemicals!can!be!puton!certain!columns.!!Chemicals!for!

Mobile  Phase  

ì  Carrier  Gas…  Air.    Usually  an  inert  gas  like  Ar  or  He.  

ì  What  parameters  control  a  gas?  ì  Carrier  Gas  Pressure  (Flow  Rate):  1-­‐21kPa    ì  Column  Temperature:  30-­‐120  °C  

ì  Reten0on  Time  (tR):  amount  of  0me  analyte  stays  on  column  

ì  Coelu0on:  when  2+  analytes  come  out  together  

ì  Rela=onship  to  parameters:    é  P  or  T,      ê  tR  but  é  coelu0on  

Page 7: Gas$Chromatography$ - Faculty Websitesfaculty.sites.uci.edu/chem2l/files/2011/03/B08LECGCParameter.pdf · Analyte$! Organic liquids or!low MP solids.!!(V!=0.01!to!1.0! µL)Only! certain!chemicals!can!be!puton!certain!columns.!!Chemicals!for!

Pressure…  aka  Flow  Rate  

ì  Carrier  Gas  Pressure  determines  how  quickly  carrier  gas  flows  thru  column.  

ì  For  our  column:                                Flow  Rate  =  0.54  x  P  

ì  High  flow  rate  =      low  reten0on  0me  =  greater  coelu0on      =  bad  separa0on    

Pressure  (kPa)   Flow  Rate(mL/min)  at  45  °C  

2.5   1.4  

5.0   2.7  

7.5   4.1  

10.0   5.4  

12.5   6.8  

15.0   8.1  

17.5   9.5  

20.0   10.8  

Page 8: Gas$Chromatography$ - Faculty Websitesfaculty.sites.uci.edu/chem2l/files/2011/03/B08LECGCParameter.pdf · Analyte$! Organic liquids or!low MP solids.!!(V!=0.01!to!1.0! µL)Only! certain!chemicals!can!be!puton!certain!columns.!!Chemicals!for!

GC  Programming:  P  &  T  

ì  Carrier  Gas  Pressure  (Flow  Rate)  

ì  Injector  Temp  

ì  Start  Temp  

ì  Hold  Time:  length  of  0me  temp  is  held  constant  

ì  Ramp  Rate:  how  quickly  oven  changes  temperature  

ì  Final  Temp  

If  P  or  T  is…  

ì  too  low:  tR  is  long    ì  Analyte  will  not  come  off  the  column  for  a  long  0me.  

ì  too  high:  coelu0on  of  peaks  ì  2+  analytes  have  same  short  tR,  no  separa0on.  

100  50  

Page 9: Gas$Chromatography$ - Faculty Websitesfaculty.sites.uci.edu/chem2l/files/2011/03/B08LECGCParameter.pdf · Analyte$! Organic liquids or!low MP solids.!!(V!=0.01!to!1.0! µL)Only! certain!chemicals!can!be!puton!certain!columns.!!Chemicals!for!

Parameters  of  a  good  Chromatogram  

Bad   Good  

Trial  &  Error  are  used  to  find  the  right  P  &  Ts  to  make  a  good  chromatogram.  

Page 10: Gas$Chromatography$ - Faculty Websitesfaculty.sites.uci.edu/chem2l/files/2011/03/B08LECGCParameter.pdf · Analyte$! Organic liquids or!low MP solids.!!(V!=0.01!to!1.0! µL)Only! certain!chemicals!can!be!puton!certain!columns.!!Chemicals!for!

Injecting  Analyte  into  GC  ì  Wait  un0l  green  LED  

light  is  lit  &  “Ready  for  Injec0on”  appears  

ì  Clean  syringe  by  flushing  w/  acetone  3xs.  ì  Do  not  bend  

needle.    ì  Never  fill  syringe  to  

more  than  50%  of  its  total  volume.      

ì  Do  not  bend  plunger  as  you  push  it  down.  

ì  Load  syringe  w/  analyte  soln  ì  Prerinse  3xs  ì  Fill  syringe  w/  0.5  µL  extra,  holding  

the  syringe  at  eye  level,  depress  the  plunger  to  the  correct  volume,  wipe  excess  on  outside  of  needle  w/  Kimwipe.  

ì  Hold  syringe  w/  one  hand,  pinch  the  needle  to  steady  it  w/  other.  

ì  Insert  needle  into  injec0on  port,  rota0ng  slightly  if  needle  s0cks.    Never  force  the  plunger.  

ì  W/  a  partner,  simultaneously,  depress  syringe  &  select  Collect.    Remove  needle  from  injec0on  port  &  clean  w/  ethanol.  

Page 11: Gas$Chromatography$ - Faculty Websitesfaculty.sites.uci.edu/chem2l/files/2011/03/B08LECGCParameter.pdf · Analyte$! Organic liquids or!low MP solids.!!(V!=0.01!to!1.0! µL)Only! certain!chemicals!can!be!puton!certain!columns.!!Chemicals!for!

Detector  

ì  ChemicapaciMve  sensor:  microcapacitor  coated  w/  a  chemoselec0ve  polymer.      

ì  Analyte  vapor  is  absorbed  as  it  exits  the  column  changing  the  permi$vity  of  the  polymer.  

ì  This  change  leads  to  more  or  less  current  flowing  thru  the  capacitor.  

 

e-­‐   e-­‐   e-­‐   e-­‐  

polymer  

- +

Electrically  conduc0ve  metal  plates  

Current  in  

Current  out