• Gas chromatography = separationGas chromatography = separation• Mass spectrometry = detectionMass spectrometry = detection

CH 103: ATOMIC MASS AND ISOTOPIC ABUNDANCECH 103: ATOMIC MASS AND ISOTOPIC ABUNDANCE

GAS CHROMATOGRAPHY MASS SPECTROMETRYGAS CHROMATOGRAPHY MASS SPECTROMETRY

• A gas chromatograph (GC) separates mixtures of 2 or more A gas chromatograph (GC) separates mixtures of 2 or more different chemicals into pure compounds.different chemicals into pure compounds.

GAS CHROMATOGRAPHYGAS CHROMATOGRAPHY

• The sample is injected into the GC inlet where it is heated The sample is injected into the GC inlet where it is heated and swept onto a chromatographic column by a carrier and swept onto a chromatographic column by a carrier gas.gas.

• The pure compounds in a mixture are separated by The pure compounds in a mixture are separated by interacting with the coating or packing of the column interacting with the coating or packing of the column (stationary phase) and the carrier gas (mobile phase).(stationary phase) and the carrier gas (mobile phase).

• This separation is often improved by programming This separation is often improved by programming changes in column temperature and pressure.changes in column temperature and pressure.

GAS CHROMATOGRAPHYGAS CHROMATOGRAPHY

Splitless Injection AnimationSplitless Injection Animationhttp://www.restek.com/info_animation_splitless.asp http://www.restek.com/info_animation_splitless.asp

• Splitless injections direct the entire sample to the column.Splitless injections direct the entire sample to the column.

2 mL/min septum purge flow + 3 mL/min column flow =2 mL/min septum purge flow + 3 mL/min column flow =5 mL/min total flow 5 mL/min total flow

• Unknowns might be analyzed with a 0.2 μL splitless Unknowns might be analyzed with a 0.2 μL splitless injection to identify minor components.injection to identify minor components.

GAS CHROMATOGRAPHYGAS CHROMATOGRAPHY

Split Injection AnimationSplit Injection Animationhttp://www.restek.com/info_animation_split.asphttp://www.restek.com/info_animation_split.asp

• Split injections direct a fraction of the sample to the Split injections direct a fraction of the sample to the column and the remaining sample vents out of the GC.column and the remaining sample vents out of the GC.

2 mL/min septum purge flow + 1 mL/min column flow + 2 mL/min septum purge flow + 1 mL/min column flow + 100 mL/min split flow = 103 mL/min total flow100 mL/min split flow = 103 mL/min total flow

• Complicated mixtures, such as petroleum, might be Complicated mixtures, such as petroleum, might be analyzed with a 1.0 μL injection using a 1 to 100 split to analyzed with a 1.0 μL injection using a 1 to 100 split to identify major components.identify major components.

GAS CHROMATOGRAPHYGAS CHROMATOGRAPHY

• A mass spectrometer (MS) determines the structure and quantity of A mass spectrometer (MS) determines the structure and quantity of each pure chemical leaving the GC. For example, the mass spectrum each pure chemical leaving the GC. For example, the mass spectrum suggests that this compound is chloromethane (CHsuggests that this compound is chloromethane (CH33Cl). The total Cl). The total

abundance of the peak at m/z = 50 amu suggests that the concentration abundance of the peak at m/z = 50 amu suggests that the concentration of CHof CH33Cl is 150 parts per million (ppm).Cl is 150 parts per million (ppm).

MASS SPECTROMETRYMASS SPECTROMETRY

• The separated compounds leave the GC and enter the ion source in the The separated compounds leave the GC and enter the ion source in the MS where a beam of electrons ionize these molecules. This typically MS where a beam of electrons ionize these molecules. This typically causes the loss of 1 electron from an ionized molecule and produces a causes the loss of 1 electron from an ionized molecule and produces a radical cation called the molecular ion which has the same molecular radical cation called the molecular ion which has the same molecular weight as the original molecule.weight as the original molecule.

MASS SPECTROMETRYMASS SPECTROMETRY

MASS SPECTROMETRYMASS SPECTROMETRY

• The molecular ion usually fragments to produce smaller ions with The molecular ion usually fragments to produce smaller ions with characteristic relative abundances that provide a unique “fingerprint” characteristic relative abundances that provide a unique “fingerprint” for that molecular structure. These positively charged ions are filtered for that molecular structure. These positively charged ions are filtered by the quadrupole of the mass selective detector. Finally, this by the quadrupole of the mass selective detector. Finally, this fingerprint is shown as a mass spectrum.fingerprint is shown as a mass spectrum.

MASS SPECTROMETRYMASS SPECTROMETRY

• Important peaks are Important peaks are 1212CC11HH333737ClCl++. at m/z = 52 amu, . at m/z = 52 amu, 1212CC11HH33

3535ClCl++. at m/z = 50 . at m/z = 50

amu, and amu, and 1212CC11HH33++. at m/z = 15 amu.. at m/z = 15 amu.

MASS SPECTROMETRYMASS SPECTROMETRY

• Important peaks are Important peaks are 1212CC11HH223737ClCl3737ClCl++. at m/z = 88 amu, . at m/z = 88 amu, 1212CC11HH22

3535ClCl3737ClCl++. at . at

m/z = 86 amu, m/z = 86 amu, 1212CC11HH223535ClCl3535ClCl++. at m/z = 84 amu, . at m/z = 84 amu, 1212CC11HH22

3737ClCl++. at m/z = 51 . at m/z = 51

amu, and amu, and 1212CC11HH223535ClCl++. at m/z = 49 amu.. at m/z = 49 amu.

MASS SPECTROMETRYMASS SPECTROMETRY

• Important peaks are Important peaks are 1212CC11HH338181BrBr++. at m/z = 96 amu, . at m/z = 96 amu, 1212CC11HH33

7979BrBr++. at m/z = 94 . at m/z = 94

amu, and amu, and 1212CC11HH33++. at m/z = 15 amu.. at m/z = 15 amu.

MASS SPECTROMETRYMASS SPECTROMETRY

• Important peaks are Important peaks are 1212CC11HH228181BrBr8181BrBr++. at m/z = 176 amu, . at m/z = 176 amu, 1212CC11HH22

7979BrBr8181BrBr++. at . at

m/z = 174 amu, m/z = 174 amu, 1212CC11HH227979BrBr7979BrBr++. at m/z = 172 amu, . at m/z = 172 amu, 1212CC11HH22

8181BrBr++. at m/z = 95 . at m/z = 95

amu, and amu, and 1212CC11HH227979BrBr++. at m/z = 93 amu.. at m/z = 93 amu.

MASS SPECTROMETRYMASS SPECTROMETRY

LIQUID CHROMATOGRAPHY MASS SPECTROMETRYLIQUID CHROMATOGRAPHY MASS SPECTROMETRY

Liquid Chromatography Mass Spectrometry AnimationLiquid Chromatography Mass Spectrometry Animationhttp://www.chem.agilent.com/Scripts/Generic.ASP?lPage=10184&indcol=N&prodcol=Yhttp://www.chem.agilent.com/Scripts/Generic.ASP?lPage=10184&indcol=N&prodcol=Y

• Agilent Technologies. 2006. Agilent. Available: Agilent Technologies. 2006. Agilent. Available: http://www.home.agilent.com/agilent/home.jspx?cc=US&lc=eng&cmpid=4533 [accessed 1 [accessed 1 September 2006].September 2006].

• Agilent Technologies. 2006. 6210 Time-of-Flight LC/MS. Available: Agilent Technologies. 2006. 6210 Time-of-Flight LC/MS. Available: http://www.chem.agilent.com/Scripts/Generic.ASP?lPage=10184&indcol=N&prodcol=Y [accessed 1 September 2006].[accessed 1 September 2006].

• Bull I.D., P. Gates. 2005. Gas Chromatography Mass Spectrometry (GC/MS). Bull I.D., P. Gates. 2005. Gas Chromatography Mass Spectrometry (GC/MS). Available: Available: http://www.bris.ac.uk/nerclsmsf/techniques/gcms.html [accessed 1 [accessed 1 September 2006].September 2006].

• McLafferty, F.W. 1980. Interpretation of Mass Spectra, 3rd ed. Mill Valley, CA: McLafferty, F.W. 1980. Interpretation of Mass Spectra, 3rd ed. Mill Valley, CA: University Science Books.University Science Books.

• National Institute of Standards and Technology. 2006. NIST Chemistry National Institute of Standards and Technology. 2006. NIST Chemistry WebBook. Available: http://webbook.nist.gov/chemistry/ [accessed 1 WebBook. Available: http://webbook.nist.gov/chemistry/ [accessed 1 September 2006].September 2006].

• Restek Corporation. 2006. Split Injection Animation. Available: Restek Corporation. 2006. Split Injection Animation. Available: http://www.restek.com/info_animation_split.asp [accessed 1 September 2006].http://www.restek.com/info_animation_split.asp [accessed 1 September 2006].

• Restek Corporation. 2006. Splitless Injection Animation. Available: Restek Corporation. 2006. Splitless Injection Animation. Available: http://www.restek.com/info_animation_splitless.asp [accessed 1 September http://www.restek.com/info_animation_splitless.asp [accessed 1 September 2006].2006].

SOURCESSOURCES