Spectrometrists Prefer Purity

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Spectrometrists Prefer Purity
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Process GC
6min
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Process GC Information

• Retention time ? Identification
• Intensity ? Abundance

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Process GC Caveats

• Retention time ? Identification (not unique)
• Intensity ? Abundance (Interferences)

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(Process) GC/MS
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Mass spectrum a compounds fingerprint
of acetone
J.T. Watson, Introduction to Mass Spectrometry,
Raven New York, 1986.
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Electrospray Mass Spectrometry
Kebarle and Tang, Anal. Chem.1993, 65, 972A.
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J.T. Watson, Introduction to Mass Spectrometry,
Raven New York, 1986.
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Deconvolution Without Separation
J.T. Watson, Introduction to Mass Spectrometry,
Raven New York, 1986.
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Process GC vs Process MS

• Separation based on differences in solubility.
• 20 minutes for 8-10 compounds.
• Long instrument dead bands.

• Separation based on molecular weight and
  fingerprint.
• Up to 40 compounds or 64 masses in
• Real time. Virtually no instrument dead bands.

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Process Mass Spectrometry

• Well suited to processes monitored by
  chromatographs (GC volatiles LC
  nonvolatiles via evolving electrospray
  technology)
• Faster than chromatography (seconds per analysis)
  with good accuracy and precision
• More information than gc
• Easy to multiplex
• Robust? (Much better than in the past!)

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Methanol
Benzene
100
100
80
80
Relative Intensity (A.U.)
60
60
Relative Intensity (A.U.)
40
40
20
20
0
0
10
20
30
40
50
60
70
80
10
20
30
40
50
60
70
80
m/z
m/z
Methanol/Benzene
100
80
60
Relative Intensity (A.U.)
40
20
0
10
20
30
40
50
60
70
80
m/z
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Process MS Typical ExampleEthylene Oxide
streamMeans for 100 samples

• Nitrogen 53.43 0.0502
• Ethylene Oxide 2.51 0.0059
• Argon 0.37 0.0010
• Methane 0.11 0.0041
• Ethylene Chloride 0.03 0.02 ppm
• Ethane 0.35 0.0029
• CO2 5.80 0.0124
• Ethylene 29.47 0.0339
• O2 7.89 0.0125
• Methyl Chloride 1.25 0.02 ppm

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Butene Isomers
1-Butene
Isobutene
cis-2-Butene
trans-2-Butene
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Mass Spectra of Butene Isomers
1-Butene
Isobutene
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1-Butene in Isobutene
Using all 19 m/zs
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Mass Spectra of Butene Stereoisomers
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All Four Butenes (Non-optimum parameterization)
1
0.8
r2 0.033
0.6
Calculated mole fraction
0.4
0.2
0
0
0.2
0.4
0.6
0.8
1
Actual mole fraction
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Simultaneous AnalysisAll Four
Butenes(Optimum parameterization)
r2 0.985 0.002
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A multi-component gas stream with a pair of C4
isomers

• Methane (CH4)
• Ethane (C2H6)
• Propane (C3H8)
• Propylene (C3H6)
• 1-Butene (C4H8)
• Isobutylene (C4H8)

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Six Component Stream
100
r20.9983
80
60
Calculated Concentration ()
40
20
0
0
20
40
60
80
100
Actual Concentration ()
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Conclusions Process MS

• Rapid simultaneous analysis - even of isomers -
  with good accuracy and precision.
• Parameterization is critical.
• Reliability has proven to be good.
• Liquids are feasible, but more challenging.
• Electrospray offers high-mass capabilities.
• Widely used for monitoring headspace (e.g.,
  health monitoring in a fermentation reactor).