To give Knowledge about topic

1. INTERFACING GAS
CHROMATOGRAPHY WITH MASS
SPECTROSCOPY
Ms. Harshada. R. Bafna

2. EARLY USE OF MASS SPECTROSCOPY
• Quantitative methods for determination of the components in complex hydrocarbon
mixtures
• Later used for the identification and structural analysis of complex compounds
• Method requires samples that are “clean” or interpretation is confusing
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3. PRINCIPLES OF MEASUREMENTS
• As an identification method:
• When a given molecular species is impacted with an electron beam, a family of
positive particles are produced
• The mass distribution of the particles are characteristic of the parent species
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4. INTERFACING GC WITH SPECTROSCOPIC
METHODS - EARLY
• eluates from column collected as separate fractions after being detected -
composition measured by Mass Spectrometry or IR
• Limitation - small (micromolar) composition of the solute
• procedure still useful for qualitative analysis of multi-component
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5. GC/ MASS SPECTROMETRY
• GC equipment can be directly interfaced with rapid-scan Mass Spectrometers
• The flow rate is usually small enough to feed directly into the ionization
chamber of the Mass Spectrometer
• Packed columns use a jet separator, which removes the carrier gas for the
analyte
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6. GC/ MS
• Increase momentum of heavier analyte molecules so that 50% or more go
into the skimmer
• Lighter helium molecules are deflected by vacuum and pumped away
• Use to identify components present in natural and biological systems
• odor/flavor of foods - pollutants
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7. WHAT IS GC/MS?
• Gas chromatography/mass spectrometry (GC/MS) is the synergistic
combination of two powerful analytic techniques.
• The gas chromatography separates the components of a mixture in time
• The mass spectrometer provides information that aids in the structural
identification of each component
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8. WHAT IS GC/MS?
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9. THE GC/MS INTERFACE
• Transports the effluent from the gas chromatograph to the mass
spectrometer
• Analyte must not condense in the interface
• Analyte may not decompose before entering the mass spectrometer ion
source
• The gas load entering the ion source must be within pumping capacity of
the mass spectrometer
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10. GC/MS INTERFACES
• Capillary Columns
• Macrobore and Packed Columns
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11. CAPILLARY COLUMNS
• Insert exit end of column into ion source
• Under normal operating conditions, the mass spectrometer can handle the
entire effluent of the column
• Must heat the capillary column to prevent condensation
• Surface of columns must be inactive
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12. MACROBORE AND PACKED
COLUMNS
• Effluent must be reduced before entering ion source
• Splitting the effluent results in a loss of sensitivity
• Enrichment devices are used
• Jet Separators are most common
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13. JET SEPARATOR
• Two capillary tubes aligned with a small space between them. (1 mm)
• A vacuum is created between the two tubes using a rotary pump
• The GC effluent enters the vacuum region, those molecules which continue in
the same direction enter the second capillary tube and continue to the ion source
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14. JET SEPARATOR
• The carrier gas molecules are more easily diverted
from the linear path by collisions
• The analyte molecules are much larger and carry more
momentum
• The surface of the separator must be inactive and a
reasonably even temperature
• Prone to leaks
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15. 15
Chromatography
Interface (GC-MS) Jet
Separator
• The MS is used both
quantitatively and
qualitatively
• Major interface
problem – carrier gas
dilution
• Jet separator or porous
tube (separates analyte
from carrier gas)
• GC (use capillary
columns)

16. RESOLUTION AND MASS
ACCURACY
• With a modern mass spectrometer, it is possible to measure the mass of an ion
to 1ppm with a resolution of 100,000 or better
• GC/MS scanning conditions are limited to 5-10 ppm mass accuracy and
resolution is only between 2,000 and 10,000.
• These limitations are usually sufficient to allow for only a few reasonable and
possible compositions
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17. USES FOR GC/MS
• May separate, analyze and identify unknown mixutres
• May separate, and analyze known mixtures
• For sample GC/MS experiments check out:
• http://www.lehigh.edu/~ingcms/ingcms.html
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18. THANK YOU
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