Title: Interfacing Gas Chromatography with Mass Spectroscopy and Infra Red Spectroscopy
1Interfacing Gas Chromatography with Mass
Spectroscopy and Infra Red Spectroscopy
- Is this a large expensive detector.
- Or a separation prior to analysis.
2Early 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
3Principles 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
4Interfacing 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
5Application of a Selective Detector - Modern
- The detector monitors the column effluent
continuously - Need computers to control instruments and store
spectral data for display of spectrum and
chromatograms
6Interfacing Gas Chromatography and Mass
Spectroscopy (GC/MS)
7GC/ 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
8GC/ 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
9What 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
10What is GC/MS?
11What is GC/MS?
12The 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
13GC/MS Interfaces
- Capillary Columns
- Macrobore and Packed Columns
14Capillary 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
15Macrobore 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
16Jet 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
17Jet 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
18Resolution 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
19Resolution and Mass Accuracy
- Resolution can be increased by restricting the
height and the width of the ion beam - A compromise must be made between minimizing mass
interference and signal intensity for low levels
of material - Gas chromatograph eliminates most compounds that
cause mass interference. - Principle cause of peak overlap is the internal
mass standard.
20Uses 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
21Complex Mass Spectrometer Detectors
- Display modes - real time or computer
reconstructed - Each has a choice of total ion current
chromatogram or selected ion current chromatogram - Each can be generated on to a computer screen for
print out
22Ion Trap Detector
- compact - less expensive than quadropole
- simplest mass detector for use in GC
- ions are created form eluted sample by electron
impact or chemical ionization - stored in radio-frequency field
- ions injected from the storage area to a detector
23ITD
- Ejection is controlled so the scanning of mass to
charge ratio is possible
24Gas Chromatography Infrared Spectrometry (GC/IR)
- Instrumentation/Interface
- Advantages
- Problems/Cons
- Solutions
- Practical Applications
25Infrared Spectrometry
- Is especially useful for qualitative analysis of
functional groups and other structural features - measuring concentrations is possible
- establish identity of unknown compound with
standard
26Instrumentation/Interface
- Infrared Spectrophotometer determines the
relative strengths and positions of the infrared
region and plots the information on calibrated
paper - Gas Chromatograph partitions the sample as it
passes through the column - The two can be linked through glass column or
vacuum tubes and other devices on more expensive
equipment
27Fourier-Transform Infrared Spectroscopy (FTIR)
- Overcomes the problem
- of scanning for a collected sample
- or monitoring one wavelength
28Fourier Transform IR
- Mechanically simple
- Fast, sensitive, accurate
- Internal calibration
- No tracking errors or stray light
29FTIR
- Analyze all wavelengths simultaneously
- signal decoded to generate complete spectrum
- can be done quickly
- better resolution
- more resolution
- However, . . .
30Gas Chromatography / Infrared Spectrometry
- Capillary GC with IR specs can enable the
separation and identifying the compounds - The interface between the column and the detector
is the main detail - Small pipe (length 10-40 cm, diameter 1-3 mm)
connected to column by narrow tubing - Transmission of radiation occurs by multiple
reflection off the wall
31GC/ IR
- Light pipe is heated in order to rid condensation
and maximize path length for enhanced sensitivity - This also minimizes the dead volume to lessen
band broadening - Detector - highly sensitivity, liquid nitrogen
cooled - Scanning is started and a brief delay is needed
for compound to travel form the detector region
to the IR cell
32More on General GCIR
- Very sensitive
- very expensive
- sample recovery
33Practical Uses
- Pharmaceutical
- Industrial
- DNA Analysis of blood samples, other fluids
- many others
34INTERFACE to Multiwavelength UV / VIS Detectors
- Monitor several specific wavelengths set by
colored dyes attached (DNA) - Flow through a multiwavelength detector and
optical multichannel analyzer
35Conclusion
- Gas chromatography can be effectively coupled
with uv/vis detectors for monitoring dye labels,
and infra-red spectroscopy and mass spectroscopy
to more effectively analyze mixtures. - This is also true for liquid chromatography,
although the interfaces present different
problems.
36(No Transcript)