1. Pure Carrier Gas Grades (subjective)
Grade He H2 N2
Analytical % N/A N/A
Research
UHP HP
Zero*
* “Instrument Zero”  usually no other impurities except THC (Total HydroCarbons) Often used as a zero gas for Total Hydrocarbon Analyzers.

2. Typical Impurities in Pure Gas Grades That Can Affect Detectors
Electron Capture Detector
ECD
Oxygen and water can reduce detector response and halocarbons can give rise to baseline noise and negative peaks.
Flame Ionization FID Hydrocarbons in carrier and
Detector fuel gases can cause baseline
noise and reduced detector
sensitivity. Oxygen and water
can cause column deterioration.

3. Gas Chromatography Applications: (two major roles)
Performing separations
Analysis using or peak height or peak area
Qualitative Analysis using retention times, tR’s
Limited by numerous variables
May not lead to positive ID of species present, but rather to the absence of species
e.g., absence of new peaks when evaluating purification of organics or in QC and QA

4. Quantitative Analysis
Relative accuracy of < 1%
(1) Based on Peak Height
Variables closely controlled:
temperature
flow rate
sample injection rate h

5. (2) Based on Peak Area
Areas independent of:
temperature
flow rate
sample injection rate
Most GC’s have digital electronic integrators

6. Separation of Proteins
Size Exclusion
Chromatography
Excellent for polymers
and large biopolymers
Detector response

7. Size Exclusion Chromatography
Large molecules pass
through column faster
than small molecules
Stationary phase: cross-linked
polystyrene polymer
Mobile Phase: varies
Column: X 25 cm (typical)
Detector: UV absorption

8. Typical SEC Column Containing Polymerized “Fingers”

9. Gas Chromatography – Mass Spectrometry
Hyphenated Methods
GC is coupled with another technique:
e.g., GC-MS, GC-FTIR, GC-NMR, etc.
Gas Chromatography – Mass Spectrometry
Problem:
GC requires relatively high pressures (∼ 40 psi)
MS requires very high vacuum (∼ μtorr)
Solution:
Use GC capillary column with jet separator or “skimmer” at the interface

10. Schematic of a Jet Separator
Sample and
He carrier gas
from GC
Sample to MS
Entire chamber at He
Silica
nozzle

11. Jet Separator in Action

12. Schematic of Ion Trap Detector

13. 2.5 cm

14. GC-MS Spectrum of Benzene (MW = 78)