this lesson

Gas Chromatography in the
detection of Volatile Organic
Voltatile Organic Compounds
• Volatile organic compounds (VOCs) are gases
emitted from a variety of products
– Paints
– Pesticides
– Aerosol sprays and cleaners
• Exposure to these chemicals can affect health.
Eye and respiratory tract irritation
Visual disorders
Cause cancer in animals
Common VOCs
Most common
Methylene Chloride
Animal carcinogen (converted to
carbon monoxide in the body)
Human carcinogen
Used in dry cleaning
Voltatile Organic Compounds
• EPA has set the Permissible Exposure Level of
0.75 ppm and an action level of 0.5 ppm.
– VOC levels are two to five times higher inside than
• Exposure can be reduced by increasing
ventilation and storing materials with VOCs in
closed containers
• VOCs can be detected by gas chromatography
Gas Chromatography
• Separate and detect compounds in gas phase
– Can analyze liquids if they can be volatilized without
• Solid-phase Microextraction (SPME)
– Gas sample exposed to a fiber coated with
extraction phase (commonly silica)
– Fiber placed in inlet and heated to desorb analyte
• Static Headspace Sampling
– Gas sample is sealed into a vessel, warmed, and
injected directly into injection port
Gas Chromatography
• Mobile Phase: inert carrier gas nitrogen
• Stationary Phase: column coated with active
– Packed column: fine silica beads coated with liquid or
solid active material
– Capillary column: inner column coated with active
material; long column wound into a small coil
• Retention time: time it takes for analyte to exit
the column
– Analyte components that are adsorbed more by the
stationary phase have longer retention times
• Flame Ionization Detection (FID):
– Sample hydrocarbon is combusted with oxygen and
ionized, which releases electrons
– Current measured is proportional to amount of analyte
– Good general detector for many compounds
• Electron Capture Detection (ECD):
– Emitted beta electrons collide with nitrogen carrier gas
removing an electron
– Analyte captures an electron reducing detected current
– Analyte concentration is proportional to degree of
electron capture
– Best for highly electronegative halogenated samples
• Photoionization Detection (PID)
– Shine UV light on sample, causes it to emit an
– Current measured is proportional to concentration
if extent of ionization is the same for all analytes
– Good for hydrocarbon samples
• Mass Spectrometry
– Interface with GC to ionize sample after it elutes
from column
– Detect m/z ratio of compounds
– Gives better information about chemical identity
Gas Chromatograph of an air sample taken from a synthetic organic chemistry lab
Portable GC
• Goal: Take instrument to places of interest to
monitor air quality
– Conduct indoor air sampling studies
– Monitoring on-site emission levels
• Challenge: Miniaturize components
– Minimize power consumption for outdoor uses
Experimental Results
Gas chromatograph for a sample of indoor air collected by SPME analyzed for n-alkanes