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OverviewOverview
Gas Chromatograph calibration Syringe Technique VOC exposure limit Site Assessment
Potential sites Soil Gas Surveys Field Analysis
Gas Chromatograph calibration Syringe Technique VOC exposure limit Site Assessment
Potential sites Soil Gas Surveys Field Analysis
Gas Chromatograph
injection volumeinjection volume
Output chromatogram converted to peak areas and peak times
Convert peak area to mass using injection of known mass (standard) peak area is proportional to mass injected mass injected can be converted to concentration
given _________ _________ Alternately use peak area (PA) as surrogate
for mass
Gas Chromatograph Calibration We can use the headspace sample from source vials
to calibrate the GC. We will use the ideal gas law and the vapor pressure
of the VOCs.
liquidliquid
gasgasOctaneOctane
AcetoneAcetone
TolueneToluene
vapor pressureat 25 °C
vapor pressureat 25 °C
1.88 kPa1.88 kPa
24 kPa24 kPa
3.8 kPa3.8 kPa
MWMW
114.23 g114.23 g
58.08 g58.08 g
92.14 g92.14 g
densitydensity
0.71 g/mL0.71 g/mL
0.79 g/mL0.79 g/mL
0.87 g/mL0.87 g/mL
Example Calibration: Octane
n
PVRT
n PVRT
K298
KmolkPaL
8.31
L10 x 100 kPa 1.88n
6-
K298 Kmol
kPaL8.31
L10 x 100 kPa 1.88n
6-
nmol 75.9 =mol 10 x 9.57n 9 nmol 75.9 =mol 10 x 9.57n 9
Calculate moles, mass, and equivalent liquid volume of 100 µL headspace sampleCalculate moles, mass, and equivalent liquid volume of 100 µL headspace sample
g 8.67g 10 x 8.67mol
114.23gmol 10 x 75.9 69 g 8.67g 10 x 8.67
mol114.23g
mol 10 x 75.9 69
nL 12.2 = L 10 x .221g 0.71L 10
g 10 x 8.67 93
6
nL 12.2 = L 10 x .221g 0.71L 10
g 10 x 8.67 93
6
liquidoctane
gas
KmolkPaL
8.31R
Kmol
kPaL8.31R
VOC Contaminated Site Map
Report gas concentrations in mg/m3. Example: Given a peak area of 1 x 104 from
an injection volume of 100 µL, calculate the concentration in mg/m3. Assume the peak area from the source vial injections was 2 x 108.
38
4
mg/m 4.3g/L 4.3PA10 x 2g 8.67
L 100PA 1x10
sample PAsample PA
calibration PAcalibration PAsample volumesample volume
mass injected for calibrationmass injected for calibration
Syringe Technique
The Problem: VOC vapors sorb to glass barrel, Teflon plunger, and
stainless steel needle The Solution:
Remove GC needle. Purge syringe 10 times with room air to remove any residual
VOCs. Put on sample needle. (continued)
Syringe Technique: solutionSyringe Technique: solution
Insert into sample bottle (with syringe at zero volume). Fill syringe fully with gas and purge syringe contents back into
the source bottle (repeat 3 times). Fill syringe and adjust to 100 µL. Close syringe valve and remove syringe from sample vial and
remove sample needle. Put on GC needle. Instruct GC to measure sample. Insert needle in injection port, open syringe valve, inject
sample, hit enter button all as quickly as possible. Remove syringe from the GC injection port.
Insert into sample bottle (with syringe at zero volume). Fill syringe fully with gas and purge syringe contents back into
the source bottle (repeat 3 times). Fill syringe and adjust to 100 µL. Close syringe valve and remove syringe from sample vial and
remove sample needle. Put on GC needle. Instruct GC to measure sample. Insert needle in injection port, open syringe valve, inject
sample, hit enter button all as quickly as possible. Remove syringe from the GC injection port.
Equilibrate with headspace
Eliminate needle carryover
Octane Exposure Limits
OSHA PEL (Permissible exposure level) 500 ppm TWA (approximately ____ mg/m3)
LC50 CAS# 111-65-9: Inhalation, rat: LC50 =118
g/m3/4H.
336-
6
g/m 86.5m
L 1000L 10 x 100g 10 x 8.67
concentration in octane source vialconcentration in octane source vial
500(1 m3 of air is approximately 1 kg)
Site Assessment
Contaminated soil, a global problem Difficult to assess subsurface contamination
can’t see it 3-d problem even with lots of monitoring wells can
miss important subsurface features.
Expensive to decontaminate sites competing national priorities highest priority needs to be prevention
Hazardous Waste Site Surveys
loading zones hydraulically operated lifts accidental spills
storage tanks vegetative distress
herbicide application hazardous materials
stained soil
fill materialused to hide evidence of spillmay contain hazardous substances
water and sewer linesprovide pathways for migration of subsurface contaminants
Soil Gas Survey
Effective screening technique for mapping the extent of VOCs
Indicates location of contaminant sources
Advantagesrapidlow costminimal disturbance to siteno waste generatedadaptable to site conditions
Advantagesrapidlow costminimal disturbance to siteno waste generatedadaptable to site conditions
Disadvantagesdetection limits may be too highsome compounds may not be detectedfield results are semi-quantitative
Disadvantagesdetection limits may be too highsome compounds may not be detectedfield results are semi-quantitative
Sampling Matrix
Soil Gas Survey: Methods Place hollow, small diameter probe in soil Apply vacuum to probe Extract soil pore gas Take a sample of soil pore gas using:
syringe - on-site gas chromatograph analysis Tedlar bag - on-site or off-site analysis
unaffected by most compounds impermeable to gas exchange
stainless steel adsorption tube - quantitative laboratory analysis
Soil Gas SamplingSoil Gas Sampling
Static sampling can be done two ways: An in-situ adsorbent (usually an activated charcoal rod) is buried in
the soil for a period of days to weeks. The adsorbent is retrieved and analyzed at a laboratory for VOCs.
Samples are collected from containers placed in the surface soil and analyzed using portable analytical instruments.
Concentrations in soil gas are affected by dissolution, adsorption, and partitioning. Partitioning refers to the ratio of component found in a saturated
vapor above an aqueous solution to the amount in the solution. Contaminants can also be adsorbed onto inorganic soil components or "dissolved" in organic soil components.
Static sampling can be done two ways: An in-situ adsorbent (usually an activated charcoal rod) is buried in
the soil for a period of days to weeks. The adsorbent is retrieved and analyzed at a laboratory for VOCs.
Samples are collected from containers placed in the surface soil and analyzed using portable analytical instruments.
Concentrations in soil gas are affected by dissolution, adsorption, and partitioning. Partitioning refers to the ratio of component found in a saturated
vapor above an aqueous solution to the amount in the solution. Contaminants can also be adsorbed onto inorganic soil components or "dissolved" in organic soil components.
Field Analysis Field Analysis
Less accurate and less sensitive than laboratory analysis!
Immediate results Examples
Portable Gas chromatograph Photoionization Air Monitor Flame Ionization Detector Test kits
Less accurate and less sensitive than laboratory analysis!
Immediate results Examples
Portable Gas chromatograph Photoionization Air Monitor Flame Ionization Detector Test kits
Analysis Matrix
http://www.perkin-elmer.com/photo/pvac.html#VOyager
Portable Gas ChromatographPortable Gas Chromatograph
Portable GC contains a built-in 3-column configuration with
isothermal oven which provides optimized fast GC analysis for up to 40 volatile organic compounds (VOC).
a miniaturized PID/ECD dual detection system which allows monitoring at 1-10 PPB levels of a wide range of aromatic, chloroalkene, and chloroalkane solvents.
Portable GC contains a built-in 3-column configuration with
isothermal oven which provides optimized fast GC analysis for up to 40 volatile organic compounds (VOC).
a miniaturized PID/ECD dual detection system which allows monitoring at 1-10 PPB levels of a wide range of aromatic, chloroalkene, and chloroalkane solvents. MDLMDL
Photoionization Air MonitorPhotoionization Air Monitor
The 2020 hand-held Total VOC air analyzer weighs just 1.75 lb. (0.79 kg).
Sample is drawn via the internal pump
Results are displayed on the built-in LCD.
The operating concentration range is 0.5 - 2000 PPM.
The 2020 hand-held Total VOC air analyzer weighs just 1.75 lb. (0.79 kg).
Sample is drawn via the internal pump
Results are displayed on the built-in LCD.
The operating concentration range is 0.5 - 2000 PPM.
Flame Ionization DetectorFlame Ionization Detector
The Micro FID weighs 8.1 lb. (3.7 kg.),
the smallest and lightest datalogging Flame Ionization Detector (FID) available.
The concentration range is 0.1 - 50, 000 PPM with a response time of less than 3 seconds.
The Micro FID weighs 8.1 lb. (3.7 kg.),
the smallest and lightest datalogging Flame Ionization Detector (FID) available.
The concentration range is 0.1 - 50, 000 PPM with a response time of less than 3 seconds.
Potential Sites
Underground fuel storage tanks home owner beware! gasoline stations
Waste management facilities Chemical storage facilities Liquid waste lagoons Injection wells Chemical transfer facilities
http://www.cha-llp.com/tankmgt.htm
Underground Storage TanksUnderground Storage Tanks
Leaking underground storage tanks are a significant source of soil and water contamination in the United States.
New regulations went into effect in 1998 Many facilities removed underground tanks and
replaced them with double walled tanks or above ground tanks for petroleum product and chemical storage.
Leaking underground storage tanks are a significant source of soil and water contamination in the United States.
New regulations went into effect in 1998 Many facilities removed underground tanks and
replaced them with double walled tanks or above ground tanks for petroleum product and chemical storage.