Transcript Environmental Chemistry - Robert Morris University

Industrial Hygiene
Analysis of Volatile Organic
Compounds
Copyright © 2008 by DBS
Contents
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Organic pollutants
Techniques
Sampling
Analytical methods
Direct reading
Organic Trace Pollutants
Include
• Naturally occurring compounds from decomposition of OM
• Anthropogenic pollutants
• Degradation and inter-reaction products of pollutants
• Substances derived from sewage treatment
Typical analysis:
• Individual compounds or groups of compounds
• Total analysis of all organic components
• Field screening for specific pollutants prior to lab analysis
• Qualitative identification of trade products in spills and discharges
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Number of VOC species and low concentration make IAQ
measurements challenging
Question
Compounds causing widespread environmental problems
include toxicity, resistance to biodegradation and
bioaccumulation. List the types of organic compounds which fall
under these catagories
Pesticides, chlorinated solvents, PCBs. dioxins, edochrine disruptors
Techniques
GC
• Gas Chromatography – organic compounds have significant
volatility
HPLC
• High Performance Liquid Chromatography – increasing in use
UV-Vis Spec
• Ultraviolet-Visible Spectrometry – useful for groups of
compounds since absorptivities vary little between similar
compounds
Sampling
Storage Considerations
(a)
(b)
(c)
(d)
(e)
Volatility – containers should be completely filled and kept at
sub-ambient temperatures
Microbial degradation – store at < 0 °C to lower further
Photolysis – store in the dark (e.g. organochlorines)
Contamination – glass should be used (no plastics)
Adsorption – analyze ASAP (low-solubility organics)
Sampling
Sampling and Analytical Methods
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Typical analysis:
– Individual compounds or groups of compounds
– Total analysis of all organic components
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EPA “TO” methods (Toxic Organic Series)
Sampling
Total VOC Vapors
1. Direct injection of air sample into GC-MS
• Requires portable GC and a skilled chemist for fine-tuning
2. Solid sorbent tube collection followed by lab analysis (concentrates VOC)
• TENAX resin in SS or glass tube (EPA method TO-1)
– absorbs non-polar and polar compounds btp. 60 – 100 °C
– Retention volume is different for each VOC “break-through volume”
– Sample volumes difficult to determine due to unknowns
– Either extracted into solvent or thermally desorbed into carrier gas for
analysis
3. Evacuated container sampling
• VOCs are subsequently concentrated on selected sorbents or cryogenically
trapped (EPA method TO-14)
– Summa elecropolished container walls improve stability
Analytical Methods
Gas Chromatography
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Chromatographic separation by
differential partition of components
between stationary phase (liquid
adsorbed or bonded to a solid) and
mobile phase (gas)
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Separate based on solubility and VP
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High separation efficiency
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Highly sensitive detectors
Analytical Methods
Detectors
Detector
Applications
Thermal Conductivity
Universal detector for organics
Flame Ionization
Universal detector for organics
Electron Capture
Specific to atoms with high e- affinity e.g. Cl
e.g. chlorinated pesticides, PCBs
Hall electrolytic conductivity
Specific for halogens, N and S
e.g. pesticides, trihalomethanes
Thermionic
Element-specific for compounds containing N and P
e.g. pesticides
Flame photometric
Element-specific for compounds containing NS and P
e.g. pesticides
Photo-ionization
Specific tocompounds containing aromatic rings or double bons
e.g. solvents
Mass spectrometric
All organic compounds
Analytical Methods
Columns and Stationary Phases
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Narrow-bore Capillary Columns
Wide-bore Capillary columns
Packed Columns
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Compounds of interest have high M and low volatilities, require high
temperatures
Best separation when stationary phase has same polarity as analyte
– Fuel oils on non-polar columns
– Pesticides and chlorinated solvents on medium-polarity columns
– Dioxins on highly polar columns
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Decreasing separation
efficiency
Question
How would you confirm that a peak is due to a single
component rather than two components with identical retention
times?
Chromatogram should be made on two columns of differing polarities
Many procedures specifiy the use of a second confirmational column
Analytical Methods
Example Procedures
• Most involve extraction prior to analysis
– Separate interferences
– Concentrates
– GC would get blocked if injected with water
• For analysis of individual components expected at low
concentrations (e.g. pesticides) further pre-treatment may be
necessary
e.g. DDT
p,p’-DDT 70-80%
o, p’-DDT 15-20 %
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DDT is a mixture
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Environmental scamples
would also contain metabolic
breakdown products
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p, p’-DDE
p, p’-DDD
Multi-component mixture
even without other species
expected in water!!!
Possible interference from
PCBs, similar pesticides etc.
o,p’-DDD
p,p’-DDD 1-4 %
Analytical Methods
DDT - Pretreatment
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Hexane extraction into 3 aliquots of 30 mL of solvent
Drying extract in a 5 g column Na2SO4
Concentration to 1 mL using an evaporator
Clean-up of extract by colum chromatography
– Al2O3 (removes polar components)
– AgNO3 (retains unsaturated C compounds)
– Na2SO4
• Concentration to 1 mL using an evaporator
• Overall C.F. x 100
detection limit ng L-1
Question
Clean-up of the extract simplifies the chromatogram. What is a
further advantage?
Protection of the column and detector from contamination
Analytical Methods
Quantification
• External standards
– Compare the peak area of unknown with areas of a series of
solutions used to form a calibration curve (library)
– Not ideal as injection volumes may be different
• Internal standards
– Produces peak close to but resolved from unknown species
– Variation in volume shows up as change in peak area of
internal standard
– Results are normalized to internal standard peak area
– Also useful to quantify losses during pretreatment and
calculate %-age recovery
Analytical Methods
Direct Reading
Direct Reading Instruments
• Flame Ionization Detector (organic vapor analyzer)
– e.g. Foxborro OVA
• Photoionization Detector (PID)
– e.g. ppbRAE
Summary
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A
Books
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Hess-Kosa, K. (2002) Indoor Air Quality. Lewis Publishers.
Leslie, G.B. and Lunau, F.W. (1992) Indoor Air Pollution: Problems
and Priorities. Cambridge University Press.
Turco, R.P. (2002) Earth Under Seige: From Air Pollution to Global
Change. Oxford University Press, London.
References
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Ayoko, G.A., Volatile Organic Compounds in Indoor Environments. In:
Pluscke, P. (2004) Indoor Air Pollution (Handbook of Environmental Chemistry.
Springer-Verlag, New York.
Salthammer, T. and Uhde, E (2009) Organic Indoor Air Pollutants. Wiley-VCH.