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SAMPLE HANDLING | AIR SAMPLING
Thermal Desorption Unit Tubes
Table I: Comparison of thermal desorption tube and canister sampling
for VOCs.
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Thermal Desorption Unit (TDU) Tubes vs. Canister Sampling
Which VOC Sampling Technique is Right for You?
Thermal desorption unit (TDU) tubes provide a complementary option to canisters for
sampling VOCs. Both techniques have advantages and disadvantages, and their features
must be evaluated for suitability relative to the sampling environment and analytical capa-
bilities. Table I outlines the similarities and differences between these techniques; use this
handy comparison to determine which equipment is best for you.
Similarities Between Thermal Desorption Tubes and Canisters
• Reusable sampling device.
• Long product lifetime.
• Long-term sample stability.
• Blank certification required prior to sampling.
• Sample concentration required before GC-MS analysis.
• Dry purge helpful to remove moisture before GC injection.
• ppt sensitivity.
• Method acceptance.
• Collection of wide range of VOCs with single device.
• Useful for screening of unknowns.
• Leak tightness critical to maintaining sample integrity and preventing contamination of a clean device.
Differences Between Thermal Desorption Tubes and Canisters
Thermal Desorption Tubes Canisters
Methods U.S. EPA TO-17
ASTM D6196
ISO 16017
ISO 16000-6
NIOSH 2549
U.S. EPA TO-14A, TO-15
ASTM D5466
OSHA PV2120
NIOSH Protocol Draft
World-wide acceptance Gold standard for U.S. ambient air market
Applications Ambient air, indoor air, industrial hygiene
Material emissions
Food & flavor
Chemical weapons
Ambient air, indoor air, vapor intrusion,
emergency response
C3 to C30 <C3 to ~C10
Handling Lightweight for personal sampling and general
ease of use
Larger and heavier; more costly to ship
Sampling Active sampling with sampling pump or diffusive
sampling without pump is possible with determined
diffusion coefficients for each compound.
Passive sampling, no sampling pump
required. Long-term sampling possible
without battery to recharge.
Integrated sampling only Grab & integrated sampling
Concentrated sample Whole air
Proper sorbent selection recommended in methodology. N/A
Must sample below sorbent breakthrough volumes to
avoid sample loss and irreversible adsorption on sorbent
N/A
Large sample volumes >100L Sample volume is function of canister size,
15 L max
Analysis Tube dimensions are instrument specific Compatiblewithallmanufacturersample
concentrators
One injection, more injections possible for some
instrumentation
Multiple sample injections
Concentration range ppt to ppm ppt to ppm
Some sorbents prone to artifact formation. Low blanks when properly cleaned.
Storage Sample storage at 4 °C recommended for multibed tubes
to prevent potential migration of compounds to more
retentive sorbent, which may be difficult to recover.
Room temperature
Cleaning Analytical process automatically cleans tube for reuse.
Cleans as it analyzes. Conditioning/cleaning and analysis
incorporated in one thermal desorption unit.
Canister cleaning requires separate
equipment as additional step prior to
background certification and sampling.
Cost $50–130 each $200–700 each
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A Guide toWhole Air
Canister Sampling:
Equipment Needed and Practical
Techniques for Collecting
Air Samples