Thermal Desorption:
A Practical Applications Guide
I. Environmental Monitoring &
Exposure to Chemicals at Work
2nd Edition
www.markes.com
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Introduction to Markes International Ltd
What is analytical TD?
Formed in 1997, Markes International is world leader in
the development and manufacture of analytical thermal
desorption (TD) instrumentation and associated sampling
equipment for measuring VOCs and semi-volatiles in air
& materials.
Markes has pioneered major TD innovations such as
quantitative re-collection for repeat analysis
(SecureTD-Q™), TubeTAG™ RFID tube labels,
DiffLok™ enabling technology for robust tube
automation and cryogen-free analysis of multiple
canister air samples. All these innovations feature in
Markes’ well known modular range of TD instruments:
UNITY™, U
addition, the TD-100™. Other ground-breaking TD
products from Markes International include the
twin-trap TT24-7™ for continuous, online air monitoring,
and unique sampling accessories such as the
Micro-chamber/Thermal Extractor™ and HS5-TD™
for liquid and solid samples.
Markes’ TD units can be seamlessly combined with all
major brands of GC and GC/MS to provide trace or high
level monitoring solutions.
LTRA™, Air Server™ and the most recent
Analytical thermal desorption is a sample introduction
technique for GC and GC/MS, which uses heat and a
flow of inert gas, rather than an organic solvent, to
extract/desorb analytes from the sample media,
delivering them directly to the gas chromatograph.
Since the early 1980s, TD has provided the ultimate
versatile sample introduction technology for GC, by
combining selective concentration enhancement with
direct extraction into the carrier gas and efficient
transfer/injection, all in one fully automated and
labour-saving package.
Markes International Ltd, UK headquarters
1
Applications
Environmental monitoring
Thermal desorption is now recognised as the technique
of choice for environmental and workplace air
monitoring. Relevant standard methods include: EN ISO
16017, EN 14662 (parts 1 & 4), prEN 13649, ASTM
D6196, US EPA TO-17 and NIOSH 2549. Related
applications include monitoring chemical warfare agents
(CWA) in demilitarisation/destruction facilities & civilian
locations (counter-terrorism).
TD is also routinely used for monitoring volatile and
semi-volatile organic compounds [(S)VOCs] in products
and materials. Examples include residual solvents in
packaging & pharmaceuticals, material emissions testing
and food, flavour & fragrance profiling.
This publication presents several real world applications
in environmental air monitoring and occupational health
& safety. Accompanying publications cover the
application areas of:
• Food, flavour, fragrance & odour profiling
• Defence & forensic
• Chemical emissions from products & materials
• Atmospheric research
• Ambient/urban air monitoring
• Industrial (stack) emissions testing
• Odour monitoring
• Indoor air quality
• Soil gas & vapour intrusion assessment
• Trace volatiles and odours in water
• Workplace air monitoring/industrial hygiene
• Personal exposure monitoring (inhalation)
• Biological exposure assessment (breath testing)
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Atmospheric research
Ions: 35
79
127
30 ml of air from bubbles in the ice core collected in canisters.
Analysis by TD-GC/MS in NCI mode. Low ppt detection limits
Background:
Markes thermal desorption instrumentation is used
extensively in atmospheric research for monitoring
trace organic vapours. For example:
• Global migration of pollution
• Research into stratospheric chemistry
• Marine research: Studying the oceans as a
potential ‘sink’ or reservoir for air pollutants
• Historical pollution data e.g. levels of freons in
air bubbles trapped in polar ice
Markes TD systems offer best available desorption
efficiency allowing splitless operation & optimum
sensitivity without liquid cryogen
Std. methods: EN ISO 16017-1, ASTM D 6196, US
EPA TO-17, (tubes) or US EPA TO-15 (canisters)
Typical analytical conditions:
Sampling: Pumped multi-sorbent tube or canister
TD: Series 2 (U
LTRA-)UNITY or TD-100 for tubes,
UNITY-CIA 8 (+ dryer) for canisters
Dry purge if no dryer used during sampling
Splitless desorption
Trap: U-T16GHG-2S or U-T15ATA-2S
Analysis by GC/MS using SIM, NCI or TOF MS
References: TDTS 81 (TO-15), 86 (TO-17) & 87
(ultra-volatile freons & other greenhouse gases)
3
SafeLok™ – Specialist sample tubes for
trace detection
Threaded DiffLok
inserts protect
both ends of the
sorbent tube
Background:
SafeLok samplers have the same sorbent capacity
as standard tubes but incorporate Markes patented*
diffusion-locking (DiffLok) technology at both ends
of the tube to prevent artefact ingress.
With the same external dimensions as standard
TD tubes, SafeLok tubes are uniquely suited to
monitoring ultra-low concentration environments
e.g. at the North Pole or mid-Pacific. Samples
are protected from contamination during
storage/transport & during subsequent TD-GC/MS
analysis in a conventional laboratory.
SafeLok samplers incorporate Markes patented DiffLok technology
to prevent artifact ingress. This aids trace level monitoring
TubeTAG
All Markes tubes, including SafeLok tubes, are now
available with or without TubeTAG electronic (RFID)
tube labels. TubeTAG offers fail-safe tracking of tubes
in transit for field monitoring. It also enhances tube
traceability for GLP and laboratory
accreditation. Recorded
information includes: sorbent
details, number of thermal
cycles, date of packing, etc.
* GB 2337513
US 6,564,656 B1
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Implementation of TubeTAG with SafeLok tubes
significantly enhances the traceability of key
samples.
Std methods: EN ISO 16017-1, US EPA TO-17,
ASTM D 6196
Typical analytical conditions:
Sampling: Pumped multi-sorbent SafeLok tube
TD: Series 2 (U
LTRA-)UNITY or TD-100
Dry purge
Splitless desorption
Trap: Select according to target analyte range
Analysis by GC/MS
References: TDTS 61 (diffusion locking technology)
& Markes TD accessories & consumables catalogue
TO-17: ‘Air toxics’ in urban air using
pumped sampling onto sorbent tubes
3
4
1 Propylene
2 Dichlorodifluoromethane
3 1,2–Dichlorotetrafluoroethane
4 Methyl chloride
5 1,2-Dichloroethane
6 1,3–Butadiene
7 Vinyl chloride
8 Methyl bromide (bromomethane)
9 Chloroethane
10 Trichlorotrifluoroethane
(Freon 113)
11 Ethanol
12 1,2-Dichloroethlyene
13 1,1,2-Trichlorotrifluoroethane
14 Acetone
15 Carbon disulfide
16 Isopropyl alcohol
17 Methylene chloride
18 Tert-butyl methyl ether
19 n-Hexane
20 1,1-Dichloroethane
Pumped sampling of 1 L of 1 ppb air toxics standard analysed
splitless using ATA tubes. Inset shows close-up of extracted
mass ion 45 for IPA, demonstrating excellent peak shape
21 Vinyl acetate
22 Cis-1,2-Dichloroethylene
23 Methyl ethyl ketone
24 Ethyl acetate
25 Tetrahydrofuran
26 Chloroform
27 1,1,1-Trichloroethane
28 Cyclohexane
29 Carbon tetrachloride
30 Benzene
31 n-Heptane
32 Trichloroethylene
33 1,2–Dichloropropane
34 1,4-Dioxane
35 Bromodichloromethane
36 Trans-1,3-dichloropropene
37 Methyl isobutyl ketone
38 Toluene
39 Cis-1,3-Dichloropropene
40 Trans-1,2-Dichloroethylene
41 1,1,2-Trichloroethane
42 Tetrachloroethylene
43 Methyl n-butyl ketone
44 Dibromochloromethane
45 1,2–Dibromoethane
46 Chlorobenzene
47 Xylene
48 Xylene
49 Xylene
50 Styrene
51 Tribromomethane
52 1,1,2,2-Tetrachloroethane
53 1,2,4-Trimethylbenzene
54 1,3,5-Trimethylbenzene
55 1-Ethyl-4-methyl benzene
56 Ethylbenzene
57 1,2-Dichlorobenzene
58 1,3-Dichlorobenzene
59 alpha-Chloromethylbenzene
60 1,4-Dichlorobenzene
61 1,2,4-Trichlorobenzene
62 Hexachloro-1,3-butadiene
Background:
US Clean Air Act regulations have identified specific
‘Hazardous Air Pollutants’ (HAPs) also known as
‘air toxics’. These analytes cover a wide range of
polarities & volatilities & are most effectively
monitored using pumped sampling onto multisorbent tubes with automated TD-GC/MS (scan)
analysis.
Markes cryogen-free TD technology meets all the
requirements of TO-17 compliant air toxics analysis
Std. method: US EPA Method TO-17
Typical analytical conditions:
Sampling: Pumped sorbent tube (20-50 ml/min)
Sorbent: ‘Air Toxics’ (ATA) or ‘Universal’ tubes
TD system: Series 2 (U
LTRA-)UNITY or TD-100
On or offline dry purge before desorption
Desorption: 10 mins at 320ºC
Trap: U-T15ATA-2S (Air toxics/soil gas): +25 to
330ºC
Split: Splitless or low split during trap desorption
only
Column: 60 m x 0.32 mm x >1 µm for ‘volatiles’
Analysis: GC/MS (scan)
References: Markes Technical Support Document
for TO-17, TDTS 86 (using sorbent tubes to
monitor air toxics in air as per TO-17)
5
MTS-32™ Sequential tube sampler
Office air
Laboratory air
Semi-rural outside air
1 Methanol
2 2-methyl butane
3 Ethanol
4 Acetone
5 Isopropyl alcohol
6 2-methyl pentane
7 3-methyl pentane
8 Hexane
9 Ethyl acetate
10 2-methyl hexane
11 Cyclohexane
12 3-methyl hexane
13 Heptane
14 Acetic acid
15 1-methyl-2-propanol
16 Toluene
17 Hexanal
18 Xylene
19 Xylene
20 Alpha-pinene
21 Cyclohexanone
22 Alpha-myrcene
23 D-limonene
24 Phenol
25 Menthol
26 2-phenoxy ethanol
Three 1 L real air samples collected using ‘Universal’ sorbent
tubes and desorbed splitless using TO-17 conditions as above
Applying TO-17:
TO-17-type methods, based on pumped air
monitoring with multi-sorbent tubes, can be applied
to ambient indoor and outdoor air samples. They
facilitate simultaneous analysis of a wide range of
apolar & polar organic vapours including veryvolatile, volatile & semi-volatile components.
Markes TD systems uniquely feature quantitative
re-collection of any split flow (primary or secondary)
for repeat analysis and simple validation of recovery
per standard methods, such as ASTM D6196
(SecureTD-Q).
Example analytical conditions are listed above
TO-17 performance data using Markes TD
technology with GC/MS (scan):
Retention volumes for lightest components (propene,
methyl chloride):
• >2 L on ‘Air Toxic’ (ATA) tubes at 25ºC
• >1 L on ‘Universal’ tubes at 25ºC
Detection limits: <0.1 ppb for all compounds in scan
Linearity: Typical R
2
values of 0.99 at low ppb
Precision: Typical % RSDs <6
Carryover: <0.1%
SecureTD-Q confirms quantitative recovery across
the volatility range
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Soil gas and vapour intrusion assessment
Profiles of soil gas contaminated with kerosene (JP-8) sampled
using sorbent tubes (red) and canisters (blue). Data presented
courtesy of Air Toxics Inc., CA, USA
Second desorption
Shows no carryover
First desorption
First and second desorptions of a Soil Gas tube used to sample
diesel vapour in contaminated soil
Background:
Soil gas measurements are used to assess the
potential risk to human health from vapour intrusion
into nearby buildings & to identify sources for
mitigation & liability management. Key target
analytes include gasoline & middle distillate fuels
plus solvents e.g. dry cleaning or degreasing agents.
Canister, bag and sorbent tube sampling
methodologies are used.
Markes Soil Gas tubes allow quantitative recovery of
the widest range of potential target analytes, without
water interference. Markes’ TD systems also benefit
this application by accommodating tube & canister
samples on the same analytical platform & by offering
re-collection for repeat analysis of tube samples.
Standard methods: US EPA Methods TO-17 or TO-15
Typical analytical conditions:
Pumped sampling onto Soil Gas tubes
TD system: Series 2 (ULTRA-)UNITY or TD-100
Desorption: 300ºC for 5 mins
Trap: U-T15ATA-2S (Air toxics/soil gas):+25 to 330ºC
Splitless to 5,000:1 (double) split depending on
contamination level
Apolar analytical capillary column
Analysis: GC/MS (scan)
References: TDTS 80 (Soil gas) & Hayes, H. C.,
et al. (2007), Evaluation of sorbent methodology
for petroleum impacted site investigations,
Proc. Air & Waste Man. Assoc. conf. on
vapor intrusion
7
In situ monitoring of underground
contamination
Soil probes arranged in a grid pattern around an industrial site
allow low-cost mapping of contaminated ground
VOC-Mole soil probe fitted with a
sorbent tube configured for diffusive
(passive) sampling
Background:
Underground fuel or chemical leaks present a grave
environmental risk. Markes VOC-Mole™ soil probes
containing standard diffusive or pumped tube
samplers allow cost-effective, in situ screening of
large areas of land including active production sites.
They can also be placed along the length of fuel
pipelines to provide early warning of a leak. VOCMoles configured with diffusive (passive) samplers
are easy to deploy & allow rapid (e.g. 15 minute)
or longer term (24 to 48 hour) exposure. The soil
probes themselves can be left in situ if regular
monitoring is required. Subsequent automated
TD-GC/MS analysis allows identification of the
nature, source & spread of ground contamination.
Typical analytical conditions:
Sampling: Sorbent tubes used diffusively inside
soil probes
®
Sorbent: Tenax
TD system: Series 2 (U
TA or Soil Gas tubes
LTRA-)UNITY or TD-100
Desorption: 5 mins at 280ºC
Trap: Tenax TA or U-T15ATA-2S: +25ºC to 320ºC
Splitless to 5000:1 double split, depending on the
contamination level
Analysis: GC/MS (scan) or GC-FID
References: TDTS 29 (monitoring soil pollution
using soil probes) & TDTS 80 (Soil gas analysis)
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TO-15 ‘air toxics’ in urban air
using canisters
9.40
1 Propylene
2 Dichlorodifluoromethane
3 1,2-
Dichlorotetrafluoroethane
4 Methyl chloride
5 Chloroethane
6 1,3-Butadiene
7 Vinyl chloride
8 Methyl bromide
(bromomethane)
9 1,2-Dichloroethane
10 Trichlorotrifluoroethane
®
113)
(Freon
11 Ethanol
12 1,1-Dichloroethylene
13 1,1,2-
Trichlorotrifluoroethane
14 Acetone
15 Carbon disulfide
16 Isopropyl alcohol
17 Methylene chloride
18 Tert-butyl methyl ether
19 Cis-1,2-dichloroethylene
Splitless analysis of 1 L x 1 ppb air toxics standard in a canister.
Inset shows close-up of extracted mass ion 45 for IPA,
demonstrating excellent peak shape.
9.60
20 n-Hexane
21 1,1-Dichloroethane
22 Vinyl acetate
23 Trans-1,2-dichloroethylene
24 Methyl ethyl ketone
25 Ethyl acetate
26 Tetrahydrofuran
27 Chloroform
28 1,1,1-Trichloroethane
29 Cyclohexane
30 Carbon tetrachloride
31 Benzene
32 n-Heptane
33 Trichloroethylene
34 1,2-Dichloropropane
35 1,4-Dioxane
36 Bromodichloromethane
37 Cis-1,3-dichloropropene
38 Methyl isobutyl ketone
39 Toluene
40 Trans-1,3-Dichloropropene
41 1,1,2-Trichloroethane
42 Tetrachloroethylene
43 Methyl n-butyl ketone
44 Dibromochloromethane
45 1,2-Dibromoethane
46 Chlorobenzene
47)
48) Xylene
49)
50)
51 Styrene
52 Tribromomethane
53 1,1,2,2-Tetrachloroethane
54 Trimethylbenzene
55 Trimethylbenzene
56 1-Ethyl-4-methyl benzene
57 Dichlorobenzene
58 Dichlorobenzene
59 Chloromethylbenzene
(alpha)
60 Dichlorobenzene
61 1,2,4-Trichlorobenzene
62 Hexachloro-1,3-butadiene
Background:
For the ultimate in air sampling flexibility (canisters,
bags & sorbent tubes), Markes TD systems offer full
compliance with US EPA Methods TO-15 and TO-17.
Systems offer automated sequencing for up to
8 canisters/bags together with manual or automated
tube desorption. Electrically-cooled focusing
(no liquid cryogen required), versatile water
management & uniquely efficient trap desorption all
combine to minimize running costs, optimize uptime
and ensure uncompromised analytical performance
(sensitivity, repeatability, etc.).
Standard method: US EPA TO-15
(supersedes TO-14)
Typical analytical conditions:
TD system: Series 2 UNITY-CIA 8
Volume sampled from canister: 100 ml to 1 L
Trap: U-T15ATA-2S or U-T16GHG-2S: 25ºC. 40ºC/s
to 320ºC (3 mins)
Split: Splitless or low split during trap desorption only
60 m x 0.32 mm ID x 1.80 µm thick film capillary
column for ‘volatiles’
Analysis: GC/MS (scan)
Reference: TDTS 81 (Analysis of canister air
samples using cryogen-free thermal desorption
in compliance with US EPA method TO-15)
9
1 Propylene
2 Dichlorodifluoromethane
3 1,2-
Dichlorotetrafluoroethane
4 Methyl chloride
5 Chloroethane
6 1,3-Butadiene
7 Vinyl chloride
8 Methyl bromide
(bromomethane)
9 1,2-Dichloroethane
10 Trichlorotrifluoroethane
®
113)
(Freon
11 Ethanol
12 1,1-Dichloroethylene
13 1,1,2-
Trichlorotrifluoroethane
14 Acetone
15 Carbon disulfide
16 Isopropyl alcohol
17 Methylene chloride
18 Tert-butyl methyl ether
19 Cis-1,2-dichloroethylene
20 n-Hexane
21 1,1-Dichloroethane
22 Vinyl acetate
23 Trans-1,2-dichloroethylene
24 Methyl ethyl ketone
25 Ethyl acetate
26 Tetrahydrofuran
27 Chloroform
28 1,1,1-Trichloroethane
29 Cyclohexane
30 Carbon tetrachloride
31 Benzene
32 n-Heptane
33 Trichloroethylene
34 1,2-Dichloropropane
35 1,4-Dioxane
36 Bromodichloromethane
37 Cis-1,3-dichloropropene
38 Methyl isobutyl ketone
39 Toluene
40 Trans-1,3-dichloropropene
41 1,1,2-Trichloroethane
42 Tetrachloroethylene
43 Methyl n-butyl ketone
44 Dibromochloromethane
45 1,2-Dibromoethane
46 Chlorobenzene
47)
48) Xylene
49)
50)
51 Styrene
52 Tribromomethane
53 1,1,2,2-Tetrachloroethane
54 Trimethylbenzene
55 Trimethylbenzene
56 1-Ethyl-4-methyl benzene
57 Dichlorobenzene
58 Dichlorobenzene
59 Chloromethylbenzene
(alpha)
60 Dichlorobenzene
61 1,2,4-Trichlorobenzene
62 Hexachloro-1,3-butadiene
Splitless analysis of 1 L x 1 ppb air
toxics standard in a canister using
a series 2 UNITY-CIA 8 system
configured for analysis of trace
ultra-volatile greenhouse gases
Applying TO-15:
Canisters are ideally suited to ultra-volatile organics
such as freons & C
hydrocarbons which are difficult
2
to trap on sorbent tubes at ambient temperature.
They also offer convenient grab sampling.
Markes TD systems are uniquely suited to split or
splitless analysis of volatiles in canisters and operate
cryogen-free.
TO-15 performance data using series 2 UNITYCIA 8 with GC/MS (scan):
Retention volumes for lightest components (propene,
methylchloride):
• >2 L on focusing trap U-T16GHG-2S at 25ºC
• >1 L on focusing trap U-T15ATA-2S at 25ºC
Detection limits: <0.1 ppb for all compounds in
scan mode
2
Linearity: Typical R
values of 0.99 at low ppb
Precision: Typical % RSDs <6
Carryover: <0.1%*
* N.B. Canisters themselves are prone to incomplete
recovery of polar sepcies and components boiling
above n-C
, such as naphthalene. They may
8/10
also be difficult to clean.
10
Monitoring trace ultra-volatiles with high
global warming/ozone depletion potential
SF
6
N2O
Extracted ions 69 (black), 172 (green) and 30 (red) from a full
scan analysis of 25 ml of a 100 ppb standard of CF
and N2O
, C2F6, SF
4
6
Background:
Some of the regulations developed in response to
the Kyoto protocol require the monitoring of trace
level ultra-volatile compounds with high global
warming & ozone depletion potential such as
perfluorinated hydrocarbons (CF4, C2F6, etc), the
tracer gas SF
and N2O. These compounds boil from
6
-128°C and are extremely difficult to
trap/concentrate and measure at low levels.
Markes online or canister-based TD systems feature
cryogen-free operation and efficient splitless
desorption and are uniquely suited to monitoring
these compounds on- or offline. Detection limits
range down to 0.05 - 0.2 ppt for SF
and C2F
6
6
respectively, using TD-GC/MS (quadrupole, SIM)
Typical analytical conditions:
Sample volume: 25 ml (CF
(SF
, C2F6)
6
), 150 ml (N2O) to 1 L
4
System: Series 2 UNITY-CIA 8
Trap: U-T16GHG-2S: -30ºC. 40ºC/s to 320ºC (3 mins)
Splitless desorption
50 m x 0.53 mm ID alumina PLOT column + 5 m x
0.18 mm restrictor
Analysis: GC/MS (SIM), or ECD or TOF MS
Reference: TDTS 87 (A cryogen-free method for
measuring trace greenhouse gases in air)
11
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‘Ozone precursors’ (C2to C10hydrocarbons)
in ambient air
PLOT Column
BP1 Column
1 Ethane
2 Ethylene
3 Propane
4 Propylene
5 Isobutane
6 n-Butane
7 Acetylene
8 trans-2-Butene
9 1-Butene
10 cis-2-Butene
11 Cyclopentane
12 Isopentane
13 n-Pentane
14 trans-2-Pentene
15 1-Pentene
16 cis-2-pentene
17 2,2-Dimethylbutane
18 2,3-Dimethylbutane
19 2-Methylpentane
Splitless desorption of 56-compound US EPA mix of ozone
precursors using series 2 UNITY-Air Server with dual
column/dual FID GC and Deans switch
12
20 3-Methylpentane
21 Isoprene
22 2-Methyl-1-Pentene
23 Methylcyclopentane
25 2,4-Dimethylpentane
26 Benzene
27 Cyclohexane
28 2-Methylhexane
29 2,3-Dimethylpentane
30 3-Methylhexane
31 2,2,4-Trimethylpentane
32 n-Heptane
33 Methylcyclohexane
34 2,3,4-Trimethylpentane
35 Toluene
36 2-Methylheptane
37 3-Methylheptane
38 n-Octane
39 Ethylbenzene
40 m/p-Xylene
41 Styrene
42 o-Xylene
43 n-Nonane
44 Isopropylbenzene
45 n-Propylbenzene
46 m-Ethyltoluene
47 p-Ethyltoluene
48 1,3,5-Trimethylbenzene
49 o-Ethyltoluene
50 1,2,4-Trimethylbenzene
51 n-Decane
52 1,2,3-Trimethylbenzene
53 m-Diethylbenzene
54 p-Diethylbenzene
55 n-Undecane
56 n-Dodecane
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Background:
C
to C10hydrocarbons, originating from car
2
exhausts, have been identified as precursors to the
formation of street level ozone and urban smog. US,
European and other regulators require round-theclock monitoring of these compounds in major urban
centres during the summer months. Series 2 UNITYAir Server allows continuous, unattended and
cryogen-free monitoring at low to sub-ppb levels and
automatic sequencing between a minimum of 3
channels (sample, standard & blank). Markes series
2 TD systems offer splitless desorption & uniquely
high cryogen-free retention volumes for ultra-volatiles
such as acetylene & ethane. Systems are operated in
remote, unattended monitoring stations, with data
accessed via telemetry and processed/validated at
remote network control centres.
Official guidance: US EPA Tech. Assist. Document for
sampling and analysis of ozone precursors
Typical analytical conditions:
Sampling: Online from manifold at 25 ml/min
Sampling volume: 400 - 1000 ml
TD system: Series 2 UNITY-Air Server with dryer
Trap: U-T17O3P-2S: -30 to 320ºC at 40ºC/sec
Splitless desorption
GC configuration: Either GC, dual column, dual FID
& Deans switch, or single FID with “PoraPLOT” type
column
Reference: TDTS 16
Online monitoring of diurnal variation of
pollutants in ambient air
Key:
Blue (3 am),
Red (12 noon),
Green (5:30 pm)
Ethane
Pentane
Ethene
Acetylene
Propane
Online monitoring of semi-rural/semi-industrial
ambient air using series 2 UNITY-Air Server
GC/FID and GS-GasPro-type ‘PoraPLOT’
column showing how the VOC profile
varies with time
2-Methyl propane
Propene
Butane
1-Butene
Background:
Markes series 2 UNITY-Air Server systems offer
cryogen-free, online monitoring of trace volatiles in
ambient air, using GC/FID or GC/MS. The optimised
focusing trap contains an extended (60 mm) bed of
multiple sorbents which is held at -30ºC and
desorbed in backflush mode at rates up to 100ºC/s.
This enables ultra-volatile hydrocarbons/freons to be
quantitatively retained and efficiently released at the
same time as much higher boiling components, such
as naphthalene, trimethyl benzene & hexachloro
butadiene.
A wide range of vapour-phase components (ozone
precursors, hazardous air pollutants and odour
components) can all be monitored simultaneously.
Typical analytical conditions:
Sample: A 200 to 1000 ml volume of air sampled at
10-25 ml/min (optional dryer)
System: Series 2 UNITY-Air Server (with Nafion
®
dryer)
Trap: U-T17O3P-2S: -30ºC to +25ºC. 40ºC/s to
320ºC (3 mins)
Splitless desorption
GS-GasPro™ 30 m x 0.32 mm capillary column for
‘volatiles’
Analysis: GC/FID
References: TDTS 16 (online round-the-clock air
monitoring), 32 (analysis of sulphur compounds),
81 (analysis of canister air samples with US EPA
method TO-15) & 87 (monitoring trace greenhouse
gases in air)
13
Mapping criteria pollutants in ambient
air by diffusive sampling
Rouen (Northern France).
Interpolated benzene
isoconcentration plot.
Measurements performed
from 19-23/01/98
RFID tagged sorbent tube (TubeTAG)
References: TDTS 10 (diffusive monitoring of ambient
air), TDTS 01 (uptake rates), TDTS 42 (radial diffusion
for TD) & TubeTAG brochure
Background:
Accurate mapping of pollution levels across a major
urban centre requires hundreds of sampling points.
Diffusive (passive) samplers are low-cost and easy
to deploy facilitating large-scale and/or detailed
environmental surveys. Markes unique TubeTAG
electronic tube labelling system benefits large scale
field monitoring studies, by eliminating transcription
errors & enhancing traceability.
Series 2 (U
LTRA-)UNITY and TD-100 systems feature
the option of onboard read/write of tagged tubes for
complete, error-free automation
Std. methods: EN 14662-4, EN ISO 16017-2, ASTM
D 6196
Typical analytical conditions:
Sampling: Diffusive (passive)
Sorbent: Carbograph™ 1TD (benzene), Carbopack™
X (1,3-butadiene)
Monitoring time: 7-14 days (axial), 4-6 hours (radial)
TD system: Series 2 (U
LTRA-)UNITY or TD-100 with
onboard TubeTAG read/write
Desorption: 5-10 minutes at 320ºC
Trap: Carbograph 1TD/Carbopack X from +30
to 320ºC
Split: ~20:1 during trap desorption only
Analysis by GC-FID or GC/MS
14
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Odorous industrial emissions
2
S
6
H
2
C
2
S
6
H
2
C
2
S
6
H
2
C
Reproducibility
(% RSD at
20 ppb)
QA/QC sample
20 ppb
10 ppb
Compound
H2S
CH3SH
C2H6S
C2H6S
2
S
2
SH
3
H
CH
S
6
H
2
C
S
2
SH
H
3
S
6
CH
H
2
C
S
SH
S
2
3
H
6
H
2
CH
C
Detection
limit
(ppb)
0.15 0.9973 4.1 93
0.15 0.9983 1.8 108
0.15 0.9999 0.8 107
0.10 0.9993 0.8 108
Linearity
(at ppb
levels)
Recovery
(% at 80%
relative
humidity)
Background:
Highly odorous sulphur compounds in industrial or
landfill emissions must be controlled to sub or lowppb levels. These very volatile & highly reactive
compounds are usually sampled online or in
canisters/bags & analysed using TD-GC/PFPD.
Markes series 2 UNITY is a uniquely versatile TD
platform. The standard system allows selection of
low flow path temperatures without installation of
special valving. This facilitates analysis of thermally
labile components such as mercaptans & other
odorous species. Markes online TD systems have
also demonstrated exceptional analytical
performance and reliability in unattended field
operation
Std. method: Korean Government Guidance Method
- Standard Method for Off-Odour Analysis (2005)
Typical analytical conditions:
Sample volume: 100-500 ml
TD system: Series 2 UNITY-Air Server with dryer
TD flowpath: 80ºC
Trap: U-T14H2S-2S (H
S): -30 to 250ºC
2
Split: 12:1 during trap desorption only
Column: 60 m x 0.32 mm x 5.0 µm, apolar
Analysis: GC/PFPD
References: TDTS 32 (analysis of sulphur compounds),
Ki-Pong Song, et al., (2007), Korean Journal of Odour
search and Engineering, Vol 6 (1), 33-39
15
Biogenic emissions: Vapour-phase organic
chemicals from moulds, plants, etc.
Monoterpenes & terpenoids
Sesquiterpenes
Terpenoids
ppb-Level terpenes in air above leaf litter
Background:
Plants, moulds, animals & other life forms emit VOCs
& contribute to the ‘cocktail’ of organic vapours in
ambient air. Monoterpenes are emitted by pine trees
on sunny days, possibly as a defence against
potential photochemical damage. These reactive
hydrocarbons are monitored using pumped sampling
onto inert tubes packed with Tenax TA followed by
TD-GC/MS analysis. Similarly, the detection of
methyl benzoate in indoor air can indicate mould
growth & geosmin in water indicates the presence of
certain algae (see also page 20). The profile of
vapour-phase organics can also sometimes be used
to identify the precise species of plant, mould, etc
and/or the phase of growth.
Markes series 2 (U
LTRA-)UNITY or TD-100 systems
offer quantitative re-collection for repeat analysis
(SecureTD-Q). This is an invaluable feature for
validating quantitative recovery of biogenic emission
components (some of which are extremely reactive)
through the analytical system.
Typical analytical conditions:
Sampling: Pumped sorbent tube
®
Sorbent: Tenax TA in stainless/Silcosteel
TD system: Series 2 (U
LTRA-)UNITY or TD-100
tube
Desorption: 5 mins at 220ºC
Trap: U-T9TNX-2S (Tenax): -10 to 250ºC
Split: Low split during trap desorption only
Analysis: GC/MS (scan)
16
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Odours & toxics in landfill gas
Toluene
Redesorption blank
Butan-2-ol
Chloroethane
Vinyl chloride
1-pentene
Dimethyl sulphide
Furan
1,1-dichloroethane
Carbon disulphide
Butan-1-ol
Benzene
1,1- & 1,2-dichloroethene
Trichloroethene
1,1,1-trichloroethane
Dimethyl disulphide
100 ml landfill gas with trace target analytes & many major
components identified
1 Vinyl chloride (Toxic)
2 1,3-Butadiene (Toxic)
3 Methyl Mmercaptan
(Odour)
4 Chloroethane (Toxic)
5 1-Pentene (Odour)
6 Furan (Toxic)
7 Ethyl mercaptan
(Odour)
8 1,1- Dichloroethene
(Toxic)
9 Dimethylsulphide
(Odour)
10 Carbon disulphide
(Odour) (Toxic)
11 1,2-Dichloroethene
(Toxic)
12 1,1-Dichloroethane
(Toxic)
13 Propyl mercaptan
(Odour)
14 Tetrachloromethane
(Toxic)
References: TDTS 32 (sulphur compounds) &
TDTS 47 (analysis of landfill gas)
a-pinene
Decane
Butanoic acid ethyl ester
Nonane
Xylene
15 Benzene (Toxic)
16 Trichloroethene (Toxic)
17 Butyl mercaptan
(Odour)
18 Dimethyldisulphide
(Odour)
19 Ethylbutyrate (Odour)
20 2-Butoxyethanol
(Toxic)
Background:
New regulations in Europe & several Asian countries
require monitoring of trace toxic & odorous
compounds in landfill gas. Such analysis is either
carried out online (see page 15) or by drawing 100200 ml samples through a special sorbent tube using
a simple bellows pump or large gas syringe.
Limonene
The patented inert valve within series 2 (U
LTRA-)
UNITY and TD-100 facilitates subsequent offline
analysis of the sampled tubes by allowing low flow
path temperatures to be selected e.g. 120ºC in this
example. Quantitative recovery of labile odorous
analytes, such as ethanethiol, can also be validated
using SecureTD-Q.
Official guidance: UK Env. Agency publication
‘Monitoring trace components in landfill gas.’
Typical analytical conditions:
Sample volume: 100-500 ml
Sorbent: Silcosteel tube with Tenax TA/UniCarb™
(at same temp as gas)
TD system: Series 2 (U
LTRA-)UNITY or TD-100
TD flowpath: 120ºC
Trap: Sulphur trap -15 to 220ºC (40º/min)
Benzene
Split: From 10:1 to 50:1
Column: 60 m x 0.25 mm ID x 1.4 µm
film DBVRX
Ethanethiol
Analysis: GC/MS (scan)
SecureTD-Q: Repeat analysis validates
quantitative recovery of ethanethiol
through the TD flowpath
17
Software tools for minimising GC/MS
background & enhancing trace analysis
Analysis of a trace level landfill gas standard
using the thick film capillary column
described above. ClearView completely
eliminates interference from column bleed
ClearView™
Original data
ClearView
reprocessed data
S/N ~3:1
Unidentified
Peak at 16.48 mins
unidentified in original data
Peak at 16.48 mins
automatically identified as
thiophene in ClearView
reprocessed data
S/N 30:1
Thiophene
Background:
ClearView™ uses a sophisticated algorithm to
accurately & dynamically compensate for
chromatographic background as it changes
throughout a run. The process works even if the
same mass ion is present in both the background
and the peaks of interest. Original data files are
retained intact so implementation of ClearView is
risk free.
ClearView™ works with all makes of GC/MS & can be
used to reprocess stored data files individually or in
batches. Reprocessing takes seconds. ClearView can
also be executed/implemented within the
environment of several leading brands of GC/MS
data processing software during an automated
sequence of analyses.
Key advantages include:
• Improvement in spectral purity for enhanced
automatic identification of trace components
• Reduced signal to noise for improved
sensitivity/detection
• Facilitates scanning from low masses
• Productivity: Reduces/de-skills data
interpretation, boosting sample throughput
• Compatible with scan, SIM/scan & SIM data
(see page 20)
References: TDTS 83 & 85 (Using ClearView
reprocessing to enhance trace GC/MS analysis)
18
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HS-TD: Simple & sensitive analysis of
purgeable VOCs in water
Analysis by HS-TD
Analysis by HS
Trace level purgeable VOCs in drinking water analysed by
conventional HS (black) and HS-TD (blue)
Background:
Headspace–thermal desorption (HS-TD) brings
together two of the most powerful GC introduction
techniques & offers optimum sensitivity for tracelevel volatiles in solid, liquid and gas-phase samples.
Pressurised headspace vapours are transferred from
the sample vial & into the UNITY 2 focusing trap
before being desorbed/injected into the GC(MS) in a
reverse flow of carrier gas. The process of
headspace vapour transfer & focusing can be done in
a single stage, or repeated several times to optimise
sensitivity before the trap is finally desorbed to
trigger GC analysis.
Repeated pressurisation & evacuation of headspace
vials also extends the compatible analyte volatility
range relative to conventional equilibrium
headspace. This allows lower boiling compounds to
be measured at the same time as the volatiles.
HS-TD options available for UNITY 2 include:
• The cost-effective manual HS5
module (5 vial capacity)
• A range of leading brand HS
autosamplers
Typical analytical
conditions are shown
below
Reference: HS5-TD
brochure
19
Trace (ppt) level odorants in drinking
water using HS-TD with ClearView
Without ClearView data reprocessing
MIB
5 ppt level odorants in drinking water analysed by HS-TD-GC/MS
(SIM) shown with & without ClearView reprocessing
Trichloroanisole (1)
With ClearView data reprocessing
Reference: TDTS 78 (ppt-levels
of odorants in drinking water
using HS-TD)
Geosmin
TCA (2)
Background:
Drinking water is prone to contamination by
naturally-occurring odorous compounds such as
geosmin, methyl-i-borneol & trihaloanisoles. These
components produce a musty/’earthy’ smell that is
detectable by consumers at concentration levels
down to 10 ppt.
HS-TD offers a simple, innovative & readilyautomated approach to routine analysis of odorants
in drinking water. Detection limits down to 1 ppt can
be achieved using conventional 20 ml HS vials/caps
and GC/MS (quad/SIM). ClearView reprocessing
software optimises signal-to-noise (sensitivity) at the
lowest levels. Further enhancements could be
possible e.g. by employing aluminium-coated vial
caps, by including a salting-out step and/or by using
enhanced MS technology.
Typical analytical conditions:
HS vials: 45-50ºC
Sample cycles:10
U-T2GPH-2S trap held at 30ºC (purgeables), & 50ºC
(odorants)
60 m x 0.32 mm x 1.8 µm film ‘volatiles’ column for
purgeables
60 m x 0.25 mm ID x 0.25µm film 1701 capillary
column for odorants
Analysis: GC/MS (scan or SIM)
20
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Profiling indoor air quality (IAQ)
Hexane
Freon 113
Trichlorofluoromethane
Dichloromethane
1,1-difluoro-1-chloroethane
1,1,1,2-tetrafluoroethane
Dichlorodifluoromethane
1,1-difluoroethane
Propanol
Isopentane
Ethanol
Ethyl acetate
Acetone
Tetrachloromethane
Clean indoor air pumped onto a multi-sorbent tube & analysed
by TD-GC/MS
Typical analytical conditions:
Sampling: Pumped sampling: 2-20 L
Sorbent: Tenax TA or an IAQ tube (quartz/Tenax TA/
Carbopack X)
TD system: Series 2 (U
LTRA-)UNITY or TD-100
Desorption: 5 mins at 280ºC (depends on sorbent)
Trap: To match tube (-30 to 300ºC)
Split: During trap desorption only ~15:1
Analysis: GC/MS (scan)
Toluene
Trimethylbenzene
Ethyl benzene
o/p xylene
a-pinene
Tetrachloroethane
Ethylcyclohexane
Styrene
Decane
Benzene
Hexanal
Methylcyclohexane
Nonanal
Benzyl alcohol
Undecane
Dodecane
Limonene
Background:
Most people in the developed world spend an
estimated 70-90% of their time indoors or in
vehicles. Regulators & scientists around the world
are increasingly concerned about the impact of poor
indoor (or in-vehicle) air quality (IAQ/IVAQ) on
human health & comfort.
Sources of indoor pollutants include construction
(or car trim) materials, furnishings, cleaning
products, fuels, general consumer goods &
human/animal activity (cooking, smoking, etc.)
Tridecane
Tetradecane
Recent environmental developments (e.g. the EC
directive on Energy Performance of Buildings) are
putting further pressure on IAQ by reducing building
ventilation rates.
TD is used extensively for monitoring IAQ & for
related applications such as materials emissions
testing. In this example, pumped tube samplers
were used with subsequent TD-GC/MS analysis for
profiling of ppt-ppb level VOCs.
Std. methods: US EPA Method TO-17, EN ISO
16017-1, ASTM D 6196
References: TDTS 28 (monitoring
indoor air), Thermal Desorption:
A Practical Applications Guide. II.
Residual Volatiles & Materials
Emissions Testing
21
Personal exposure indoors
Personal
Indoor
Outdoor
Poor indoor air quality & high personal exposure in this home were
linked to a diesel car parked in a garage under the living space
Markes TubeTAG
technology facilitates large
scale surveys of IAQ and
human exposure, by
making it easier to record
& check tube & sampling
information without
transcription errors
Background:
TD-GC/MS is used for several applications relating to
poor IAQ and ‘sick building syndrome’. In this case
residents were complaining of poor air quality in
their home. Diffusive sampling with ‘axial’ sorbent
tubes was used to monitor indoor & outdoor air
quality at the house and to monitor the personal
exposure of residents.
Diffusive monitors are unobtrusive, low cost, simple
to deploy (no pumps) & available with Markes
unique TubeTAG technology. This makes them ideal
for large-scale personal exposure studies.
Std. methods: EN 14662-4, EN ISO 16017-2, ASTM
D6196
Typical analytical conditions:
Sampling: Diffusive sampling
Sorbent: Carbograph 1TD, Carbopack X or Tenax TA
depending on target analyte range
TD system: Series 2 (U
LTRA-)UNITY or TD-100
Desorption: 5 mins at 320ºC
Trap: U-T2GPH-2S or to match tube sorbent
Split: ~10:1 during trap desorption only
Analysis: GC/MS (scan)
References: TDTS 10 (diffusive sampling in indoor
air), TDTS 01 (uptake rates)
22
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Building ventilation tests with
tracer gases
Different PFCs
placed in separate
rooms allow the
monitoring of air
exchange
6
monitored using
PMCH
PMCP
PDCB
PMCP
PMCH
Perfluorocarbon tracer gases
monitored using TD-GC/ECD
or TD-GC/MS
First Floor
Ground Floor
PDCB
0.1 ppb SF
online TD-GC/MS as described
on page 11
Background:
SF
and perfluorocarbons (PFCs) are commonly used
6
as tracer gases to determine ventilation rates &
pathways in buildings & vehicles. The rise &
subsequent decay of tracer gas concentrations is
monitored using on- or offline TD with GC and
electron capture detection (ECD) or GC/MS. SF6can
be sampled using low volume (100-500 ml)
sampling onto strong sorbent tubes but is more
commonly monitored online (see page 11).
Different PFCs (e.g. perfluoromethyl cyclohexane
(PMCH), perfluoromethyl cyclopentane (PMCP) &
perfluorodimethyl cyclobutane (PDCB)) placed in
different locations within a building allow the
monitoring of air exchange. They are sampled
diffusively or with pumps onto tubes packed with
Carbograph 1TD or Carbopack B™.
Typical analytical conditions for PFCs:
Sampling: diffusive or pumped
Sorbent: 40-60 mesh Carbograph 1 TD
TD system: Series 2 (U
LTRA-)UNITY or TD-100
Desorption: 5 mins at 320ºC
Trap: Carbograph 1 TD -30 to 300ºC
Split: Splitless or low split
Analysis: GC/MS or GC/ECD
Reference: H. Bloemen et al,
(1992), Ventilation rate and
exchange of air in dwellings,
RIVM rpt, NL.
23
Monitoring car cabin air
Car cabin air 23°C
TVOC 3.7 ppm
Toluene
m-/p-xylene
n-Hexane
MEK
Methylcyclohexane
Benzene
NN DMF
Heptane
Cyclohexane
Styrene
Ethyl benzene
n-Octane
Isooctane
Car cabin air 40°C
TVOC 9.7 ppm
Toluene
m-/p-xylene
Ethyl benzene
NN DMF
Methylcyclohexane
Styrene
Air from the cabin of a small car showing a complex range of
VOCs and high total-VOC levels
Dimethylbenylamine
11
C
12
C
n-Decane
13
C
11/12
C
Trimethyl benzene
o-Xylene
n-Nonane
Ethyl toluene
n-decane
Dimethylbenzylamine
Trimethylbenzene
o-xylene
n-nonane
Silyl ester
13
Cubebene/Copaene
n-C
2-(2-butoxy-ethoxy)ethanol
12
C
11/12
C
11
13
C
C
13
14
n-C
n-C
2-(2-butoxy-ethoxy)ethanol
Silyl ester
Copaene
Dodecane
Background:
Car cabins are small confined spaces. Vapour-phase
(S)VOC levels can build up, especially in parked cars
on a hot day. Car manufacturers & their suppliers are
currently focused on improving the quality of cabin
air and reducing emissions from vehicle interior trim
components. IVAQ samples are typically sampled
using pumped, multi-sorbent tubes and analysed by
TD-GC/MS.
Markes TD systems are ideally suited to IVAQ
monitoring. They offer simultaneous analysis of VOCs
& SVOCs & feature a short, inert flow path that can
be set at low or moderate temperatures, if required,
to optimise recovery of labile odorous analytes such
as amines.
Std. methods: EN ISO 16017-1, ISO 16000-6, ASTM
D6196.
Typical analytical conditions:
Sampling: Pumped sampling of 2-10 L volume
Sorbent: Tenax TA or an “IAQ” tube (e.g. quartz,
Tenax, Carbopack X)
TD system: Series 2 (U
LTRA-)UNITY or TD-100
Desorption: 6 mins at 280ºC
Trap: U-T12ME-2S (“IAQ”) Tenax TA or
Tenax/Carbopack X (-30 to 300ºC)
Split: 50-200:1 (single or double split)
Analysis: GC/MS (scan)
Reference: TDTS 33 (profiling car cabin air)
24
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Vapour-phase semi-volatiles by thermal
desorption: n-C40& phthalates
Phthalate standard mixture with internal standard
Re-collection & repeat analysis
Hexadecane
Diethyl phthalate
Dimethyl phthalate
Dibutyl phthalate
Diethyl-hexyl phthalate
Di-n-decyl phthalate
Markes TD systems are compatible with the analysis of semivolatiles such as n-C40 and didecyl phthalate. SecureTD-Q
(quantitative re-collection for repeat analysis) provides a
convenient means of demonstrating quantitative recovery
through the system
C
14
C
16
C
18
C
20
Recovery validated using SecureTD-Q
C
24
C
28
C
32
Hydrocarbon standard:
C
36
Sample
C
40
Background:
Thermal desorption is usually associated with
analysis of volatile organic chemicals. However, the
short, inert, heated flow path of Markes TD systems
also ensures quantitative recovery of semi-volatiles
such as n-C40& didecyl phthalate.
Markes SecureTD-Q technology uniquely offers
quantitative re-collection of split flows from both
tube & trap desorption onto a single conditioned
sorbent tube. This provides a convenient means of
demonstrating quantitative recovery of all analytes
through the entire TD system as described in
standard methods such as ASTM D6196.
Typical analytical conditions:
Sampling: Pumped sorbent tube
Sorbent: Quartz wool with 1 or 2 carbon blacks
Sample volume: Up to 100 L at up to 500 ml/min
TD system: Series 2 U
LTRA-UNITY
Desorption: 15 mins at 360ºC
Trap: High boilers trap (U-T1HBL-2S): -30 to 375ºC
Split: Typically 50:2.5 during trap desorption only
Column: 30 m x 0.25 mm ID x 0.25 mm film apolar
Analysis: GC/MS (SIM or scan)
Reference: TDTS 53 (quantitative recovery of
semi-volatiles)
25
Vapour-phase semi-volatiles by thermal
desorption: PAHs & PCBs
PAH standard mixture
Benzo(a)pyrene
Chrysene
Benzo(a)anthracene
Quantitative recovery of polychlorinated biphenyls (PCBs) and
poly aromatic hydrocarbons (PAHs), including benzo-a-pyrene,
through series 2 ULTRA-UNITY demonstrated using SecureTD-Q
PCB standard mixture
(Aroclor 1260)
Benzo(k)fluoranthene
Benzo(b)fluoranthene
R
Dibenzo(a,h)anthracene
Benzo(g,h,i)perylene
Indeno(1,2,3-cd)pyrene
e-collection & repeat analysis
Sample
Re-collection
& repeat analysis
Background:
Markes’ thermal desorbers owe
their unsurpassed performance
with semi-volatiles to the short,
inert, uniformly-heated flow path &
patented TD heated valve used in each
(ULTRA-)UNITY 2 and TD-100 system.
It is the unique valve & flow path configuration of
Markes TD systems that also allows quantitative
recovery of both inlet (tube desorption) & outlet
(trap desorption) split flow onto the same
conditioned sorbent tube for repeat analysis &
validation of analyte recovery (i.e. SecureTD-Q).
Typical analytical conditions:
As shown on page 25.
Reference: TDTS 53 (quantitative
recovery of semi-volatiles)
26
Sample
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Industrial (stack) emissions – solvents
Second re-collected sample
First re-collected sample
Original sample
Quantitative stack analysis carried out using double splitting & an
overall split ratio of 3,000:1, confirmed by SecureTD-Q
Analyte Mass (µg) for 3 repeats using SecureTD-Q
MEK 580 583 580
Benzene 0.14 0.18 0.18
Toluene 94 91 93
Ethyl benzene 30 30 29
PGMEA 43 43 43
Xylene 274 275 271
DMS 28 28 28
Trimethylbenzene 43 44 42
Background:
Stack gases are aggressive matrices requiring a
sampling train to remove particles, acids, etc. The
sample gas is collected onto sorbent tubes using
either grab sampling (using a large gas syringe or a
bellows-type pump to pull a 50-100 ml sample of
stack gas through the tube) or time weighted
average monitoring (using a pump with a slow flow
rate of ~15/ml to pull stack gas through the tube)
throughout a process.
Markes TD systems facilitate quantitative analysis of
high conc. samples (>1000 ppm) by offering the
option of splitting during tube & trap desorption.
Vapour from ppt to high ppm can be accommodated
on one analytical platform. Quantitative re-collection
of both split flows facilitates simple method & data
validation.
Official guidance: Revised European standard prEN
13649
Typical analytical conditions:
Sample volume: 50-1500 ml
Sampling: Pull through tube (grab sampling or pump)
Sorbent: Tenax TA/carbon or carbon/carbon
TD system: Series 2 (U
LTRA-)UNITY or TD-100
Desorption: 5 mins at 330ºC or 280ºC (if TenaxTA)
Trap: Tenax TA/carbon or 2 carbons (-30 to 300ºC)
Split: 3,000:1 double split with SecureTD-Q
Analysis: GC/MS (scan) or GC/FID
Reference: TDTS 77 (stack emissions monitoring)
27
Industrial fence-line (perimeter)
monitoring for fugitive emissions
References: TDTS 49 (fence-line
monitoring), TDTS 1 (list of
diffusive uptake rates for
environmental monitoring) &
TDTS 10 (diffusive sampling in
ambient air)
Hexane
Pentane
Benzene
Heptane
2-week diffusive sampling around a refinery perimeter.
VOCs detected include benzene, toluene & xylene
Toluene
Methylcyclohexane
Background:
Is your industrial site a good neighbour?
Unobtrusive diffusive (passive) samplers may be
placed around a factory fence-line for extended time
periods (e.g. 3-14 days) to monitor key ‘criteria’
pollutants (e.g. benzene & 1,3-butadiene).
Diffusive sampling provides a low cost, well-validated
& quantitative monitoring method. Subsequent
analysis by TD-GC(MS) offers sub-ppb detection
limits. Markes’ TubeTAG technology benefits fugitive
emissions & industrial fence-line studies by making it
easier to record & track sampling locations & other
details. The onboard RFID tag read/write option
available for U
LTRA 2 and TD-100 allows automatic
entry of sample details into the sequence log.
Std. methods: EN 14662-4, EN ISO 16017-2, ASTM
D 6196
Typical analytical conditions:
Sampling: Diffusive (passive) tubes
Sorbent: Carbograph 1TD, Carbopack X or other to
suit target analyte
Xylene
Desorption: 5 mins at 320ºC
TD system: Series 2 (U
LTRA-)UNITY or TD-100
Trap: Selected to suit target analyte (U-T11GPC-2S
in example shown: -30 to 320ºC)
Split: Low split during trap desorption only
Analysis: GC/MS (scan) or GC/FID
28
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Oc
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u
pa
ti
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ygi
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e – mo
perso
Reactive amines in workplace air
Personal exposure to solvents at work
n
a
l
expo
FAN
PNCB
Sulphur dioxide
Acetone
su
re by i
Chloroform
1-chloro-1,3-butadiene
Carbon disulphide
n
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ri
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a
l
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ti
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1PPD
4A
4N
Benzene
Background:
Health & safety at work legislation requires personal
exposure assessment of workers potentially exposed
to toxic chemicals by inhalation. Pumped or diffusive
sampling onto sorbent tubes followed by TD-GC(MS)
analysis provides a solvent-free, safe analytical
option with ~1000x more sensitivity than
conventional charcoal tube/CS2extraction methods.
TD tubes are also reusable indefinitely & may be
RFID tagged (TubeTAG) for enhanced sample
traceability.
Standard methods: UK MDHS series, EN ISO 16017,
ASTM D 6196, NIOSH 2549.
Typical analytical conditions:
Sampling: Diffusive or pumped
Typical tube sorbent: Tenax or Chromosorb
TD system: Series 2 (U
Desorption: 5 mins at 300ºC or 200ºC (for C106)
Trap: U-T2GPH-2S (Tenax/Carbograph 1TD) :-30 to
300ºC
Split: 50:1 to 500:1 (typically double split)
Column: Selected to suit target analyte
range
Analysis: GC/MS (scan)
References: TDTS 37
(industrial air monitoring)
& TDTS 38 (occupational
exposure limit levels)
LTRA-)UNITY or TD-100
®
106
29
Monitoring inhalation exposure
to pesticides
Dichlorvos
Primary & repeat analysis of pesticides for personal exposure
monitoring. Secure TD-Q confirmed quantitative recovery
through the analytical system
Methacrifos
SecureTD-Q:
Repeat analysis
Primary analysis
Diazinon
Etrimfos
Methylchlorpyrifos
Fenitrothion
Phosphamidon
Background:
Agricultural workers involved in pesticide application
must be monitored to ensure that their exposure to
these highly toxic chemicals does not exceed safe
levels. Pumped monitoring using inert (glass or
Chlorpyrifos
Malathion
Methylpirimifos
Silcosteel) tubes together with TD-GC/MS analysis
provides a reliable & highly sensitive monitoring
method.
In the example shown, Markes SecureTD-Q was
used to demonstrate quantitative recovery of these
difficult compounds through the system. SecureTD-Q
can also benefit occupational hygiene applications by
allowing samples to be archived for repeat analysis
under different analytical conditions.
Standard methods: UK MDHS series,
EN ISO 16017-1, ASTM D 6196, NIOSH 2549
Typical analytical conditions:
Sampling: Pumped
Sorbent: Tenax TA in glass or Silcosteel tubes
TD system: Series 2 (U
LTRA-)UNITY or TD-100
Desorption: 10 mins at 280ºC
Trap: U-T9TNX-2S (Tenax TA): -10 to 300ºC
Split: ~10:1 during trap desorption only
Analysis: GC/MS (SIM)
Reference: TDTS 39 (using TD with SecureTD-Q
to monitor vapour phase pesticides)
30
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The advantages of TD vs. solvent
extraction for monitoring organic
vapours in air
Background:
Early methods for monitoring vapour-phase organics
in air involved charcoal tubes & solvent extraction,
typically with CS
occupational limit levels & widespread adoption of
GC/MS technology, thermal desorption is rapidly
superseding solvent extraction as the analytical
method of choice.
Key advantages of thermal desorption vs.
charcoal/CS2methods include:
• 1000 fold enhancement in sensitivity
• Reliable (>95%) desorption efficiency
• Higher degree of automation and greatly reduced
running costs
• Elimination of the danger and expense associated
with hazardous solvents and their disposal
• Reduced analytical interference
• Reusable sample tubes
Furthermore, Markes’ introduction of SecureTD-Q
now means TD is no longer a one-shot technique.
Samples can be quantitatively re-collected for repeat
analysis.
References: TDTS 38 (workplace limit levels) &
TDTS 46 (comparing TD with CS
charcoal for air monitoring)
. However, with the lowering of
2
extraction of
2
31
Diffusive (passive) sampling in
the workplace
Standard sorbent tube fitted with a diffusion cap at the sampling
(grooved) end
Background:
Unobtrusive, low-cost diffusive (passive) samplers
facilitate personal exposure monitoring because they
can be worn close to the breathing zone without
impacting worker behaviour. Analysis by thermal
desorption means tubes are reusable indefinitely.
The enhanced sensitivity of TD, relative to solvent
extraction, also allows compliance with new, lower
threshold limit values.
Diffusive sampling tubes can be fitted with Markes
TubeTAG RFID tagging technology to simplify logging
& tracking of key sample-related information
Std. methods: UK MDHS series, EN ISO 16017,
ASTM D 6196, NIOSH 2549
Typical analytical conditions:
Sorbent: Tenax TA, Carbograph 1TD or porous
polymer sorbent (various)
TD system: Series 2 (U
LTRA-)UNITY or TD-100
Desorption: 5-10 mins. Temp depends on sorbent
Trap: U-T2GPH-2S (General purpose)
Split: Between 10:1 & 500:1
Analysis: GC(MS)
References: TDTS 01 (diffusive uptake rates), TDTS
08 (principles of diffusive sampling), TDTS 38
(limit levels) & TDTS 50 (workplace air monitoring)
32
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Biological monitoring via alveolar breath
2-butanone
Acetone
Toluene
1-methyoxy-2-propanol
Skin-absorbed solvents in the breath of shoe workers collected
using the Bio-VOC™
Chromatogram of a clinical breath sample.
Sample collected using the Bio-VOC and analysed using
TD-GC/MS (single ion monitoring at mass 43)
Reproduced by kind permission from Pyschiatric Diagnostics Ltd., Inverness, Scotland
Xylene
Background:
Biological exposure monitoring allows assessment of
the whole body burden of chemicals via all routes of
exposure (skin absorption, ingestion & inhalation).
Alveolar breath sampling using Markes’ disposable
Bio-VOC™ allows large-scale, non-invasive biological
monitoring of workers using personal protective
equipment (PPE) or handling skin-absorbed
chemicals.
Detection of specific VOCs/VOC profiles in breath can
also be used to monitor halitosis or help diagnose
certain diseases (e.g. lung cancer & diabetes).
After breath collection, the Bio-VOC breath sample is
discharged into a tube containing hydrophobic
sorbents & analysed by TD-GC/MS.
Official guidance: Suite of breath sampling guidance
notes available from UK HSL.
Typical analytical conditions:
Sorbent: Tenax TA or Tenax/Carbopack X
TD system: Series 2 (U
LTRA-)UNITY or TD-100
Desorption: 5 mins at 280ºC
Trap: Tenax TA or Tenax/Carbopack X (25-280ºC)
Splitless or low split
Analysis: GC/MS (SIM) or
GCxGC/TOF MS
References: TDTS 13, TDTS 48
& TDTS 18
33
The Markes International advantage
Markes is the world leader in analytical thermal
desorption and has pioneered important technical
innovations such as SecureTD-Q (quantitative sample
re-collection for repeat analysis), TubeTAG electronic
labels for sorbent tubes and universal (multi-application)
heated valve technology.
Markes leadership in TD now extends to:
• The widest available product portfolio and
application range
• Product quality and reliability
• Excellence in technical and applications support
Trademarks
UNITY™, ULTRA™, Air Server™, CIA 8™, TD-100™, µ-CTE™, SafeLok™,
DiffLok™, VOC-Mole™, Bio-VOC™, TT24-7™, TC-20™, TD-100™, UniCarb™,
TubeTAG™ & SecureTD-Q™ are trademarks of Markes International Ltd, UK
®
is a registered trademark of Buchem B.V., Netherlands
Tenax
Carbograph™ is a trademark of LARA s.r.l., Italy
Carbopack™ is a trademark of Supelco Inc., USA
®
Silcosteel
Chromosorb
Nafion
Wilmington, DE, USA
GS-GasPro™ is a trademark of Agilent Technologies, Inc, Santa Clara, CA, USA
is a registered trademark of Restek Inc., USA
®
is a trademark of Manville Corp., USA
®
is a registered trademark of E.I. du Pont de Nemours & Company,
For more information on Markes comprehensive range of
thermal desorption instruments and sampling accessories
request your free copy of Markes TD Accessories and
Consumables catalogue
34
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E: enquiries@markes.com W: www.markes.com
Markes International Ltd
Gwaun Elai Medi Science Campus
Llantrisant
RCT
CF72 8XL
United Kingdom
T: +44 (0)1443 230935 F: +44 (0)1443 231531
E: enquiries@markes.com W: www.markes.com
www.markes.com
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