MARKES Thermal Desorption Applications Guide

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)

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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