Monitoring trace VOCs

in humid air
Novel water management solutions
for thermal desorption
Unparalleled expertise in air monitoring
Global regulations with expanding target lists are driving a need for more versatile air monitoring tools –
a need that is met by thermal desorption (TD) with GC–MS.

Air streams monitored using tubes, canisters or by on-line methods frequently contain high levels of
water vapour. However, moisture can lower sensitivity, cause poor chromatography (peak shape and
repeatability), and reduce column and detector lifetime.

Removing water without using liquid cryogen is essential to achieve good results and minimise the
running and maintenance costs of the entire analytical system.

With 20 years at the forefront of TD innovation and applications development,

Markes International can recommend the three best solutions for water
management:
■■ Kori-xr water condenser for canister and on-line monitoring.
■■ Nafion dryer for routine on-line air monitoring with conventional GC detectors.
■■ Dry-purging of sorbent tubes and traps (standard in every TD system).

Markes ‘xr’ series of thermal desorbers offers outstanding versatility for the
monitoring of volatile and semi-volatile organic compounds (VOCs and SVOCs) in
air streams:
■■ Extended analytical range – from C2 to C44, including reactive and thermally
labile species.
■■ Extended re-collection capability, available for tubes, canisters and on-line.
■■ Extended reliability.
Water management options
Selecting the best approach for your application

The three complementary water management solutions offered by Markes enable users to
optimise their TD system for each application challenge. Whatever the target compounds,
analyte level or sampling method, one or more of these options will guarantee best possible
performance across a wide range of sample humidities.

Non- Polar Mono-

Description Key features C2 Typical applications
polar C3 VOCs terpenes

Canister or on-line monitoring of:

■■ Cryogen-free
trap placed before sorbent trap
■■ VOCsand VVOCs (US EPA Method
enables water to be removed from the sample.
Kori-xr
■■ No loss of polar and non-polar compounds.     TO-15, PAMS Method or Chinese EPA
Method HJ 759).
■■ Ideal for GC–MS analysis of complex air samples. ■■ Oxygenates (OVOCs).

■■ Hydrophilicco-polymer widely used for the Canister or on-line monitoring of:

analysis of C2–C10 ozone precursors. ■■ Ozone precursors (PAMS Method).
Nafion
dryer
■■ PolarVOCs and monoterpenes are purged along
with the water.
  × × ■■ VOCsand VVOCs (Chinese EPA
Method HJ 759).
■■ Ideal for GC–FID analysis of VOCs. ■■ Hazardous air pollutants.

Tube, canister or on-line monitoring of:

■■ Selection
of appropriate sorbent materials and ■■ VOCsand SVOCs (US EPA Methods
trap temperature eliminates most of the water. TO-15 and TO-17).
Dry-purging ■■ Very
volatile species cannot be trapped under
these conditions.
×    ■■ Fenceline
325).
emissions (US EPA Method

■■ No additional hardware needed. ■■ Stack

emissions (CEN/TS 13649 or
Chinese EPA Method HJ 734).
Kori-xr ™
High-performance water removal

Markes’ new water management device, Kori-xr, delivers outstanding results for on-line and canister analysis
of humid air by TD–GC–MS without any need for liquid cryogen. The efficient removal of water by Kori-xr
permits lower temperatures to be used in the focusing trap without risk of ice formation, allowing quantitative
retention of VOCs, VVOCs, oxygenates and monoterpenes on the UNITY-xr ™ thermal desorber.

How Kori-xr works

GC
To
1 Air sampling and water removal: 2 Trap desorption and water purging:
The Kori-xr trap, held at –30°C, sits in-between the When sampling is complete, the analytes are
sample inlet and the sorbent-packed focusing transferred from the focusing trap to the
trap, causing vapour‑phase water ( ) in the GC, and ice is purged from the

p
air sample to be deposited as ice. Kori-xr trap, to prepare it for the
ra
rt Kori-xr was developed
i -x
During this process, collection of next sample.

p
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Ko

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in collaboration with
VOCs ( ) on the

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the National Centre for

us
focusing trap continues Atmospheric Science (NCAS)

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unaffected. at the University of York. It was
co-funded by the UK’s innovation
agency (Innovate UK), the Natural
Environment Research Council (NERC)
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m

and the Welsh Government under the

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Knowledge Transfer Partnership program.

Monitoring TO-15 compounds in humid air

When should I choose Kori-xr?
1 Ethanol 5 Vinyl acetate
2 Acrolein 6 Butan-2-one
• When you need to analyse polar and non-polar VOCs and 3 Acetone 7 Ethyl acetate
Using Kori-xr and Markes’
2
Abundance (× 105 counts)

4 Isopropanol 8 Tetrahydrofuran UNITY–CIA Advantage-xr ™

VVOCs by GC–MS.
5 system to analyse humid
• When your sample has high relative humidity. air allows interference-free
monitoring of polar and
• When you need to reliably quantify compounds from 8 non-polar compounds cited
1 7
C2 to C12. 3
6 in US EPA Method TO-15 for
4 canister sampling and
• When you need to reach very low MDLs. 1 2
analysis.
• When you need to fully characterise unknown atmospheres. 6 8 10 12
Time (min)
Improved retention of ultra-volatile and polar species

Nafion dryer
Detected Response Kori-xr Kori-xr shows
Detected
Compound using Nafion linearity (R2) enhanced
using Kori-xr?
dryer? using Kori-xr recovery of

Response (× 108 counts)

4 low-boiling and
Ethanol ×  0.973 polar VOCs from
an air stream with
Acetone   0.993
80% RH,
Toluene-d8 (I.S.)   1.000
2
compared to use
of a Nafion dryer.
Ethylbenzene   0.999

α-Pinene ×  0.999

β-Pinene ×  0.997
0
1,2,4-Trimethylbenzene   0.999

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1,
Strong responses from highly polar compounds

Ethanol Acetone Ethanol and acetone

4 are scarcely visible
in this 80% RH air
1 stream when it is

Response (× 108 counts)

Response (× 107 counts)

3 monitored using a
Nafion dryer. In
Kori-xr Kori-xr contrast, Kori-xr
allows quantitative
2 analysis of these
important polar
compounds.
1 Nafion dryer Nafion dryer

0 0
5.9 6.0 6.1 6.2 6.3 6.6 6.7 6.8 6.9 7.0
Time (min) Time (min)
Nafion ™ dryer
Efficient membrane-based water removal

Membranes constructed of hydrophilic co-polymers such as Nafion are widely used to remove water from humid air streams,
especially for the analysis of C2–C10 hydrocarbons, known as ‘ozone precursors’. However, many polar VOCs (such as alcohols,
aldehydes, ketones, esters and glycol ethers) plus key monoterpenes (such as α- and β-pinene) also migrate through the
membrane. This can be a major advantage for routine air monitoring applications carried out using Markes’ UNITY–Air Server-xr ™
with conventional GC detection – enabling confident analysis of target compounds with minimal interference from unknowns.

How Nafion dryers work

1 Air sampling: 2 Water removal:

The air sample containing Water in the air stream is adsorbed onto the polymer surface
water ( ) and VOCs ( ) and, driven by the humidity gradient, passes through to be
passes through a Nafion removed by a stream of purge gas. However, the presence of
polymer tube before reaching strongly acidic groups on the polymer surface means that

To trap
e

the sorbent-packed some polar compounds also migrate through.

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fo c
m

focusing trap.
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us
in g
Reliable analysis of ozone precursors 1
2
Ethane
Ethene
16
17
2-Methylpentane
Isoprene
When should I choose 25 3 Propane 18 n-Hexane
16 17 26 4 Propene 19 Benzene
Nafion dryers? 23 24
27 28
5 2-Methylpropane 20 2,2,4-Trimethylpentane
6 n-Butane 21 n-Heptane
14 18 7 Acetylene 22 Toluene
• When you are not 1112 15
20 29
22 8 trans-But-2-ene 23 n-Octane
9 21
interested in analysis 9 But-1-ene 24 Ethylbenzene
6 8 10 30 10 cis-But-2-ene 25 m-/p-Xylene
of polar compounds. 13
19
11 2-Methylbutane 26
5 12 n-Pentane 27 o-Xylene
• When you run VOC 13 Butadiene 28 1,3,5-Trimethylbenzene
4 14 trans-Pent-2-ene 29 1,2,4-Trimethylbenzene
analysis by GC–FID. 15 Pent-1-ene 30 1,2,3-Trimethylbenzene

• When you need an 1

3
2 7
affordable and Using a Nafion dryer allows interference-free
analysis of ozone precursors using a dual-
reliable solution for
column setup and GC–FID, at levels well below
sulfur compounds. 10 15 20 25 30 35 20 25 30 35 40 the 0.5 ppb required for the PAMS Method.
Time (min)
Dry-purging
The built-in option for water removal

Dry-purging is a powerful and versatile tool for selectively eliminating water and other unwanted interferences prior to air analysis.
It harnesses the sorbent selection expertise and precise temperature control available with Markes’ instruments, and can be
applied to all air sampling methods – sorbent tubes, canisters, bags and on-line air monitoring. However, a drawback of this
approach is that C2 hydrocarbons are not quantitatively retained by the focusing trap, and therefore cannot be reliably reported.

How trap dry-purging works

e
pl

GC
m

To
Sa
1 Sample trapping:
The air sample containing water ( ) and VOCs ( ) is drawn onto the
sorbent-packed focusing trap, which is usually held at 25°C.
1 3

p
tr a
2 Water removal:

g
in
us
Water is purged from the trap with dry carrier gas in the

c
Fo
sampling direction.

3 Trap desorption:
The flow of carrier gas is then reversed and
the trap heated rapidly in the usual way, to
desorb the analytes.
2

Analysis of humid stack emissions

When should I choose dry‑purging? 4
1 Isopropanol
6 Use of tube and trap dry-
Abundance (× 108 counts)

• When your analyte range is C3–C44. 2

3
Benzene
Toluene purging gives excellent results
5
• When you need compatibility with 4
4 m-/p-Xylene 3 for tubes containing the CEN/
5 1-Dodecene
TS 13649 standard at 100 ng
tube (passive and pumped), on-line per analyte.
and canister analysis. 2 2
1
• When you would prefer not to use
0
additional hardware. 4 6 8 10 12
Time (min)
 L-0075 (080618-6)
Product names used with the ™ symbol are trademarks of Markes International, with the exception of Nafion™, which is a trademark of the Chemours Company.
Markes International – The TD experts
World-leading instruments and unmatched expertise in VOC and SVOC monitoring

Markes International has for 20 years been at the forefront of innovation for enhancing the measurement of trace-level VOCs and SVOCs by thermal desorption–
gas chromatography. Our suite of instruments for thermal desorption sets the benchmark for quality and reliability:

TD100-xr ™ UNITY-xr ™ UNITY–Air Server-xr™ ULTRA-xr ™ CIA Advantage-xr ™ TT24-7™

High-throughput Single-tube thermal Versatile on-line VOC High-throughput Cryogen-free Twin-trap instrument
100-tube automated desorber featuring monitoring system. 100-tube automated canister for near-real-time
thermal desorber. sample re-collection autosampler for autosampler and on-line monitoring.
of all split flows. UNITY-xr. pre-concentrator.

Markes International
UK: Gwaun Elai Medi-Science Campus, Llantrisant, RCT, CF72 8XL T: +44 (0)1443 230935
USA: 2355 Gold Meadow Way, Gold River, Sacramento, California 95670 T: +1 866-483-5684 (toll-free)
Germany: Bieberer Straße 1–7, 63065 Offenbach am Main T: +49 (0)69 6681089-10
P.R. China: No. 1 Building, No. 7 Guiqing Road, Xuhui District, Shanghai 200233 T: +86 21 5465 1216

E: enquiries@markes.com W: www.markes.com