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Thermal Desorption: A Practical Applications Guide

I. Environmental Air Monitoring andOccupational Health & Safety w

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Introduction to MarkesInternational Ltd.

Formed in 1997, Markes International Ltd. is one ofthe world’s leading suppliers of thermal desorption(TD) equipment for monitoring trace toxic andodorous chemicals in air, gas and materials. Servingfast growing markets from environmental health andsafety to materials testing and from food / flavour /fragrance to defence / forensic, Markes’ globalcustomer base includes major industry, governmentagencies, academia and the service laboratory sector.

Markes has introduced several highly successfulbrands of TD instruments to the market including:UNITY™ – a universal TD platform for single tubes,the 100-tube ULTRA™ TD autosampler, theAir Server™ interface for canisters and on-linesampling, the µ-CTE™ Micro-Chamber / ThermalExtractor for materials testing, the TT24-7™ forcontinuous on-line monitoring and the TC-20™ multi-tube conditioner.

Markes also supplies a wide range of samplingaccessories and consumables for all TD applicationareas.

What is TD?

Since the early 1980s, thermal desorption hasprovided the ultimate versatile sampleintroduction technology for GC / GC-MS. Itcombines selective concentration enhancementwith direct extraction into the carrier gas andefficient transfer / injection all in one fullyautomated and labour-saving package.

Markes International Ltd. UK headquarters

ApplicationsThermal desorption is now recognised as thetechnique of choice for environmental air monitoringand occupational health & safety. Relevant standardmethods include: ISO/EN 16017, EN 14662 (parts 1& 4), ASTM D6196, US EPA TO-17 and NIOSH 2549.Related applications include monitoring chemicalwarfare agents (CWA) in demilitarisation / destructionfacilities & civilian locations (counter-terrorism).

TD is also routinely used for monitoring volatile andsemi-volatile organic compounds (S)VOCs in productsand materials. Examples include residual solvents inpackaging & pharmaceuticals, materials emissionstesting and food / flavour / fragrance profiling.

This publication presents several real worldapplications in environmental air monitoring andoccupational health & safety. Accompanyingpublications cover the application areas of:

• Food, flavour, fragrance & odour profiling

• Defence & forensic

• Emissions from products and materials

Environmental air monitoring• Atmospheric research

• Ambient / urban air monitoring

• Industrial (stack) emissions

• Odour components

• Indoor air quality

Occupational health & safety• Personal exposure monitoring (inhalation)

• Biological exposure assessment (breathtesting)

Markes International Ltd.T: +44 (0)1443 230935 F: +44 (0)1443 231531E: [email protected] W: www.markes.com

Typical analytes of interest:• Freons

• Volatile aromatics such as benzene

• C2 - C10 hydrocarbons

• Nitrates

Concentrations: ppt levels

Atmospheric research Background:Thermal desorption is used extensively inatmospheric research for monitoring trace organicvapours. For example:

• Global migration of pollution

• Research into stratospheric chemistry

• Marine research – studying the oceans as apotential ‘sink’ or reservoir for air pollutants

• Historical pollution data – e.g. levels of freonsin air bubbles trapped in polar ice

Std. methods: EN ISO 16017-1, ASTM D 6196, USEPA TO-17, (tubes) or US EPA TO-15 (canisters)

Typical TD-GC conditions:Sampling: Pumped multi-sorbent tube or canister

TD: ULTRA-UNITY or UNITY-Air Server (+dryer)

Dry purge if no dryer used during sampling

Splitless desorption

Trap: Air Toxics / water m’gement: -15 to 320ºC

Analysis by GC-MS using SIM or NCI

Reference: TDTS17 UNITY detection limits,TDTS31 UNITY system performance

30 ml of air from bubbles in the ice core collected incanisters. Analysis by TD-GC-MS in NCI mode. Unit ppt

detection limits

Ions: 3579127

Typical analytes:• Freons & other halogenated hydrocarbons

• Volatile aromatics

• Oxygenates

Concentrations: ppt levels

Background:SafeLok samplers have the same capacity asstandard tubes but incorporate Markes’ patented*

diffusion-locking (DiffLok™) technology at bothends of the tube to prevent artifact ingress.

With the same external dimensions as standardTD tubes, SafeLok tubes are ideal for monitoringultra-low concentration environments – forexample at the North Pole or in mid-Pacific.Samples are protected from contaminationduring storage / transport and duringsubsequent TD-GC-MS analysis in a conventionallaboratory.

Std methods: EN ISO 16017-1, US EPA TO-17,ASTM D 6196

Typical TD-GC conditions:Sampling: Pumped multi-sorbent SafeLok tube

TD: ULTRA-UNITY

Dry purge


Trap: Air Toxics / water m’gment: -15 to 320ºC

Analysis by GC-MS using SIM or NCI

Reference: TDTS61 on diffusion lockingtechnology, Markes SafeLok tubes leaflet

SafeLok™ – Specialist sampletubes for trace detection

Threaded DiffLokinserts protect bothends of the sorbenttube

SafeLok samplers incorporate Markes’ patented*DiffLok technology to prevent artifact ingress. This

aids trace level monitoring

* GB 2337513US 6,564,656 B1


Typical analytes:• Volatile aromatics

• 1,3-butadiene

Concentrations: Sub to low ppb levels

Criteria pollutants in ambientair by diffusive sampling

Background:Accurate mapping of pollution levels across amajor urban centre requires hundreds of samplingpoints. Diffusive samplers, combined withautomated TD-GC(-MS) analysis, provide anaffordable and easily deployed monitoring option.

Std. methods: EN 14662-4, EN ISO 16017-2,ASTM D 6196

Typical TD-GC analytical conditions:Sampling: Diffusive (passive)

Sorbent: Carbograph 1TD™ (benzene),

Sorbent: Carbopack X™ (1,3-butadiene)

Monitoring time: 7-14 days (axial), 4-6 hours(radial)

Desorption: 5-10 minutes at 320ºC

Trap: C’graph 1TD / Carb X from +30 to 320ºC

Split: ~20:1 during trap desorption only

Analysis by GC-FID or GC-MS

Reference: TDTS10 on diffusive monitoring ofambient air, TDTS01 on uptake rates, TDTS42on radial diffusion for TD

Rouen (Northern France)Interpolated benzene isoconcentration plot

Measurements performed from 19-23/01/98

Typical analytes:Hydrocarbons, halogenated hydrocarbons, CS2,volatile aromatics, ketones, esters & other odorous /toxic VOCs ranging in volatility from freons tohexachlorobutadiene


TO-17 ‘Air Toxics’ in urban airusing pumped sorbent tubes

Background:US Clean Air Act regulations have identifiedspecific ‘Hazardous Air Pollutants’ (HAPs) alsoknown as ‘Air Toxics’. These analytes cover a widerange of polarities & volatilities and are mosteffectively monitored using pumped sampling ontomulti-sorbent tubes / traps with automatedTD-GC-MS(SCAN) analysis.

Std. method: US EPA Method TO-17

Typical TD-GC analytical conditions:Sampling: Pumped sorbent tube

Sorbent: Dual-sorbent – e.g. ‘Air Toxics’ tube

TD system: ULTRA-UNITY

On- or off-line dry purge before desorption

Desorption: 10 mins at 320ºC

Trap: Air Toxics trap: +30 to 330ºC

Split: Low split during trap desorption only

Analysis: GC-MS(SCAN)

Reference: Markes Technical SupportDocument for TO-17, TDTS27 on samplingmethods for VOCs in air

Active sampling of volatiles in ambient air usingsorbent tubes / traps


CO

S

HC

C2H

2F 4

CH

3Cl

HCC

HClF

2CCL 2

F 2

CH

3Br

SO

2

CS

2

Freo

n 1

13

Met

hyl

ene

Chlo

ride

HC

Oxy

gen

ated

HC

CCl 3

F

Ben

zene

1,1

,1-t

rich

loro

ethan

e

Tric

hlo

roet

hyl

ene

CCl 4

C2Cl 4

Tolu

ene

Dim

ethyl

Sulp

hid

e

Background:While sorbent tubes provide the most cost-effective and versatile sampling solution for VOCAir Toxics, passivated and evacuated canisters canalso be used for ‘grab’ sampling ambient air.Subsequent analysis is by TD-GC-MS(SCAN). Veryvolatile apolar VOCs are quantitatively recoveredfrom the canisters, however, polar and less volatilecompounds may be lost due to condensation oninner surfaces.

Std. method: US EPA Method TO-15 (formerlyTO-14)

Typical TD-GC analytical conditions:Sampling: Evacuated canister

TD system: UNITY-Air Server (no dryer)

Trap: Air Toxics trap: +30 to 330ºC

Dry purge of cold trap before desorption



Reference: TDTS27 on sampling methods forVOCs in air

TO-15 ‘Air Toxics’ in urban airusing canisters

Typical analytes:Hydrocarbons, halogenated hydrocarbons, CS2,volatile aromatics, esters & other odorous / toxicVOCs ranging in volatility from freons tohexachlorobutadiene


Repeat analysis of TO-14 / 15 canister standard usingUNITY-Air Server (up to 8 channels)

Typical analytes:Hydrocarbons ranging in volatility from ethane,ethene and ethyne (acetylene) to trimethyl benzene


‘Ozone precursors’ (C2 to C10hydrocarbons) in ambient air

Background:C2 to C10 hydrocarbons, primarily from carexhausts, have been identified as precursors tothe formation of street level ozone and urbansmog. US, European and other regulators requireround-the-clock monitoring of these compounds inmajor urban centres during the summer months.UNITY-Air Server allows continuous, unattendedand cryogen-free monitoring at low to sub ppblevels. Chromatographic data, from multiplestations, are accessed via telemetry and processed/ validated at remote network control centres.

Official guidance: US EPA Tech. Assist. Documentfor sampling and analysis of ozone precursors

Typical TD-GC analytical conditions:Sampling: On-line from manifold at 10-15 ml/min

Sampling volume: ~400 ml

TD system: UNITY-Air Server (with dryer)

Trap: Ozone Precusor trap: -15 to 320ºC


Analysis: GC, dual column, dual FID & Deans switch

Reference: TDTS16 On-line monitoring ofozone precursors in ambient air

Splitless desorption of 56-compound US EPA mix ofozone precursors using UNITY-Air Server with dual

column / dual FID GC with Deans switch

PLOT column

BP1 column


Background:Polyaromatic hydrocarbons (PAH) are toxic semi-volatile organic compounds present in ambient airin both particulate and vapour form. Fast(~500 ml/min) pumped sampling of the vapourfraction onto tubes packed with a combination ofquartz wool and carbon sorbents followed by TD-GC-MS analysis allows measurement of PAH at lowppt levels.


Sorbent: Quartz wool with 1 or 2 carbon blacks

Sample volume: ~100 L at 500 ml/min



Trap: High boilers trap: -10 to 350ºC

Split: Typically 30:3 during trap desorption only

Analysis: GC-MS(SIM)

Reference: M. Caputi, ‘Monitoring of VOCsand PAHs in the atmosphere’, PhD thesis2004, TDTS53 on quantitative recovery ofsemi-volatiles with Markes (ULTRA-)UNITY TDsystems

Vapour-phase PAH by TD

Analytes shown:1: naphthalene 9: benz(a)anthracene2: acenaphthylene 10: chrysene3: acenaphthene 11: benzo(b)fluoranthene4: fluorene 12: benzo(k)fluoranthene5: phenanthrene 13: benzo(a)pyrene6: anthracene 14: dibenz(a,h)anthracene7: fluoranthene 15: benzo(g,h,i)perylene8: pyrene 16: indeno(1,2,3-cd)pyrene

Semi-volatile PAHs are quantitatively recovered usinga Markes ULTRA-UNITY TD system

1

16

15

14

13

12

11

10

987

654

32

Typical analytes:Isoprene, monoterpenes (α-pinene, limonene, etc.),sulphur compounds, ketones

Concentrations: 0.1 to 100 ppb

Biogenic emissions - VOCsfrom moulds, plants, etc.

Background:Plants, moulds, animals and other life forms emitVOCs and contribute to the ‘cocktail’ of organicvapours in ambient air. Monoterpenes, for example,are emitted by pine trees on sunny days, possiblyas a defence against potential photochemicaldamage. These reactive hydrocarbons aremonitored using pumped sampling onto inert,Tenax tubes followed by TD-GC-MS analysis.Mould emissions of methyl benzoate are monitoredin indoor air using a similar method.

Std. methods: EN ISO 16017-1, ASTM D 6196


Sorbent: Tenax TA™ in stainless / Silcosteel™ tube



Trap: Tenax trap: -10 to 250ºC



Reference: J. Kristensson et al., ‘Sampling &analysis of atmospheric monoterpenes’, Deptof Meteology, Stockholm University, 1991

Terpenes from leaf litter

Monoterpenes & terpenoids

Sesquiterpenes

Terpenoids


Industrial (stack) emissions -solvents

Background:Stack gases are aggressive matrices requiring asampling train to remove particles, acids etc. Theresultant air is either pulled through a TD tube usinga gas syringe (grab sampling) or pumped onto atube at low flow rates (time weighted average).Analysis by TD-GC(-MS) using a high (double) splitratio, allows fast, solvent-free quantification of highVOC concentrations. Mi SecureTD-Q (re-collectionfor repeat analysis) validates quantitative data.

Official guidance: UK Env Agency docs M2, S4.01, S4.02

Typical TD-GC analytical conditions:Sample volume: 100-1500 ml

Sampling: Pull through tube (gas syringe / lowflow pump)

Sorbent: Tenax / carbon or carbon / carbon


Desorption: 5 mins at 330ºC or 280ºC (if Tenax)

Trap: Tenax / carbon or 2 carbons 30 to 300ºC

Split: 3,000:1 double split with SecureTD-Q

Analysis: GC-MS(SCAN) or GC-FID

Reference: TDTS77 on stack emissionsmonitoring

Quantitative stack analysis confirmed by SecureTD-Q

Analyte Mass in µg for 3 repeats

MEK 580 583 580Benzene 0.14 0.18 0.18Toluene 94 91 93

Ethyl benzene 30 30 29PGMEA 43 43 43Xylene 274 275 271DMS 28 28 28

Trimethylbenzene 43 44 42

Second re-collectedsample

First re-collectedsample

Original sample

Vapour-phase semi-volatiles byThermal Desorption

Background:Thermal desorption is usually associated withanalysis of volatile organic chemicals. However,the short, inert, heated flow path of Markes TDsystems also ensures quantitative recovery ofsemi-volatiles up to n-C40.


Sorbent: Quartz wool with 1 or 2 carbon blacks

Sample volume: ~100 L at 500 ml/min



Trap: High boilers trap: -10 to 350ºC

Split: Typically 50:2.5 during trap desorption only


Reference: TDTS53 on quantitative recoveryof semi-volatiles with Markes (ULTRA-)UNITYTD systems

Typical analytes:• Polychlorinated biphenyls (PCBs)

• Polyaromatic hydrocarbons (PAHs)

• Plasticisers such as phthalates

• Hydrocarbons from diesel emissions

Complete recovery of n-C40 through Markes UNITY TD


C18

C20

C24

C26

C32

C36

C40

Typical analytes:• CS2

• H2S (NB: requires special focusing trap)

• Mercaptans (thiols)

• Sulphides

Concentrations: Sub to low ppb

Odorous industrial emissions Background:Highly odorous sulphur compounds in industrial orlandfill emissions must be controlled to sub or low-ppb levels. These very volatile and highly reactivecompounds are usually sampled on-line or incanisters / bags and analysed using TD-GC-FPD.

Std. method: Korean Government GuidanceMethod - Standard Method for Off-Odour Analysis(2005)


TD system: UNITY-Air Server (+ dryer)

TD flowpath: 80ºC

Trap: Sulphur trap or H2S trap -15 to 250ºC

Split: 5:1

Analysis: GC-FPD

Reference: TDTS32 onanalysis of sulphurcompounds

Reduced sulphur compounds via UNITY-Air Server

H2S

Met

hyl

mer

capta

n

Eth

yl m

erca

pta

nD

imet

hyl

sulp

hid

e

CS

2

Dim

ethyl

dis

ulp

hid

e

Typical analytes:Freons such as CF4, C2F6 and C3F8

Concentrations: Low mg/m3

Stack emissions of freons Background:Highly volatile freons are emitted by aluminiumsmelting and industrial halogenation processes.Freons are known to damage the protective ozonelayer in the higher atmosphere and their emissionsare rigorously controlled. With a bpt. of -169ºC,CF4 is extremely difficult to trap, but sampling intobags / cans combined with TD-GC-MS or ECDanalysis of small volumes of the gas allowscryogen free monitoring at low levels.

Typical TD-GC analytical conditions:Sampling: On-line or whole air / gas containers

TD system: UNITY-Air Server

Trap: Carbon molecular sieve -15 to 320ºC

Low split during both tube and trap desorption

Analysis: GC-MS or GC-ECD

Note that TD-GC-MS (SCAN)was used in the exampleshown

30 ml volumes of freon standard showing quantitativetrapping of CF4 without liquid cryogen


80 mg/m3

mixed std

300 mg/m3 std ofCF4 & C2F6 only

Typical analytes:• Benzene

• 1,3-butadiene

• Mixed solvents and hydrocarbons

Concentrations: ppb to ppm

Industrial fence-line monitoring Background:Is your industry a good neighbour? Unobtrusivediffusive (passive) samplers may be placed arounda factory fence-line for extended time periods –e.g. 3 to 14 days. When combined withsubsequent automated TD-GC(-MS) analysis, thisprovides a low cost and reliable method formonitoring perimeter concentrations at ppb-ppmlevels.

Std. methods: EN 14662-4, EN ISO 16017-2,ASTM D 6196

Typical TD-GC analytical conditions:Sampling: Diffusive (passive) tubes

Sorbent: Carbograph 1TD, Carbopack X or other



Trap: Dual carbon black -10 to 320ºC



Reference: TDTS49 on fence-line monitoring

2-week diffusive sampling around a refinery perimeter.VOCs detected include benzene, toluene & xylene

Xyl

ene

Tolu

ene

Hep

tane

Met

hyl

cycl

ohex

ane

Ben

zeneHex

ane

Penta

ne

Typical analytes:• Hydrocarbons from fossil fuels

• Halogenated solvents

Concentrations: 1 to 100 ppm

In-situ monitoring ofunderground fuel leaks

Background:Underground fuel or chemical leaks present agrave environmental risk. Soil probes containingstandard diffusive tube samplers allow cost-effective, in-situ screening of large areas of landincluding active production sites. They can also beplaced along the length of fuel pipelines to provideearly warning of a leak. Diffusive tubes inside thesoil probes monitor the soil gases for ~24 hours.Automated TD-GC analysis allows rapididentification of the nature, source and spread ofground contamination.

Typical TD-GC analytical conditions:Sampling: Diffusive tubes inside soil probes

Sorbent: Tenax TA



Trap: Tenax TA or dual bed -10 to 300ºC

Split: Double split


Reference: TDTS29 on monitoring soilpollution using soil probes

VOC-Mole™ Soil Probes arranged in a grid patternaround an industrial site allow low-cost mapping of

contaminated ground


Target compounds include:Chloroethane, VCM, benzene, 2-butoxy ethanol,1,1-dichloroethane, trichloroethene, tetrachloromethane,1,1-dichloroethene, 1,2-dichloroethene, CS2, methanethiol,butyric acid, ethyl butyrate, 1-propanethiol, dimethyldisulphide, ethanethiol, 1-pentene, 1-butanethiol, dimethylsulphide, 1,3-butadiene, furan

Concentrations: 10 to 100 ppb

Odours and toxics in landfill gas Background:New EU regulations require monitoring of tracetoxic and odorous compounds in landfill gas. 100-200 ml samples are drawn through a specialsorbent tube using a gas syringe. Subsequentgentle desorption on an inert ULTRA-UNITY TD setat low (<100ºC) flow path temperatures allowsmeasurement of trace target analytes includingthiols.

Official guidance: UK Env. Agency publication‘Monitoring trace components in landfill gas.’


Silcosteel tube with Tenax TA / UniCarb™


TD flowpath: 120ºC

Trap: Sulphur trap -15 to 220ºC (40º/min)

Split: From 10:1 to 50:1


Reference: TDTS47 andTDTS74 on analysis oflandfill gas

100 ml landfill gas with trace target analytes andmany major components identified

Redesorption blank

Vin

yl c

hlo

ride

Chlo

roet

han

e

1-p

ente

ne

1,1

,1-t

rich

loro

ethan

e

1,1

- &

1,2

-dic

hlo

roet

hen

eButa

n-2

-ol

1,1

-dic

hlo

roet

han

e

Car

bon d

isulp

hid

eD

imet

hyl

sulp

hid

eFu

ran

Dim

ethyl

dis

ulp

hid

e

Tric

hlo

roet

hen

e

Ben

zene

Buta

n-1

-ol

Buta

noic

aci

d e

thyl

est

er

Xyl

ene

Tolu

ene

Nonan

e

Lim

onen

e

Dec

ane

α-p

inen

e

Typical analytes:Almost any VOC or (S)VOC

Concentrations: Sub to low ppb levels[Note that in this example detection limits are in theorder of 10-50 ppt.]

Profiling indoor air quality Background:TD is used extensively for monitoring indoor airquality and for related applications such asevaluating emissions from building materials. Inthis example, pumped tube samplers were usedwith subsequent TD-GC-MS analysis for profiling ofppt-ppb level VOCs.

Std. methods: US EPA Method TO-17, EN ISO16017-1, ASTM D 6196

Typical TD-GC analytical conditions:Sampling: Pumped sampling: 2-20 L

Sorbent: Typically multi-sorbent


Desorption: 5 mins at 280ºC (depends on sorbent)

Trap: Tenax TA or dual bed -10 to 300ºC

Split: During trap desorption only ~15:1


Reference: TDTS28 on monitoring indoor air

Thermal Desorption: A Practical ApplicationsGuide. II. Residual Volatiles & MaterialsEmissions Testing

Clean indoor air pumped onto multi-sorbent tube andanalysed by TD-GC-MS


1,1

-diflu

oro

ethan

e

Eth

anol

Isopen

tane

1,1

-diflu

oro

-1-c

hlo

roet

han

eD

ichlo

rodiflu

oro

met

han

e

1,1

,1,2

-tet

rafluoro

ethan

e

Hex

ane

Ace

tone

Freo

n 1

13

Propan

ol

Tric

hlo

rofluoro

met

han

e

Dic

hlo

rom

ethan

e

Met

hyl

cycl

ohex

ane

Ben

zene

Tetr

achlo

rom

ethan

e

Eth

yl a

ceta

te

Hex

anal

Tolu

ene

Eth

yl b

enze

ne

Eth

ylcy

clohex

ane

o/p

xyl

ene

Tetr

achlo

roet

han

e

α-p

inen

e

Trim

ethyl

ben

zene

Dec

ane

Sty

rene

Lim

onen

e Undec

ane

Ben

zyl al

cohol

Nonan

alD

odec

ane

Trid

ecan

e

Tetr

adec

ane

Monitoring car cabin air Background:Car cabins are small confined spaces. Vapour-phase (S)VOC levels can build up – especially inparked cars on a hot day. Car manufacturers andtheir suppliers are currently focused on improvingthe quality of cabin air and reducing emissionsfrom vehicle trim components. This will reducethe exposure of drivers and passengers. Pumpedsampling onto sorbent tubes with TD-GC-MSanalysis is the method of choice for profiling carcabin air.

Std. methods: EN ISO 16017-1, ISO 16000-6,ASTM D6196

TD-GC analytical conditions:Sampling: Pumped sampling of 2 L volume

Sorbent: Tenax TA or multi-sorbent



Trap: Tenax or dual bed -10 to 300ºC

Split: 75:1


Reference: TDTS33 on profiling car cabin air

Air from the cabin of a small saloon car showing acomplex range of VOCs and high total-VOC levels

Saloon car cabin air 23°CTVOC 3.7 ppm

Saloon car cabin air 40°CTVOC 9.7 ppm

MEKn-H

exan

eBen

zene

Cyc

lohex

ane

Eth

yl b

enze

ne

n-O

ctan

e

Isooct

ane

NN

DM

FTo

luen

e

Met

hyl

cycl

ohex

ane

Hep

tane

Eth

yl t

olu

ene

n-N

onan

eo-X

ylen

eSty

rene

m-/

p-x

ylen

e

Trim

ethyl

ben

zene

n-D

ecan

eD

imet

hyl

ben

ylam

ine

C11

C11/1

2C

12

C13

Cubeb

ene

/ Copae

ne

n-C

13

Sily

l es

ter

2-(

2-b

uto

xy-e

thox

y)et

han

ol

o-x

ylen

eSty

rene

m-/

p-x

ylen

eEth

yl b

enze

ne

Tolu

ene

NN

DM

F

Met

hyl

cycl

ohex

ane

n-d

ecan

eTr

imet

hyl

ben

zene

n-n

onan

e

Dim

ethyl

ben

zyla

min

eC

11

C11/1

2C

12

C13

2-(

2-b

uto

xy-e

thox

y)et

han

ol

Copae

ne

n-C

13

Sily

l es

ter

Dodec

ane n-C

14

Typical analytes:• Benzene

• 1,3-butadiene

• General VOCs

Concentrations: Sub to low ppb

Personal exposure indoors Background:TD is used for several applications relating to ‘SickBuilding Syndrome’. Here, diffusive tube samplerswere used with subsequent TD-GC-MS analysis forindoor & outdoor air sampling & simultaneouspersonal monitoring. Diffusive (passive) samplers areunobtrusive, low cost (no pumps) & simple to deployfacilitating personal exposure assessment & largescale studies of indoor air quality & human exposure.

Std. methods: EN 14662-4, EN ISO 16017-2,ASTM D6196

Typical TD-GC analytical conditions:Sampling: Diffusive sampling

Sorbent: Carbograph 1TD, Carbopack X or Tenaxdepending on target analyte range



Trap: Dual carbon -10 to 320ºC

Split: ~10:1 during trap desorb only


Reference: TDTS10 on diffusive sampling inindoor air, TDTS01 on uptake rates, TDTS54on personal exposure to 1,3-butadiene.

Poor indoor air quality and high personal exposure inthis home were linked to a diesel car parked in a

garage under the living space


Outdoor

Personal

Indoor

Typical tracer gases:• PDCB – perfluorodimethylcyclobutane

• PMCP – perfluoromethylcyclopentane

• PMCH – perfluoromethylcyclohexane

Concentrations: ppt to low ppb

Building ventilation tests withtracer gases

Background:To test building ventilation, sources of individualperfluorocarbon tracer gases are placed indifferent rooms. They are sampled, diffusively orwith pumps, onto sorbent tubes. Use of diffusionreduces monitoring costs. After sample collectiontubes are analysed via TD-GC-MS/ECD. The riseand subsequent decay in tracer gas concentrationsallows the building ventilation (rate of air exchange)to be monitored.

Typical TD-GC analytical conditions:Sampling: Diffusive or pumped

Sorbent: Carbograph 1TD (40-60 mesh)



Trap: Carbograph 1TD -10 to 300ºC

Split: ~10:1

Analysis: GC-MS or ECD

Reference: H. Bloemen et al.,‘Ventilation rate andexchange of air indwellings’, RIVM,Netherlands, 1992

FirstFloor

GroundFloor

PMCH

PMCP

PDCB

PDCB

PMCP

PMCH

Typical analytes:• Solvents

• Hydrocarbons and haloforms

• Ketones, esters, glycol ethers

• Amines and nitriles

Concentrations: ppb to low ppm

Occupational hygiene -monitoring inhalation exposure

Background:Health and safety at work legislation requirespersonal exposure assessment of workerspotentially exposed to toxic chemicals. Pumped ordiffusive sampling onto sorbent tubes followed byTD-GC(-MS) analysis provides a solvent-free, safeanalytical option with ~1000 x more sensitivitythan conventional charcoal tube / CS2 extractionmethods. TD tubes are also reusable indefinitely.

Std. methods: UK MDHS series, EN ISO 16017,ASTM D 6196, NIOSH 2549

Typical TD-GC analytical conditions:Sampling: Diffusive or pumped

Typical sorbent: Tenax or Chromosorb™ 106


Desorption: 5 mins at 300ºC or 200ºC (for C106)

Trap: Tenax or Tenax/Carb 1TD from -10 to 300ºC

Split: 50:1 to 500:1

Analysis: GC-MS(SCAN) or ECD

Reference: TDTS37 on industrial airmonitoring, TDTS38 on occupationalexposure limit levels, TDTS50 on workplacemonitoring

Reactive amines inworkplace air

Personal exposure tosolvents at work

PNCB

FAN

1PP

D

4N

4A


Sulp

hur

dio

xide

Ben

zene

1-c

hlo

ro-1

,3-b

uta

die

ne

Car

bon d

isulp

hid

e

Ace

tone

Chlo

rofo

rm

Typical analytes:• Solvents

• Hydrocarbons and haloforms

• Ketones, esters, glycol ethers

• Amines and nitriles

Concentrations: ppb to low ppm

Diffusive (passive) sampling inthe workplace

Background:Unobtrusive, low-cost diffusive samplers facilitatepersonal exposure monitoring because they can beworn close to the breathing zone withoutimpacting worker behaviour. Analysis by thermaldesorption means tubes are re-usable indefinitely.The enhanced sensitivity of TD, relative to solventextraction, also allows compliance with new lowerthreshold limit values.

Std. methods: UK MDHS series, EN ISO 16017,ASTM D 6196, NIOSH 2549

Typical TD-GC analytical conditions:Sorbent: Tenax, carbon or porous polymer


Desorption: 5-10 mins. Temp depends on sorbent

Trap: Dual sorbent -10 to 300ºC

Split: Between 50:1 and 500:1

Analysis: GC(-MS)

Reference: TDTS01 on uptake rates, TDTS08on principles of diffusive sampling, TDTS38on limit levels, TDTS50 on workplacemonitoring

Standard sorbent tube fitted with adiffusion cap at the sampling

(grooved) end

Analytes:Dichlorvos DiazinonChlorpyrifos MethacrifosEtrimfos PhosfamidonChlorpyrifos-methyl Pyrimifos-methylFenitrothion Malathion

Concentrations: ppb

Monitoring inhalation exposureto pesticides

Background:Agricultural workers involved in pesticideapplication must be monitored to ensure that theirexposure to these highly toxic chemicals does notexceed safe levels. Pumped monitoring using inert(glass or Silcosteel) tubes together with TD-GC-MSanalysis provides a reliable and highly sensitivemonitoring method.

Std. methods: UK MDHS series, EN ISO 16017-1,ASTM D 6196, NIOSH 2549

Typical TD-GC analytical conditions:Sampling: Pumped

Sorbent: Tenax in glass or Silcosteel tubes



Trap: Tenax -10 to 300ºC

Split: ~10:1 during trap desorption only

Analysis: GC-MS

Reference: TDTS39 on using TD withSecureTD-Q to monitor vapour phasepesticides

Primary and repeat analysis of pesticides for personalexposure monitoring


Dic

hlo

rvos

Met

hac

rifo

s

Chlo

rpyr

ifos

Mal

athio

nM

ethyl

pirim

ifos

Fenitro

thio

n

Met

hyl

chlo

rpyr

ifos

Phosp

ham

idonE

trim

fos

Dia

zinon

Typical analytes include:• Halogenated solvents

• Styrene

• Ketones

• Aromatics

Biological monitoring viaalveolar breath

Background:Biological exposure monitoring allows assessmentof the whole body burden of chemicals via allroutes of exposure – skin absorption, ingestionand inhalation. Alveolar breath sampling using thedisposable Bio-VOC allows large-scale, non-invasivebiological monitoring of workers using PPE orhandling skin-absorbed chemicals. After breathcollection, the sample is discharged into a Tenaxtube and analysed by TD-GC-MS.

Official guidance: Suite of breath samplingguidance notes available from UK HSL.

Typical TD-GC analytical conditions:Sorbent: Tenax TA (35-60 mesh)



Trap: Tenax TA -10 to 280ºC

Split: ~10:1


Reference: TDTS13 Evaluation of theBio-VOC, TDTS48 Overview of breathsampling

Skin-absorbed solvents in the breath of shoe workerscollected using the Bio-VOC™

Ace

tone

2-b

uta

none

1-m

ethyo

xy-2

-pro

pan

ol

Tolu

ene

Xyl

ene

The Markes International advantage

• Markes leads the market in TD

• Unparalleled reputation for product quality andreliability

• Excellence in technical and applications support

• For further information on Markescomprehensive range of instruments, samplingaccessories and consumables please use one ofthe contact numbers / email address below orbrowse the web site

Trademarks

UNITY™, ULTRA™, Air Server™, µ-CTE™, SafeLok™, DiffLok™, VOC-Mole™,Bio-VOC™, TT24-7™, TC-20™, UniCarb™ and SecureTD-Q™ are trademarks ofMarkes International Ltd., UK

Tenax TA™ is a trademark of Buchem B.V., Netherlands

Carbograph 1TD™ is a trademark of LARA s.r.l., Italy

Carbopack X™ is a trademark of Supelco Inc., USA

Silcosteel™ is a trademark of Restek Inc., USA

Chromosorb 106™ is a trademark of Manville Corp., USA

The Markes International team


Markes International Ltd.

Gwaun Elai Medi Science CampusLlantrisant

RCTCF72 8XL

United Kingdom

T: +44 (0)1443 230935 F: +44 (0)1443 231531E: [email protected] W: www.markes.com

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w.m

ark

es.co

m

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