thermal desorption: a practical applications guideintroduction to markes international ltd. formed...

Thermal Desorption:A Practical Applications Guide

IV. Food, Flavour, Fragrance &Odour Profiling www.m

arkes.com

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, the AirServer™ interface for canisters and on-line sampling,the µ-CTE™ Micro-Chamber / Thermal Extractor formaterials testing, the TT24-7™ for continuous on-line monitoring and the TC-20™ multi-tubeconditioner.

Markes International also supplies a wide range ofsampling accessories and consumables for all TDapplication areas.

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

OverviewThermal 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 (SVOC) in productsand materials. Examples include residual solvents inpackaging & pharmaceuticals, materials emissionstesting and food / flavour / fragrance profiling.

This publication presents several of the real worldapplications of TD for measuring (semi) volatiles infood, flavour, fragrance and odours. Accompanyingpublications cover the applications areas of:

• Residual volatiles and materials emissionstesting

• Defence & forensic• Environmental monitoring and occupational

health & safety

Applications• Fragrance profiling of ingredients in toiletries

and consumer products• Identification of key olfactory components• Characterisation / sourcing of natural

products• Odour profiling for potable spirits• Quantitation of volatile components in dried

foodstuffs• Off-odour / taint analysis• Biology / crop research• Flavour profiling of GM foods

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

Background:Detailed analysis of natural oils (e.g. sesame oil)may be required for several reasons; to identifykey olfactory components, to characterise andsource the material, and to identify oxidationproducts or other potential causes of taint.Traditionally this application has been carried outusing multi-step liquid extraction or steamdistillation with GC-MS analysis, but suchprocedures are lengthy, manual and inefficient.Direct thermal desorption/extraction of the oilusing either the TD tube itself or a MarkesMicro-Chamber / Thermal Extractor (µ-CTE)device, followed by TD-GC-MS analysis is a moreefficient alternative.TD conditions:Sampling: Either incubate the oil sample in aµ-CTE chamber at 80 - 100ºC with vapourcollection on Tenax TA™ tubes (gas flow~100 ml/min) or load a few mg of oil onto aglass wool plug behind a 1 cm bed of Tenax in astandard TD tube. Desorption: 10 mins at 300ºCCold trap: TenaxSplit ratio: >100:1Analysis: GC-MS (SCAN)

Profiling natural oils

Direct desorption of sesame oil sample, followed by asecond desorption of the tube to illustrate efficient

recovery of the components of interest in a single run

7.5 mg Sesame Oil

Redesorption of same tubeEmpty tube showing system background

Typical analytes:Methyl pyrazines, fatty acids and ethyl vanillin

Concentration: Low to high ppm

Meth

yl py

razin

e2-

Fura

nmeth

aneth

iolTri

meth

yl py

razin

eAc

etyl p

yraz

ine Oleic

Acid

Tetra

cosa

hexa

ene

Direct desorption of volatilesfrom dried foodstuffs Background:

Direct desorption of homogeneous dried foodsprovides a high sensitivity and labour savingalternative to solvent extraction and allowsanalysis of a wider volatility range of componentsthan equilibrium headspace. Foodstuffs compatiblewith this approach include:• Ground spices • Freeze-dried products such as ground or

instant coffee • Animal feed pellets

Typical TD-GC analytical conditions:Sampling: 100–200 mg weighed into empty glasstube or PTFE linerTD system: ULTRA-UNITYDesorption: 10 mins at 80°CTrap: Quartz wool / TenaxSplit: ~25:1 split during trap desorption onlyAnalysis: GC-MS (SCAN)

Reference: TDTS23 Utilising the UNITYmethod development mode to analyse driedfoodstuffs

Direct desorption of dried animal-feed pellets weighed into an empty glass tube

Typical analytes:Carvacrol, cineole, thymol, eugenol and hydrocarbonsConcentration: Sub to low ppm


n-C 1

0

Euca

lypto

lNo

nana

lDo

deca

neTh

ymol

Euge

nol

Tetra

deca

neHe

xade

cane

Natural products:Fragrance profiling Background:

Markes TD systems have an inert flow path thatcan be set at low temperatures, which makesthem ideal for the direct desorption of labilevolatiles such as terpenes and sulphur compounds.SecureTD-Q™ (i.e. quantitative re-collection of allsplit flow) facilitates repeat analysis of a sampleunder the same or different conditions (e.g. at alower split setting, as shown) to demonstratequantitative recovery through the system and toallow detailed analysis of minor components. Typical TD-GC analytical conditions:Sampling: ~100 mg of leaf sample weighed intoan empty glass tube or PTFE liner secured withquartz woolRe-collection on Tenax / UniCarb™ Silcosteel™tubesTD system: ULTRA-UNITYDesorption: 10 mins at 80°CTrap: Sulphur trapFlow path: 80°C to 150°C depending on targetcompoundsSplit: ~25:1 & repeat analysis at 5:1 split.Analysis: GC-MS (SCAN)Reference: Markes brochure on TD validationfeaturing SecureTD-Q

Vapours extracted from a leaf sample. Directdesorption (blue trace) followed by repeat analysis ofre-collected sample (black trace) run with lower split

ratio to enhance sensitivity

Typical analytes:Range of terpenoid compounds, including:α-Cedrene, α-Cadinene and T-Cadinol

Concentration: Sub to low ppm

α-Co

paen

e

α-Be

rgam

oten

e

Germ

acre

ne-D

α-Ca

dinen

e

DEP T-

Cadin

ol

Background:Development of new food crop species (e.g.genetic modification to aid pest resistance or toboost growth in arid areas) requires tests of theodour profile to make sure that the flavour isenhanced, or at least remains acceptable, in thenew variety.In the case of bulk, inhomogeneous materials likefresh fruit / vegetables, flavour profiles are bestobtained by purging headspace volatiles fromlarge (~ 1 kg) samples, cooked or raw, andcollecting the vapours on tubes packed with Tenaxsorbent. Tenax is completely hydrophobic so mostwater passes straight through during the vapoursampling process.

Typical TD-GC analytical conditions:Sampling: 50 ml/min for 20 mins Prepurge: 3 mins (to trap & split)Desorption: 15 mins at 200°CTrap: Tenax TASplit flow: 20 ml/minAnalysis: GC-MS

Flavour profiling new cropvarieties

TD-GC-MS analysis of volatiles from boiling potatoesusing SecureTD-Q: Original sample and re-collectedsample. Identical chromatographic profiles show

recovery of labile analytes (e.g. terpenoids)Analytes:Diethyl phthalate, n-butyl butyrate, α-copaene, 2-(2-butoxyethoxy)-ethanol, 2-phenoxyethanol, decanal,octanoic acid, 2-ethylhexanoic acid, nonanal, 2-pentylfuran, pentanol, and hexanal

Concentration: Sub to low ppm


Pent

anol

2-Pe

ntylf

uran

2-Ph

enox

yeth

anol

α-Co

paen

e

DEP

Re-collectedsample

Original

Fragrance profiling inconsumer products Background:

Fragrance plays a major part in market acceptanceand consumer satisfaction for products such assoaps & other toiletries, air fresheners anddomestic cleaning materials.TD provides a versatile, labour-saving andautomated tool for GC-MS analysis of thefragrance profile of consumer products offeringnumerous sample handling options:• Direct, in-tube desorption • Dynamic purging of headspace vapours with

on-line analysis• Dynamic purging of headspace vapours onto

sorbent tubes with off-line analysisTD allows selective elimination of potentialinterferences such as water and some solventsthus simplifying fragrance analysis.Typical TD-GC analytical conditions:Sampling: ~200 ml headpace sampled onto TenaxtubesTrap: U-T2GPHSplit flow: 30 ml/min during tubeand trap desorptionAnalysis: GC-MS

Headspace from sample of fabric conditioner

Analytes:Isopropyl alcohol α-Pinene β-Pinene α-Longipinene Hexene-1-ol CamphorMethyl-β-ionone γ-Terpinene MyrceneD-limonene Triplal 1 LinaloolHydroxy citronellal α-Cedrene γ-MuuroleneThujopsene β-Ionone α-ChamigreneCyclamen aldehyde α-Cedrol α-Longipinene

Concentrations: ppm in headspace

Hexe

ne-1

-ol

α-pin

ene

D-Lim

onen

eTri

plal

Linalo

ol

α-ce

dren

eTh

ujops

ene

Meth

yl-β-

ionon

e

Breath from 6 non-smokers

Breath from 2smokers

Halitosis – bad breath Background:We are what we eat – and sometimes it comesback to haunt us in the shape of bad breath!Halitosis can also be caused by bacterial infectionsof the mouth / throat, some disease states andsmoking.The Bio-VOC™ Breath sampler from MarkesInternational collects breath samples from themouth & bronchial passages or from the alveoli(end-tidal air) and transfers them to sorbent tubesfor subsequent analysis by TD-GC-MS. Applicationsof the Bio-VOC include biological monitoring ofenvironmental / workplace exposure and diseasediagnosis as well as breath odours.

Typical analytical conditions:Sampling: Breath exhaled into Bio-VOC samplerand transferred to Tenax tube or Tenax /Carbograph 1TD focusing trapDesorption: 280ºC for 10 minsTrap: U-T2GPHTrap conditions: +30ºC to320ºC for 3 minsAnalysis: TD-GC-MS or TDwith process-MS

Rapid TD-MS analysis of benzene and otherhydrocarbons in the breath of smokers & non smokers

Typical analytes:Hydrocarbons, oxygenates (esters, ketonesalcohols, etc.) and other odorous VOCsConcentrations: Low ppb


= benzene= toluene= isoprene

Taint and off-odour Background:Product taint can be introduced via: • Odorous base materials• Issues with the fragrance itself• Packaging – everything from printed film to

wood pallets• Warehousing

Gentle direct desorption of the tainted product, viaTD tubes, micro-chambers or bulk sample vesselsand comparison with equivalent data from a controlsample allows the taint components to be identified.The source can then be tracked via direct desorptionof packaging, pallet fragments, base materials,additives etc. and analysis of vapour profiles andwarehouse air collected on sorbent tubes.Typical analytical conditions for PET:Sampling: 200 mg of ground polymer in an emptytubeDesorption: 160ºC for 10 minsTrap: U-T6SULTrap conditions: -10ºC to 300ºCSplit: 40 ml/min during trapdesorptionAnalysis: GC-MS

Direct desorption of ground polyethyleneterephthalate (PET) polymer to identify trace level

VOCs contributing to taint. Comparison of PETpolymers used in manfacture of soft drinks bottles

Typical analytes:Residual monomers (e.g. acetaldehyde), pyrazolesand solventsConcentrations: Sub to low ppm

Sample AAceta

ldehy

de

Sample B

Sample C

Sample D

1,3-

Diox

olane

Ethy

lene g

lycol

Direct desorption of packaging Background:VOCs in food packaging can cause taint. In thisexample, TD was used to analyse printed biscuitwrappers in two ways:• Direct desorption of the wrapper• Desorption of Tenax TA tubes used to collect HS

vapours from the sampleNote that headspace vapours from the packagingsample show high levels of volatile solvents whichcan migrate into fatty food stuffs, adverselyaffecting the taste.Typical TD-GC conditions:Sample: 10 x 5 cm area of film, rolled & insertedinto an empty glass tube for direct desorption &250 ml headspace sample drawn into a Tenaxsorbent tube TD system: ULTRA-UNITYDesorption: 10 mins at 60°C (direct TD) and 10mins at 300°C (HS sample on Tenax tube)Trap: Quartz wool, Tenax TA, Carbopack X™Split: 30:1 during trap desorptionAnalysis: GC-MS

Typical analytes:Alcohols, esters, ketones, alkanes and other odoroussolvents

Direct desorption of residual solvents and semi-volatileadditives from printed packaging film and sorbent tube

sampling of headspace vapours from same


1- Pr

opan

ol Ethy

l ace

tate

Pentamethyl heptane

Pent

anoic

acid

2,2,

4-tri

meth

yl-3-

carb

oxyis

opro

pyl,

isobu

tyl es

ter

Ethy

l ace

tate

Directdesorption

Headspacevapours

Trichloroanisoles in wine Background:A recent high-profile example of taint was linkedto 2,4,6-trichloroanisole (TCA) in wine. TCA isproduced from trichlorophenol by a microorganismthat thrives in the production process of corks forwine bottles. This and other chemically similaranalytes give the wine a mushroomy ‘corked’aroma even at low concentrations (<5 ng/L). The inert flow path of Markes TD systemsfacilitates TCA measurement in the headspace ofaqueous samples at sub ng/L levels. The Markes µ-CTE also facilitates direct thermalextraction of whole corks.

Typical TD-GC analytical conditions:Sampling: On- or off-line sampling of headspacefrom 1 L aqueous samples at 60ºC onto Tenaxtrap. Whole cork incubated at 60ºC using µ-CTEwith 70 ml/min flow of helium for 10 minsDesorption: 280ºC for 10 minsTrap: U-T2GPHTrap conditions: -5ºC to 300ºC Split flow: 30 ml/minAnalysis: GC-MS or GC-olfactometry

TD analysis of 0.2 ng/L TCA and other odourcompounds in the headspace of 1 L aqueous sample.

Inset: Vapour profile from whole cork using m-CTE

Analytes:• 2,4,6-Trichloroanisole• 2,3,4,6-Tetrachloroanisole• 2,4,6-TribromoanisoleConcentrations: Sub tolow-ppb

2,4,

6-Tri

chlor

oanis

ole

Geos

min

2,3,

4-Tri

chlor

oanis

ole

Tribr

omoa

nisole

Thermal extractionof cork using µ-CTE

Odours from meat-processing Background:Thermal desorption is used extensively to monitorodours associated with meat processing.Applications include environmental / ambient-odour monitoring, product quality / flavourassessment, testing of animal odours (healthy anddiseased) and at-line monitoring of productionprocesses.

Typical TD-GC analytical conditions:Sampling: 0.5-2 L vapour sampled onto Tenax /Carbograph 1TD tubesDesorption: 300ºC for 5 mins then 320ºC for5 minsTrap: U-T2GPHTrap conditions: +20ºC to 300ºCSplit: Low split during trapdesorption onlyAnalysis: GC-MS

Chromatogram reproducedwith the kind permission ofAPS Adamsen, of LugTek,Denmark - experts in odoursfrom livestock production

Chromatogram of odours from a swine facility

Typical analytes:Carboxylic acids, monoterpenes, phenolic compounds,amines and amidesConcentrations: ppb

α-Pine

ne

3-Hy

drox

y-2-

buta

none

Aceti

c acid

2-Me

thyl

prop

anoic

acid

Buta

noic

acid

Pena

tano

ic ac

id

Hexa

noic

acid

4-Me

thyl

phen

ol

Hexa

deca

noic

acid


1,5-

Pent

aned

iamine

1-He

xana

mine

Buta

nami

de

Multi-purpose Direct InletAccessory – For direct sampling /concentration of headspace vapours

The multi-purpose DirectInlet Accessory (U-INLET)may be added to any manualUNITY thermal desorptionplatform to provide a simpleand convenient mechanismfor concentration ofheadspace vapours from awide range of bulk samplecontainers.

This on-line approach allows vapours to be eitherpumped or swept through an inert, heated samplingline directly into the electrically-cooled focusing trapof UNITY without first being collected on a sorbenttube.

The UNITY-Direct Inlet system significantly improvesthe sensitivity of conventional headspace methods byallowing multi-stage extraction and concentrationbefore analysis. The dynamic headspace approachalso eliminates the need for equilibrium to bereached, thus reducing the time required for analysis.

Sample vessel

The UNITY-Direct Inlet system is compatible with awide range of sample vessels. It may be used forpurging headspace vapours from smaller, sealedcontainers (such as reaction vessels or headspacevials) or for pumping air from open or compressiblecontainers such as bell jars or Tedlar™ bags.

Key application areas include:

• Characterisation of VOC profiles from naturalproducts and manufactured goods - food,flavour, fragrance analysis

• Monitoring emissions from living organisms -plants, microbes, fungi, insects, etc. as theychange with time

• Monitoring malodours generated from foodpackaging (e.g. drink bottles)

• Off-odour / shelf-life testing• Sampling from drinks / spirits, with the

option of selectively purging the ethanol

UNITYtrap

Optional pump

Gas/air inlet

Whisky: Aroma profiling Background:Thermal desorption facilitates detailed analysis ofthe flavour profile of potable spirit by allowingselective elimination of water and ethanol whilekey olfactory components – ketones, esters,essential oils, etc. – are quantitatively retained. Headspace vapours are pumped / purged ontoTenax tubes under conditions which concentratethe target analytes while allowing most of thewater, ethanol and other very volatile polarcomponents to breakthrough. An example ofwhisky analysis, with and without selectiveelimination of water and ethanol, is shownopposite. Selective concentration of key olfactorycomponents simplifies meaningful odour profiling.

Typical TD-GC analytical conditions:Sampling: Sample placed in headspace vial at~40°C. Connected to UNITY via Direct HeatedInlet AccessorySampling mode: Pulsed mode,6 extractions of headspaceTrap: Tenax TAAnalysis: GC(-MS)

Purging of water and ethanol from whisky HSvapours allows selective concentration of key olfactory compounds – ketones, esters, etc.

Typical Analytes:Ketones, aldehydes, estersessential oils (e.g. juniper and coriander in gin)

Concentrations: Sub to low ppmMarkes International Ltd.

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

WITH post-sampling purgeEthanol represents <30% of total peak area

NO p

ost-s

ampli

ng p

urge

Etha

nol r

epre

sent

s >99

% of

tota

l pea

k are

a

Resid

ual e

than

ol

Micro Chamber / Thermal Extractor(µ-CTE)The µ-CTE offers aconvenient approach forsampling volatiles frombulk samples at low tomoderate temperatures.

The µ-CTE contains six (6)28 mm deep x 45 mmdiameter chambers intowhich samples are placed.A controlled flow of air orcarrier gas is purged through all of the chamberssimultaneously, sweeping the volatiles onto sorbenttubes attached to each chamber lid.

The µ-CTE can be heated from ambient to 120°C andis available with stainless steel or Silcosteelchambers. It is convenient for samples which are tooinhomogeneous for direct desorption in empty tubes.µ-CTE accessories are available to facilitate surfaceemissions testing and permeation studies (e.g. ofpackaging) as well as volatile analysis in bulksamples.

Key Applications include:

• Bulk sampling of volatiles from fruits,vegetables and other inhomogeneousfoodstuffs

• Fragrance profiling of tobacco blends /substitutes

• Permeation testing of packaging• Fragrance profiles from consumer products

Fragrance profiling of toiletriesusing the µ-CTE Background:

The Markes µ-CTE is ideal for fragrance profiling ofaqueous solutions and emulsions such asshampoo. Six replicate or different shampoosamples can be measured into individual micro-chambers, incubated at low temperatures (e.g.30-40ºC) and the fragrance components purgedonto attached sorbent tubes. Use of hydrophobicsorbents in the tubes allows quantitative retentionof organic compounds of interest while water ispurged to vent.The µ-CTE is compatible with air or inert carriergas to allow analysis of product fragrance underinert or oxygenating conditions.

Typical TD-GC analytical conditions:Sampling: 5 ml shampoo incubated in the µ-CTEat 30ºC. Vapours swept onto Tenax tubes in a70 ml/min flow of helium for 5 minsDesorption: 280ºC for 10 minsTrap: U-T2GPHTrap conditions: 30ºC to 300ºC for 3 minsSplit flow: 30 ml/min during trap desorptionAnalysis: GC-MS

Typical Analytes:Esters, fatty acids, terpenes and solvents

Concentrations: ppm

Fragrance profile from shampoo obtained using theµ-CTE


Ethy

l ace

tate

Cyclo

hexa

ne Buta

noic

acid

3-Me

thylb

utan

olac

etate

D-Lim

onen

eHe

xena

l ace

tate

aceti

c acid

, phe

nylm

ethyl

ester

2-(1

,1-d

imeth

yleth

yl)-

cyclo

hexa

nol

2-ph

enox

yeth

yliso

butyr

ate

Flavour profiling of dairyproducts Background:

Milk and related dairy products have a complexaroma profile comprising fatty acids, lactones,ketones, aldehydes, esters, and hydrocarbons.Several millilitres of milk or yoghurt can beconveniently measured into stainless orSilcosteeled micro-chambers and incubated attemperatures between ambient and 80ºC under aflow of pure air or inert carrier gas. Emittedvapours are collected on Tenax tubes connected tothe exhaust of each micro-chamber. Water isselectively eliminated.

Typical TD-GC analytical conditions:Sampling: 10 ml (g) yoghurt incubated at 70ºC inthe µ-CTE, swept onto Tenax tubes in a 70 ml/minflow of helium for 10 minsDesorption: 280ºC for 10 minsTrap: U-T2GPHTrap conditions: 30ºC to 300ºC for 3 minsSplit flow: 30 ml/min during trapdesorptionAnalysis: GC-MS

Flavour profile obtained from natural greek yoghurt

Typical analytes:Lactones from octalactone to tetradecalactone, fatty acids from C6 to C16, C5 to C15 ketones, C6 to C14 aldehydes, esters from ethyl butanoate toethyl decanoate and C12 to C20 hydrocarbons

Concentrations: Sub to low-ppm in headspace

Hept

anon

en-

C 9

Thiop

heno

ne

Hept

anal Octa

nal Et

hylhe

xano

lLim

onen

e2-

nona

none

Nona

nal

Deca

nal

Unde

cana

l

Flavour profiling of cheese Background:There is extensive research into the complexaroma profiles of different types of cheese. Forexample, over fifty aroma-active compounds havebeen detected in cheddar cheeses.Thermal desorption / dynamic headspace offers anautomated and versatile alternative to multi-stepliquid extraction and vacuum distillation. Smallcubes of cheese or grated cheese slurries mixedwith distilled water can be incubated (e.g. usingthe Markes µ-CTE) purged with inert gas or pureair and the vapours collected using on- or off-linesorbent traps. Subsequent analysis is by TD-GC-MS or TD-GC with olfactometry.

Typical TD-GC analytical conditions:Sampling: 2 g grated cheese mixed with 5 mlwarm water and incubated in the µ-CTE. Vapoursswept onto Tenax tubes in a 70 ml/min flow ofhelium for 10 minsDesorption: 280ºC for 10 minsTrap: U-T2GPHTrap conditions: 30ºC to 300ºC for 3 minsSplit flow: 30 ml/min during trap desorptionAnalysis: GC-MS

Aroma / flavour profiling of cheese using the µ-CTE

Typical analytes:Ketones, lactones, pyrazines, sulphurous compounds,esters, aldehydes, free fatty acids and alcohols Concentrations: Sub to low-ppm in headspace


n-C 8

Hexa

nal

Hept

anon

en-

C 9He

ptan

al

Hexa

noic

acid

Pent

ameth

yl he

ptan

eOc

tana

lLim

onen

e

Deca

nal

Nona

nal

Deca

nal

2-No

nano

ne

Applications for thermaldesorption in the tobacco industry Background:

In addition to sampling / analysis of environmentaltobacco smoke (ETS), thermal desorption hasextensive uses in the tobacco industry. Keyapplications include:• Aroma profiling of tobacco / tobacco substitutes• Monitoring filter efficiency by collecting vapours

from smoking machines (see opposite)• Tracking the cause of taint in batches of tobacco

productsThese applications are carried out using sorbenttube sampling, direct thermal desorption andsampling accessories such as the µ-CTE.Typical analytical conditions:Sampling: Multiple “puff” volumes taken into bag,then transferred onto sorbent tube or vapourssampled directly into tubeDesorption: 280ºC for 10 minsTrap: U-T2GPH, 30ºC to 300ºC for 3 minsSplit flow: 30 ml/min during trap desorptionAnalysis: GC-MSReference: TDTS76 Applications of thermaldesorption in the tobacco industry

VOC profile of tobacco smoke drawn through acigarette filter, using a smoking machine

Analytes:Benzene, toluene and isoprene

Concentrations: Sub- to low ppb levels in air.Higher levels in headspace vapours

Isopr

ene Be

nzen

e

Tolue

ne

Data reproduced with the kind permission ofBritish American Tobacco, UK

Monitoring the aroma / flavourprofile of tobacco using the µ-CTE

Vapour profiles from “rolling” tobacco (top) andcigarette tobacco (bottom) collected using a stainless

steel micro-chamber at 50ºC

Typical analytes:Glycols, triacetin, acetic acid, pyridines, hydrocarbons

Concentrations: Various

Background:The Markes µ-CTE provides an ideal samplingaccessory for inhomogeneous materials such astobacco. Crumbled tobacco samples can be placedin Silcosteel micro-chambers, incubated attemperatures up to 120ºC and purged with air orinert carrier gas to sweep volatiles onto inertsorbent tubes. Subsequent analysis is via TD-GC-MS. The chromatograms opposite showcomparative odour profiles from two types oftobacco.The µ-CTE is similarly convenient for samplingwhole cigarette filters (before or after smoking),cigarette paper and cigarette packaging materials.

Typical analytical conditions:Sampling: 1 g of tobacco incubated in the µ-CTEat 50ºC. Vapours swept onto Silcosteel Tenaxtubes in a 100 ml/min flow of helium for 10 minsDesorption: 300ºC for 10 minutesTrap: U-T2GPHTrap conditions: -10ºC to 300ºCSplit: Double split, 300:1Analysis: GC-MS (SCAN)


Triac

etin

Aceti

c acid

3-(1

-Meth

yl-2-

pyrro

lidiny

l)-py

ridine

Prop

ylene

glyc

ol

2,6,

6-tri

meth

yl-bic

ycloh

epta

ne

Butyr

olacto

ne

VOCs from “rolling” tobacco

VOCs from cigarette tobacco

On- and off-line monitoring ofproduct shelf life Background:

Versatile TD sampling accessories like the MarkesMicro-Chamber / Thermal Extractor allow up to 6product samples to be simultaneously incubated ina stream of air or inert gas for accelerated shelf-life tests and odour studies. Vapours are collectedon attached sorbent tubes and analysed off-lineusing ULTRA-UNITY.Custom made sample containers for bulk fresh orprepared foods – pizza, canned meat, etc. – canalso be linked to off-line sorbent tubes ormonitored continuously using either the TT24-7or UNITY-Air Server / Direct Inlet. These on-lineTD systems allow near real-time assessment ofodour profiles as they change with time.

Typical on-line monitoring parameters:TD system: TT24-7, UNITY-Direct Inlet or UNITY-Air ServerSampling: 10-50 ml/min for 20 minsTrap: Tenax or U-T2GPH at +30ºCTrap desorption: 320ºC for 5 minsAnalysis: GC-MS or GC-olfactometry

Typical Analytes:Aldehydes, ketones, esters, sulphur and nitrogencontaining compounds, fatty acids, etc.

Concentrations: ppb to ppm

Markes’ continuous or semi-continuous TD systemsfor on-line monitoring of changing odour profiles

Twin trap TT24-7for continuousmonitoring

Air Server forsemi-continuous

monitoring

On-line monitoring offragrance profiles as they change

with timeBackground:Most natural (e.g. floral) fragrances and many ofthe fragrance profiles of consumer products, suchas air fresheners, change with time and ambientconditions. Markes continuous and semi-continuous on-line monitoring vapour systemsallow round-the-clock profiling of fragranceallowing changes to be tracked as a function oftime and ambient conditions – temperature,humidity, sunlight intensity, etc.

Typical on-line monitoring parameters:TD system: TT24-7, UNITY-Air Server, UNITY-Direct InletSampling: 10-50 ml/min for 20 minsTrap: U-T2GPHTrap conditions: -10ºC to 320ºC for 3 minsAnalysis: GC-MS


Concentrations of vapour phase organic compoundschanging with time

Time (HH:MM)

03:12 05:59 08:05

Typical Analytes:Aldehydes, ketones, esters, sulphur and nitrogencontaining compounds, fatty acids, etc.

Concentrations: ppb to ppm

SPE-tD™ cartridgesMarkes’ SPE-tD cartridges offer a simple, convenientmethod for sampling less volatile impurities inaqueous samples – applications which wouldotherwise require manually-intensive extraction ordistillation techniques before GC(-MS) analysis.

SPE-tD cartridges comprise a hollow tube, coatedinside and out with polydimethyl siloxane (PDMS) foroptimum capacity. The cartridge is placed into theaqueous sample and agitated. Volatile and semi-volatile organics in the sample, partition between theaqueous matrix and PDMS, reaching an equilibriumstate over time. This allows semi-quantitativeanalysis of less volatile organics and directcomparison of organic impurity levels in two similarsamples.

After equilibration, the SPE-tD cartridge is removedfrom the sample, rinsed in pure water to removesolid residues (if necessary) and placed into an emptyTD tube. The cartridge is then dry purged with purecarrier gas, on- or off-line, prior to analysis by directTD-GC-MS.Solid phase extraction / TD methods provide acomplementary sample preparation tool to automatedheadspace (HS) and purge-and-trap (P&T)techniques, which favour volatiles. Use of SPE-tDcartridges in combination with HS or P&T allows fullcharacterisation of aqueous samples.

Key Applications include:

• Off-odours / taints in drinking water• Semi-volatiles in processed fruit juices• Profiling of hydrosols (aqueous fraction from

steam distillation of natural oils)

SPE-tD extraction of organicsfrom drinking water Background:

High capacity solid phase extraction using MarkesSPE-tD cartridges provides a convenient approachto monitoring semi-volatile off-odour componentsin drinking water. SPE-tD cartridges used incombination with subsequent high sensitivity TD-GC-MS analysis offer trace detection limits (sub-ppb) and complement purge-and-trap /equilibrium headspace methods for volatiles.The example opposite shows sub-ppb impuritiesabsorbed by a SPE-tD cartridge from a 1 L sampleof drinking water.

Typical TD-GC analytical conditions:Sampling: SPE-tD cartridge placed into 1 L watersample and agitated for 2 hours Desorption: 60ºC for 10 minsTrap: U-T2GPHTrap Conditions: 30ºC to300ºC Split flow: 10 ml/min duringtrap desorption Analysis: GC-MS

Profile of sub-ppb level organics extracted fromdrinking water using the SPE-tD cartridge

Typical analytes:Geosmin, methyl isoborneol, phenols andtrichloroanisoles

Concentrations: Sub to low ppb


Dode

cane

Mono

chlor

oanis

oles

2-Iso

butyl

-3-m

ethox

ypyr

azine

2,4,

6-Tri

chlor

oanis

oleGe

osmi

n2,

3,4-

Trich

loroa

nisole

2,4,

6-Tri

brom

oanis

oledi

t-But

yl ph

enol

Drinking water: Pre-emptingodour complaints Background:

Much drinking water is sourced from natural riversand streams. Continuous on-line monitoring of theheadspace of river water, for unusually high levelsof key odour components such as geosmin, can beused to prevent tainted water entering thedrinking water supply and causing public concern. Analytical options include either UNITY-Air Serveror the TT24-7 on-line TD systems operatingcontinuously with GC-MS in unattended monitoringstations at strategically important points along theriver system. Hourly data from multiple remotefield monitoring stations can be sent to a centralnetwork hub by telemetry.

TD conditions:Trap: Tenax TA / Carbograph 1TDHeated inlet temp: ~70°CSampling flow rate / time: 50 ml/min; 15-20 minsPost sampling purge time: 15 mins at 50 ml/minTrapping temperature: 40°CDesorption: 300°C for 5 minsFlow path temperature: 200°CAnalysis: GC-MS

On-line monitoring of key odour components in the headspace of river water

Typical analytes:Methyl i-borneol, chloroanisoles and geosmin

Concentration: 200 ppt in example shown

Phen

ol 3-Ch

oroa

nisole

4-Ch

oroa

nisole

2-Ch

oroa

nisole

Trich

oroa

nisole

Geos

min

Tribr

omoa

nisole

The Markes International advantage

• Markes is the market leader in TD• Unparalleled reputation for product quality

and reliability• Excellence in technical and applications

support• For further information on Markes

comprehensive range of instruments, samplingaccessories and consumables please use one ofthe contact numbers / email address below orbrowse the web site

TrademarksUNITY™, ULTRA™, Air Server™, µ-CTE™, Bio-VOC™, TT24-7™, TC-20™,SecureTD-Q™ and SPE-tD™ are trademarks of Markes International Ltd., UKTenax TA™ is a trademark of Buchem B.V., NetherlandsCarbograph 1TD™ is a trademark of LARA s.r.l., ItalyCarbopack X™ is a trademark of Supelco Inc., USASilcosteel™ is a trademark of Restek Inc., USATedlar™ is a trademark of DuPont, USA

The Markes International team


www.markes.com

Markes International Ltd.Gwaun Elai Medi Science Campus

LlantrisantRCT

CF72 8XLUnited Kingdom

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

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