Basis of NonPolar Interactions_GC Columns PI

8/7/2019 Basis of NonPolar Interactions_GC Columns PI

1/9

GC SolutionsSeparation Science GC Solutions is the premier online resource or GC and GC/MS users working across the Asia Pacifc region.

Covering GC method undamentals, practicalities and troubleshooting it offers chromatographers and analytical chemists a genuine

e-learning platorm and searchable archive resource.

www.sepscience.com Issue 8: October 2010

Tech TipBasis o Interactions in Gas Chromatography,

Part 1 Non-Polar Interactions

To ully grasp the concepts o retention and selectivity o GC stationary phases,

one must frst understand the undamental intermolecular interactions that lead

to retention. This month we discuss the most dominant o those interactions

dispersive, non-polar interactions.

Click here to read more...

Featured Applications

Analysis o Butylated Hydroxytoluene in Foodwith Headspace Trap-GC/MS

Detecting Drugs o Abuse: EnhancedIdentifcation Using Benchto-dx andAssociated Sotware

Click titles to learn more

ProductsGC Pressure and Flow Calculations

iPhone/iPod Application

Separation o Drugs o AbuseClick titles to learn more


2/9

There are ewer types o intermolecular interactions available orinteractions between solutes and stationary phases in gas chromatographycompared to those possible in liquid chromatography.In addition, themobile phase in GC (the carrier gas) plays no role in adjusting or modiyingthe nature o intermolecular interactions during the run.So, the range opossibilities in retention orces and selectivity is much more limited in GCthan in LC.

In gas chromatography, molecules can only interact with each other

through intermolecular orces that all under the umbrella o van derWaals orces.They are listed in Table 1.Van der Waals orces can be overcome or disrupted by thermal motion,

which increases as temperature increases. This is why liquids evaporateaster when heated. and also why solutes are less retained (elute aster) ingas chromatography as the temperature is raised.

In gas chromatography, the dominant intermolecular attractive orce isdispersive interactions.Dispersive interactions are known also as temporarydipole interactions, because they result rom transient random distortionsin the electronic clouds o molecules, London forces, ater the scientist whofrst described them.Dispersive interactions exist between all molecules.

Basis o Interactions in Gas Chromatography,Part 1 Non-Polar InteractionsTo ully grasp the concepts o retention and selectivity o GC stationary phases, one must frst understand the

undamental intermolecular interactions that lead to retention.This month we discuss the most dominant o thoseinteractions dispersive, non-polar interactions.

Matthew Klee

Name Description Molecular traits Characteristic

Non-Polar

London2 (1930)

dispersion

induced dipole in-

duced dipole

All compounds,

non-polar interaction

Transient polarization,

scales with molecular size

Hydrogen bonding Extreme dipoledipole

interaction: H acceptor

interacts with H donor

Signifcant with

compounds containing

OH or -NH groups

Polar

Keesom3 (1912) dipoledipole Interaction between

strong dipoles

Electronegative groups

(e.g., halogens, -OR, -NOx,

-SOx)

Debye4 (1923) Dipoleinduced dipol e I ntera ct io n between

a strong dipole and a

weak dipole

More polarizable = easier

induction

Table 1

Table 1:Van der Waals1 forces of interactions between molecules.


3/9

Figure 1

Figure 1: London dispersive (non-polar) forces dominate the intermolecular interactions in gas

chromatography.They arise from spontaneous transient distortions, polarization, then coordinatedoscillations in electronic molecular orbitals. The larger the molecule, the larger the dispersive forces, thehigher the strength of interaction, and therefore the higher the retention.

-

---

--

+

+

+

+

+

+

-

-

-

-

--

+

+

+

+

+

+

Dispersive interactions are non-polar (also called apolar).Dispersiveinteractions arise rom random distortion o the electronic cloud o amolecule, causing a slight electrostatic polarization one side o themolecule becomes more negative, the opposite more positive (Figure 1).

This spontaneous polarization then induces an opposite polarizationin neighbouring molecules.The opposite charges attract and draw themolecules closer, urther distorting the clouds..A stabilizing oscillationo the charge distortion results within the bulk liquid (in wall coatedopen tubular columns, the stationary phase is considered a liquid). The strength o dispersive interactions track with the size o themolecule; the larger the molecule, the higher its mass, the moreelectrons, the higher the strength o its dispersive orces.Largermolecules have larger electron clouds which are more able to handleelectrostatic distortions.So, the distortions can be o higher magnitudeand o longer duration.For this reason, both boiling points and elutiontemperatures o molecules track with the size o the molecule (Figure 2).

Although retention in GC is based on the sum o all possibleinteractions, polar + non-polar, some types o molecules such assaturated hydrocarbons (alkanes) can only interact through dispersiveinteractions.Even i a stationary phase were to have polar unctionalgroups and thereore a signifcant possibility or polar interactions,saturated hydrocarbons would only interact with the non-polar,

dispersive aspect. The basic premise o retention in GC is illustrated in Figure 3.Onecan see in Figure 3 that the solute represented by the blue triangleshas a higher proportion o molecules in the stationary phase than inthe gas phase. As such, it migrates slowly through the column (has ahigh retention time).In contrast, the majority o the solute representedby the green squares is in the gas phase, so it will migrate much asterthrough the column (have a much lower retention time).

Retention in gas chromatography is an exponential unction otemperature.As temperature is raised, there will be a temperature atwhich the more retained solute (blue triangles) will travel at the same

The strength of dispersive interactionstrack with the size of the molecule; the largerthe molecule, the higher its mass, the moreelectrons, the higher the strength of its

dispersive forces.


4/9

Figure 3

Figure 3: Inner view o a capillary column. A flm thickness 0.5 m on a 250 m i.d. column represents a

phase ratio o 125, which is typical o capillary columns. As it is almost impossible to see the

stationary phase when drawn to scale, the inset shows a representation o the surace magnifed 100

times to better illustrated solute migration in/out o the phase.The solute with the weaker interactions

with the stationary phase (green squares) spends more time in the mobile phase and moves aster

through the column, eluting frst.The compound with stronger interaction with the stationar y phase

(blue triangles) spends less time in the gas phase and moves slower through the column.

250mi.d.

0.50mi.d.

magnified 100X

Column wall

stationary phase

carrier gas

column wall

Figure 2: (A) Retention time trend on-alkanes in a linear temperature programmed capillary GC run. (B)

Boiling point trend on-alkanes.Retention o in gas chromatography tracks boiling point because o

dominance o non-polar (dispersive) orces.

Figure 2

0

100

200

300

400

500

600

0 10 20 30 40 50

Carbon Numbern-Alkane

Boiling

Point(oC)

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50

Carbon number

RetentionT

ime

A

B


5/9

Figure 4

0

100

200

300

400

500

600

700

800

900

1000

0 25 50 75 100 125 150 175 200 225

Temperature (oC)

Reten

tionFactor(k)

Figure 5

1

10

100

1000

0 50 100 150 200 250 300

Temperature (oC)

RetentionFactor(k)

Solute A

Solute B

Solute C

solute D

speed as the less retained one in Figure 3 didat the lower temperature.As illustrated inFigure 4, retention decreases approximatelyby or each 23 oC change in temperature.In Figure 5, example trends are plotted on alog scale. One can see that all solutes ollowa similar pattern to a rst approximationbecause the dominant intermolecular orceo interaction is dispersive.There are slightdiferences in slopes or homologs withdiferent unctionalities.These arise rompolar interactions and will be discussed nextmonth.

References

1. J. D. van der Waals, The Thermodynamic Theory o Capillarity

Under the Hypothesis o a Continuous Variation o Density,

originally published in Dutch in Verhandel. Konink. Akad. Weten.

Amsterdam, 1, 8, (1893)

2. Von R. Eisenschitz, F. London, ber das Verhltnis der van der

Waalsschen Krte zu den Homopolaren Bindungskrten Z.

Physik, 60, 491-527, (1930)3. W. H. Keesom, On the Deduction o the Equation o State

From Boltzmanns Entropy Principle, Communications

Physical Laboratory University o Leiden Supplement, Ed. By H.

Kamerlingh Onnes, Eduard Ijdo Printer, Leiden, Supplement 24a

to No. 121-132, 3-2. 0, (1912)

4. P. J. W. Debye, Die van der Waalsschen Kohsionskrte,

Physik. Zeitschr., 21, 178-87, (1920)

Dr Matthew S. Klee is internationally recognizedfor contributions to the theory and practice of gaschromatography. His experience in chemical, pharmaceutical

and instrument companies spans over 30 years. During thistime, Dr Klees work has focused on elucidation and practicaldemonstration of the many processes involved with GCanalysis, with the ultimate goal of improving the ease of useof GC systems, ruggedness of methods and overall quality ofresults.

Figure 4: Intermolecular interactions between a solute and a stationary phase lead to retention.

Retention o solutes is an exponential unction o temperature.Retention decreases by orapproximately every 23 oC change in temperature (solute and stationary phase dependent).

Figure 5: The exponential retention unction o several solutes plotted on log scale. More volatile solutes(e.g., solute B) will elute earlier and at lower temperatures in a temperature programmed run.To a rstapproximation, or a polar stationary phases the dependence o retention on temperature ollows the

same trend or all solutes because o dominance o dispersive (non-polar) orces o interaction,

diferences in slopes arise rom diferences in solute polarities (e.g., solutes A and C). Homologs usuallyhave the the same retention vs temperature slope on a given stationary phase (e.g., solutes B and D).


6/9

Featured Applications

Automated Static and Dynamic Headspace Analysis with GC-MS for Determination of Abundantand Trace Flavour Compounds in Alcoholic Beverages Containing Dry ExtractCompany: Gerstel

In this application note a combination o static and dynamic headspace analysis is described orproling both abundant and trace compounds in these products. Static headspace is used witha tenax packed injection port liner or the abundant compounds. Dynamic headspace uses an

additional purging step to a second tenax liner which can then be desorbed to the same injection port linerused or the simple static headspace. In this case the previous abundant compounds are overloaded in thechromatogram but many additional trace compounds are now apparent.

Analysis of Butylated Hydroxytoluene in Food with Headspace Trap-GC/MSCompany: PerkinElmer

This application note will demonstrate a ast and easy analytical technique to determine theamount o BHT in oods. Headspace sample introduction is used because it provides a means toanalyse ood without any sample preparation. Headspace eliminates the need or solvents andother sample preparation steps to reduce cost and complexity o extraction. In this method, an

adsorbent trap is used to concentrate the headspace sample and increase sensitivity, allowing or low-leveldetection or small sample sizes.

Determination of 2,4,6 Trichloroanisole in Cork and Wine with HS-SPME/GCMSCompany: Shimadzu

Cork stoppers used or wine bottles can aect the taste o the wine. The main contaminant isthe well known 2,4,6-Trichloroanisole. This is an o-favour which is believed to be produced bymethylation o phenols o the cork tree and nal bleaching o the cork. Human nose and taste cantrace back down to about 5-10 ng/L (5-10 ppt). For the quality control o cork stoppers thereore an

enrichment technique such as solid phase microextraction (SPME) is needed. Then the analysis with GC-ECD orGCMS is perormed. Here the result obtained with GCMS are reported.

AppNote3/2010 Automated Static and DynamicHeadspace Analysiswith GC-MS

forDetermination ofAbundantandTrace FlavourCompoundsin AlcoholicBeveragesContaining DryExtract

Kevin Mac Namara,Frank McGuiganIrish Disti l lers-Pernod Ricard, Midleton Disti l lery, Midleton, Cork,Ireland

Andreas HoffmannGerstelGmbH&Co.KG, Eberhard-Gerstel-Platz1,D-45473 Mlheiman derRuhr, Germany

KEYWORDS

PTV injection, Static headspace, Dynamic headspace,Alcoholicbeverages

ABSTRACT

Directinjectionforgaschromatographicprofilingofalcoholicbeveragesisusuallypreferable,butwherespiritsandliquorscontain appreciableamountsofnon-volatilematerial, somemodeofpre-treatmentmayberequired to avoid both inletand column contamination. This consideration applies in

particularto productsaged forextended periodsin woodenbarrels and especially products containing added sugar,as volatile artefacts from sugar decomposition in the hotinjection portcan also complicatethechromatogram.

In this paper a combination of static and dynamicheadspaceanalysisisdescribed forprofiling both abundantand tracecompoundsin theseproducts. Staticheadspaceisusedwithatenaxpackedinjectionportlinerfortheabundantcompounds. Dynamicheadspaceusesan additionalpurgingstep to a second tenax liner which can then be desorbedto thesameinjection portlinerused forthesimplestaticheadspace. In thiscasethepreviousabundantcompoundsareoverloaded in the chromatogrambutmanyadditionaltracecompoundsarenowapparent. Forboth techniquesthe

Download

Introduction

Butylated hydroxytoluene(BHT, 2,6-di-tert-butyl-4-methylphenol)is a common food additive. BHT is foundin many types of food including butter,meats, cereals, chewing gum, bakedgoods, snack foods, dehydrated potatoes

and beverages. It is used to preserve foododor, color and flavor. BHT is oxidizedpreferentially in fats or oils, protectingthe foods from spoilage.

Concern exists that long-term human consumption of BHT may have potentialhealth risks. It has undergone the additive application and review processrequired bythe U.S.Food and Drug Admini stration (FDA);the committee concludedthat no evidence in the available information on BHT demonstrates a hazard tothe public when it is used at levels that are now current and in the manner nowpracticed. However, uncertainties exist requiring that additional studies shouldbe conducted.1 The chemical properties which make BHT an excellentpreservativemay also be implicated in health effects. The oxidative characteristics andmetabolites of BHT may contribute to carcinogenicity. Some people may havedifficulty metabolizing BHT, resulting in health and behavioral changes.

Gas Chromatography/

Mass Spectrometry

a p p li ca t i on n ot e

Author

Meng Yuan

Perki nElmer,Inc.

Shelton,CT 06484 USA

Analysis of ButylatedHydroxytoluene inFoodwithHeadspaceTrap-GC/MS

Download

SCA_280_065 www.shimadzu.de

ApplicationNote

Determination of 2,4,6Trichloroanisolein corkand winewith HS-SPME/GCMS

-standard

- f a st

Corkstoppersusedforwinebottlescaneffectthetasteofthe wine.Themaincontaminantisthewellknown2,4,6-Trichloroanisole.Thisisanoff-flavorwhichisbelievedtobe producedbymethylationofphenolsoft hecorktreeandfinalbleachingofthecork.Human noseandtastecantracebackdowntoabout 5-10ng/L(5-10ppt).Forthequalitycontrol ofcorkstoppersthereforeanenrichmenttechniquelikesolidphasemicroextraction(SPME)isneeded.ThentheanalysiswithGC-ECDorGCMSisperformed.Heretheresultobtained

withGCMSarereported.Before the headspace SPME is done a l iquidextraction was performed with the corks. Forthis the corkstoppers were put into a 2 Lethanol water solution (12 %) for 24 hours atroomtemperature. Then an aliquot of 10 mlwere put into a 20 ml headspace vialsaturated with 3 g NaCl. The latter increasesthe effectivity of the adsorption of the TCAonto the fiber. As an internal standard adeuterized TCA is added ( 2H5-2,4,6-TCA).With these vials the automatized headspace-SPME experiments were performed using apolydimethylsiloxane fiber (PDMS, Supelco).The instrument used was a GCMS-QP2010with an AOC-5000 autosampler. In figure 1the incubatorof the AOC-5000 is shownwhen the headspace vial is placed into it.

Fig.1:20mlHeadspacevial placedintoincubatorof theAOC-5000

For the method optimization in a first step aliquid standard was injected. In the secondstep the liquid extract prepared a statedabove was spiked with TCA. To havemaximumintensity theMS was runinselected ionmonitoring (SIM).

6 . 0 7 . 0 8 . 0 9 . 0 1 0 . 0 1 1 . 0 1 2 . 0 1 3 .0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0( x10,000)

Fig.2:Top:SIM 1) dataofmasstrace195 relativetoanextractspikedwith17ppt TCAcomparedwithanunspikedextract.

In figure 2 the SIM data of an extract spikedwith 17 ppt compared to the blank extract isshown clearly indicating the 195 amu tracerelative to the 2,4,6, TCA which was used asthe quantifier ion. Qualifier ions usedwere210 and 212.The SPME parameters were:Extractiontemperature and time 50 C 30 min,desorption at 220 C for 2 min.The analysis conditions used for the GCMSwere: Injection splitless 2 min with highpressure pulse at 200 Kpa, Column: TRB 525 m, 0.25 mm, 0.25 m,5 0 C 2 mi n ,12C/min138C3 min20C/min260 2min linear velocity of the carrier gas 48.2cm/s, interface temperature: 270C.As a quantifier ion for the D-TCA the masstrace of 215 was used. Figure 3 shows thezoomed mass trace of 195 and 215 relativ toa standard of 0.7 ppt. The peak of the 2,4,6TCA is still clearly visible. The calibrationcurve is alsoshown in that figure.

SIM

trace1952,4,6 TCA

Download


7/9

Automatic Detection o Trace Target Compounds in Complex Chemical Emission Profles romProducts and MaterialsCompany: Markes International

Under new regulations, manuacturers o construction products and consumer goods areresponsible or identiying and measuring any dangerous chemicals which could be emitted(released) by their products under normal use. Testing chemical emissions rom products usually

involves placing product samples in environmental chambers, or micro-chambers, with subsequent vapoursampling onto sorbent tubes and thermal desorption (TD)GC/MS analysis. An advanced sotware package hasbeen developed as an automated tool or interpretation o complex total ion chromatographic (TIC) data.

Detecting Drugs o Abuse: Enhanced Identifcation Using Benchto-dx and Associated SotwareCompany: ALMSCO

In this study, a urine sample was obtained or DOA analysis. Fast GC was perormed with MSdetection using the BenchTOF-dx. The instruments associated sotware incorporates background-compensation, deconvolution and data-mining which enhance and automate the identication otarget compounds in very convoluted data. In the sotware, a spectral library o the compounds o

interest is compiled and the total ion chromatogram (TIC) o the urine sample is searched or matching spectra.The capabilities o this sotware are enhanced by the high quality spectra produced by the BenchTOF-dx.

Food Decomposition Analysis Using the Micro-Chamber/Thermal Extractor and TD-GC/MSCompany: Markes International

The shel lie o ood products is o huge interest to the ood industry. The main actor governing theperiod o shel lie is the rate o decomposition. As ood decomposes, the emission prole changessuch that the desirable favour compounds diminish while unavourable o-odours and hazardous

compounds are emitted. Valuable inormation regarding the rate o decomposition and release oundesirable compounds can be obtained by sampling and analysing the vapours emitted by a product overtime. This note describes the application o a Micro- Chamber/Thermal Extractor (-CTE), compact dynamicheadspace extraction instrument, which allows accurate control o an atmosphere and extraction o emissionsrom multiple samples simultaneously.

WWW.ALMSCO.COMGwaun ElaiMediScienceCampus| Llantrisant | RCT | CF728XL| United Kingdom

T:+44(0)1443233920| F:+44(0)1443231531| E:[email protected]

Introduction

Whenscreeningurine for drugsof abuse(DOA), reliabilityiscrucial. Detectionofcompoundssuchasmarijuana, cocaine,heroinand amphetamines, aswellastheir metabolites, iscommonlycarriedout byGC/MS, however the complexityof asample suchasurine canpresent ananalyticalchallenge. Highmatrixeffectsand frequent co-elutioncansignicantlycompromise reliabilityof identication,particularlyfor DOA at trace level,therefore these factorsneed tobeaddressed.

Traditionallyused quadrupole MSsystemsare signicantlyrestricted intermsof sensitivitywhenused forscreening(i.e .inscanmode)and spectraobtained are commonlyaffected bythephenomenonof spectralskew, resultinginfalse-positive or -negative results.Increased sensitivitymaybe provided inSIMmode, however whole samplescreeningisnot viable asthe number ofcompoundsidentiable isverylimited.

Additionally, the identicationof certainpolar drugsof abuse usingGC/MS hashistoricallynecessitated derivatisation.

It isthese limitationsthat require ascreeningtechnique that offershighsensitivityand qualityspectraldatafor allcompounds, includingtrace-level,regardlessof sample complexity.

Of late, increasingattentionhasbeendrawntomoderntime-of-ight (TOF)MSinstrumentsasapotentialsolutiontocomplexmixture screening. New systemsare able toacquire dataover averywidemassrange at veryfast scanrates. Theserobust instrumentsare achievingpopularitydue towell-documented highlevelsof sensitivity. However, asignicantdrawbackof TOF MS systemstodate hasbeenthe generationof spectrathat donot resemble quadrupole-acquiredspectra. Thismeansusers existingorcommerciallyavailable (e.g. NIST)librariesare not applicable for compoundidentication, necessitatingthe laboriousand undesirable creationof bespoke,TOF-specic spectrallibraries.

The recently-introduced BenchTOF-dxTOF MS (Figure 1) , however,demonstratesbreakthroughcapabilitytoprovide exceptionalsensitivityinadditiontospectrathat exactlymatchclassical, quadrupole-generated spectra,resultingfromveryhighdataacquisitionspeeds(up to10,000Hz; 560spectra/second). Identicationusingestablished or commerciallyavailable,librariesistherefore possible, ensuringspeed and accuracyof results.

Inthisstudy, aurine sample wasobtained for DOA analysis. Fast GCwasperformed withMS detectionusingtheBenchTOF-dx. The instrumentsassociated software incorporatesbackground-compensation,deconvolutionand data-miningwhichenhance and automate the identicationof target compoundsinveryconvoluteddata. Inthe software, aspectrallibraryofthe compoundsof interest iscompiledand the totalionchromatogram(TIC)ofthe urine sample issearched formatchingspectra. The capabilitiesof thissoftware are enhanced bythe highqualityspectraproduced bytheBenchTOF-dx.

Experimental

A urine sample wascollected fromamethadone substitutionprogramme.Glucuronide separationwasfollowed bysorptive extraction(SPE)usingSPECDAUcationexchangerstoextract the organiccompoundsfromthe urine. SPE isahighlyselective and sensitive techniquefor samplingvolatile compounds(suchasDOA)fromaqueousmatrices.

Application Note: ANBT12

Detecting drugsof abuse: Enhancedidentification usingBenchTOF-dx andassociatedsoftware

Figure 1. The BenchTOF-dxtim e-of-ightm ass spectrom eterfrom A LMSCOInternational

TD TS

www.markes.com

MarkesInternational Ltd T:+44 (0)1443 230935 F: +44 (0)1443 231531 E:[email protected]

I n t r o d u c t i o n Theshelf lifeof foodp roducts is of huge interest to the

foodindustry. The main factorgovern ingtheper iodof

shelf lifeis therateof decomposition . As food

decomposes, theemission profilechanges suchthat the

desirable flavourcompounds dimin ishwhileunfavourable

off-odours andhazardous compounds areemitted.

Valuableinformation regardingtherateof decomposition

andrelease of undesirablecompounds can beobtained

bysamplingandanalysingtheva pours emittedbya

product overtime. Markes Internationals Micro-

Chamber/ThermalExtractor(-CTE)provides industry

withacompact dynamic headspaceextraction

instrument, whichallows accuratecontrolof an

atmosphereandextraction of emissions frommultiple

samples simultaneously.

The-CTE has been designedforsimplifieddynamic

headspacesamplingof product emissions withmin imal

samplepreparation. Two versions of the-CTE are

manufacturedbyMarkes; onecompr isingfour individual

chambers of 114mLcapacityandone compr isingsix

chambers of 44mLcapacity(figure1). Allchambers are

inert-coatedstain less steelto min imisesink effects and

aidtherecoveryof veryreactivespecies. Samples

includingfoods, dr inks, ingredients, packaging, etc. may

beplacedintot heindividualchambers within theunit,

incubatedat aselectedtemperatureand purgedwitha

constant flowof pureairor inert gas.

Followingan equilibration per iod, clean sorbent tubes are

connectedtotheoutlet of eachindividualmicro-chamber

tocollect theorganic vapours purgedfromthesample in

theflowof pureairorgas. Sorbents maybechosen to

retain allemittedheadspacevapours or toselectively

retain keyolfactorycompounds whilepotential

in ter ferences suchas water , ethanoloracetic acidare

purgedtovent. Thesorbent tubes aresubsequently

analysedbythermaldesorption (TD)withGC(MS).

TDis aGC-specific sampleconcentration techniqueused

tosign ificantlyincreasethesensitivity of organic

analysis. Markes leading-edgeTDtechnologybenefits

fromseveralkeyinnovations pioneeredbyMarkes

Internationaloverrecent years. Examples relevant tothis

application include:

Compatibilitywith everyTDapplication (including

reactivespecies; amines, thiols, etc.)usingasingle

valve/flowpathconfiguration.

Thea bilitytoquantitativelyre-collect samples for

repeat analysis andmethodvalidation. Availableon

manualandautomatedmodels.

Wor lds most effectivecryogen-freefocusingoffers

maximumuptime(nor isk of iceblockage)without

compromisingretention of u ltra-volatiles.

Efficient backflushdesorption of thesorbent tube

andfocusingtrapoffers simultaneous analysis of

compounds overawideboilingrange combined

withoptimumsensitivity.

Forfurther information seeMarkes Ser ies 2UNITY and

TD-100 brochures.

igure 1 he icro- h m er/herml xtr ctor (- )un its

Thermal DesorptionTechnical Support

Note95:Fooddecompositionanalysisusingthe

Micro-Chamber/ThermalExtractorandTD-GC/MS

Keywords:

VOC,food,flavour,fragrance,dynamicheadspace,shelf life

TDTS Thermal DesorptionTechnical Support

www.markes.com

MarkesInternational Ltd. T:+44 (0)1443 230935 F: +44 (0)1443 231531 E:[email protected]

B a c k g r o u n dUndernewregulations, manufacturers of construction

products andconsumergoods areresponsiblefor

identifyingandmeasur inganydangerous chemicals

whichcouldbeemitted (released)bytheirproducts

undernormaluse. This is tomakesurethat theydont

posear isk toconsumers. Thetoxic andodorous

chemicals of in terest arespecifiedin standardprotocols

andinclude awiderangeof volatileandsemi-volatile

organic compounds ([S]VOCs).

Thesenewregulations aredr ivingindustrytoimplement

chemicalemissions testingin -house, bothforquality

control(QC)andforresearchand development (R&D).

Testingchemicalemissions fromproducts usually

involves placingproduct samples in environmental

chambers, ormicro-chambers, withsubsequent vapour

samplingontosorbent tubes andthermaldesorption

(TD)GC/MSanalysis. Theemission profiles yieldedfrom

aproduct ormater ialcan becomplex andcontain many

target compounds at tracelevels. This makes themtime

consuminganddifficu lt tointerpret correctly, particu lar ly

in abusyindustr ialQClaboratory.

An advancedsoftware package (TargetView; ALMSCO

International, adivision of Markes)has been developed

as an automatedtoolfor interpretation of complex total

ion chromatographic (TIC)data. sophisticated

chemometr ics, TargetViewis abletoidentifyt arget

compounds ( g . thosefromaregulatorylist )withincomplex GC/MSchromatograms.

Introduction toTargetView

TargetViewhas been designedpr imar ilyforease-of-use,

allowingnon-experts toanalyzeemission profiles from

real-wor ldsamples. However , it can alsobeusedto

enhanceandspeed-updetailedemission profileanalysis

forresearchpurposes.

TooperateTargetView, theGC/MSdatafileis simply

importedinto thesoftwarepost-run andreprocessed.

Thesoftwarecan beconfiguredtosearchfo rmultiple

target compounds within alibraryandis availablepre-

programmedwithtarget librar ies foremission testing

(e . AgBB1/AFSSET2 LCI [lowest concentrations ofin terest]compounds orCaliforn ia013503 CREL [chronic

referenceexposurelevels]compounds). Ultimately, a

simplereport is producedforeachsample, listingall

target components identifiedin the emission profile.

TargetViewis compatiblewithavar ietyof commercial

GC/MSfileformats. It works byapplyingsophisticated

chemometr ic processes to thedata. Firstly, it selectively

eliminates anybackground, (water/airoffset, column

bleed, .), fromtheTICusingdynamic background

compensation (DBC). Figure1shows acompar ison of

therawdataa ndtheDBC-reprocesseddata. Theprocess

of backgroundcompensation eliminates inter fer ing

backgroundions fromthespectraof the

chromatographic peaks. Theenhancedspectralpur ity

andflatterbaselineof thereprocesseddata facilitate

efficient data-min ingandcompoundidentification bythe

subsequent stages of TargetView.

Notethat TargetViewcreates asecondreprocessedfile

foreachsample. Theor iginaldatafile is left in tact

(without backgroundcompensation)andavailable for

calcu lations suchas TVOCdetermination, if required.

Thespectraof co-elutingpeaks arethen deconvoluted,

allowingeachindividualmass ion tobeassignedto the

appropr iatecompound. Pr incipalcomponent analysis

(PCA; e . pattern recognition)is then appliedtothedeconvolutedspectratoide ntifyanycompounds in the

samplewhichmatchta rget components in thelibrary.

Amatchco-efficient is calcu lated(01), andcompounds

withaco-efficient belowaspecified value( e . g . 0.9)canbeeliminatedtoenhance confidence in theresults.

Thesehits arethen listedin asimplereport format.

Note90:Automaticdetectionoftracetargetcompoundsincomplexchemicalemissionprofilesfromproductsand

materials

Keywords:

Chemical release,productemissions,plasterboard,mahogany,childrens toys,trace analysis,targetcompounds

Download

Download

Download


8/9

Products

GC Pressure and Flow Calculations iPhone/iPod ApplicationCompany: Agilent

Manufacturers description: Agilent has developeda GC pressure and fow rate calculator app or theiPhone/iPod to instantly and accurately determinepressure and fow through open tubular capillarycolumns. The Agilent GC Calculator app is based onthe PC version that has been downloaded more than 10,000 times rom theAgilent website. The GC calculator enables you to:

See how dierent GC conditions aect column fow and pressure beoresetting up a system

Determine i your current column dimensions are appropriate and/orwhat your inlet pressure should be when switching rom GC (atmosphericpressure) to GC/MS (vacuum)

Calculate new parameters when switching to a dierent carrier gas, suchas going rom helium to hydrogen or aster chromatography

Predict hold-up times during troubleshooting Check i your inlet can handle higher pressures associated with narrow

bore capillary columns

For more information, click here

For information on how to use the app, click here

Agilent GC Calculator works with iPhone 4, iPhone 3G, the original iPhone, and iPod touch.

Apple, the Apple logo, iPod, iPod touch, and iTunes are trademarks o Apple Inc., registered in the U.S. and other

countries. iPhone is a trademark o Apple Inc. App Store is a service mark o Apple Inc.

Separation of Drugs of AbuseCompany: Phenomenex

Manufacturers description: Available rom Phenomenex is an optimizedphase or the separation o drugs o abuse. The Zebron ZB-Drug-1column provides at least 30% aster run times than existing technologiesand delivers improved resolution o target analytes, according to themanuacturer. Zebron ZB-Drug-1 is a mid-polarity stationary phase thatseparates target analytes rom the common matrix intererences ound inbiological samples. Reported eatures o the column include:

Fast analysis with good peak shape

Specially deactivated to improve quantication for drug compounds Improved resolution of target analytes from matrix interferences

For more information, visit www.phenomenex.com


9/9

Advanced Topics in Capillary Gas Chromatography

Getting More from your GC3-4 November, 2010

Venue: Park Inn Manchester, Victoria, UK

Matthew Klees

GC Masterclass

CLICK HERE TO

REGISTER ONLINE

www.sepscience.com

2 day

695

Day 1

1. Capillary GC tune-up

2. Large volume injection

3. Auxiliary sampling and ocusing4. Fast GC how to painlessly and quickly migrate your current methods

Day 2

1. Multidimensional separations (instrumentation, practice)

2. Capillary column backfushing BF with benets

3. Automated sample preparation

4. Optimal mass spec.

5. Method development and troubleshooting - interactive discussion

Basis of NonPolar Interactions_GC Columns PI

Documents

Transcript of Basis of NonPolar Interactions_GC Columns PI