Solutions for monitoring VOCs in air

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AQE, Telford 14th March

Nicola Watson

Environmental Specialist

Markes International

nwatson@markes.com

Agenda

• Sampling VOCs in air – focusing on:

– Online/Canister sampling

– Monitoring ultra volatile compounds

– Sorbent tubes

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– Sorbent tubes

– Passive sampling

– Active sampling

• Advanced mass spectrometry for air monitoring analyses

What (or who) drives new advances?

• Change in scope of monitoring

– Wider/smaller ranges of target compounds

– Lower levels

• Ambient Concentrations

• Regulatory Requirements

– Monitoring periods

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– Monitoring periods

• Extended

• More data points

• Laboratory demands

– Higher throughput

– Reduced maintenance

• Change in matrix

– Higher humidity, etc.

Air Monitoring Applications Include:

Soil gas and vapour intrusion assessments

Mapping criteria pollutants Mapping criteria pollutants in ambient air, diurnal in ambient air, diurnal changeschanges

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Atmospheric Research

In situ monitoring of underground contamination

Landfill gas monitoringOdorous industrial emissions

Air Monitoring Applications Include:www.markes.com

Indoor air quality and Indoor air quality and tracer gases used for tracer gases used for ventilation studiesventilation studies

Biogenic emissions

Hydraulic Hydraulic FracturingFracturing

Thermal desorption – One versatile technique for all vapour-phase air monitoring applications

Online

Canisters/bags

Electrically-cooled focusing trap

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Injection of 100–200 µL

vapour into GC(MS)

Water and volatileinterferences can be

purged to vent

Sorbent tubes

Passive

Active

Key:

Blue (3 am)

Red (12 noon)

Green (5.30 pm)

Ethane

Ethene

Acetylene

PropanePropene

2-Methylpropene

Butane

1-Butene

Pentane

Application: Ultra volatile compoundswww.markes.com

Quantitative retention of acetylene from 1500 mL of air

without liquid cryogen

Plot of peak area against volume

sampled for acetylene(courtesy of Ecole des Mines de Douai)

Sequence of analyses of ozone precursors in suburban air using a

single columnSplitless analysis of 500 mL of ambient air

Online monitoring of odorous sulphur compounds in ambient & industrial air (UNITY-Air Server™)

• Target compounds:

‒ H2S (hydrogen sulphide)

‒ CH3SH (methanethiol/me.mercaptan)

‒ C2H6S (dimethyl sulphide)

‒ C2H6S2 (dimethyl disulphide)

• 3 channels with ‘H2S’ focusing trap at -

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Gas standards at 20 ppb and 10 ppb levels

• 3 channels with ‘H2S’ focusing trap at -

15°C to -30ºC and flow path at 80ºC.

GC-PFPD

• Performance in field operation:

‒ Detection limits: 0.15 ppb

‒ Retention time stability: <0.1% RSD

across all compounds

‒ Standard reproducibility: 0.5-5% RSD

‒ Recovery: >87% for all analytes

Application: ‘Air toxics’ in canisters –US EPA Method TO-15

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1 L of a 1 ppb air

toxics mix

analysed splitless

and cryogen-free

using TD–GC/MS

scan

Canister air monitoring - Detecting perfluorocarbons

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Green house gas analysis

� Great for C2 to C12 compounds

� Suitable for rapid transfer (not storage) of ultra-volatile reactive compounds such as H2S

� Ideal for simple grab-sampling

Can canisters do everything?www.markes.com

x NOT suitable for compounds with volatility less than C10/12

x NOT suitable for high-concentration samples

x Time-weighted average sampling is NOT easy with a canister

Application: Soil gas www.markes.com

Profiles of soil gas contaminated with kerosene obtained using:

(a) Canister sampling and TO-15 analysis (blue)

(b) Sorbent tube sampling with TO-17 analysis (red)

Courtesy of H. Hayes, Eurofins Air Toxics, Folsom CA

Sorbent selection for both tubes and focusing trap are very important

Semi-volatile compounds – Weak sorbentHelps prevent retention of unwanted compounds

Air monitoring – Pumpedwww.markes.com

Very volatile compounds – Strong sorbentPrevents breakthrough of light compounds

Common sorbents

Sorbent name Volatility range

Quartz wool / silica beads C30 – C40

Tenax TA C7 – C30

Carbograph 2TD C8 – C20

Carbograph 1TD C – C

Water retention

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Carbograph 1TD C5/6 – C14

Carbograph 5TD C3/4 – C6/7

SulfiCarb C3 – C8

Carboxen 1003 C2 – C5

Carbosieve SIII C2 – C5

Using sorbent tubes for diffusive sampling of outdoor air

Mapping urban pollution concentrations with low-cost diffusive (passive) sampling1

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• Black dots = 100 sampling sites

• Yellow dots = pollution hotspots

1 Application Note TDTS 10 – Use of diffusive sampling with TD–GC for ambientair monitoring

A complex example (US EPA TO-17)www.markes.com

Source: Application Note TDTS 86

Splitless desorption of ‘Air toxics’ tube loaded with 1 L of 1 ppb stdGC/MS

TD isn’t just for trace levels: High-concentration industrial emission samples

Re-analysis

Re-analysis

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• Pumped sampling of 1 L stack gas with

TD-GC/MS analysis

• Sample splitting during both primary (tube)

and secondary (trap) desorption. Total split

ratio: 3000:1

• Quantitative re-collection of both splits

allows repeat analysis for confirmation

Sample

Heated valve

To GC

Sample security using sample re-collection

Inte

nsity

Stage 1: Primary (tube) desorption with optional (inlet) split

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To GC

• Patented heated valve is inert and low volume: Allows quantitative recovery of high and low volatility and reactive compounds

• The heated valve isolates the TD system allowing method compliance: leak testing, backflush trap desorption, purge to vent, overlap mode, etc.

Time

Inte

nsity

Heated valve

To GC

Inte

nsity

Stage 2: Secondary (trap) desorption with optional (outlet) split

Sample security using sample re-collectionwww.markes.com

To GC

Time

Inte

nsity

• Repeat analysis of re-collected samples makes it easy to

validate analyte recovery through the TD flow path

• A change to the overall VOC profile indicates any bias

Using Re-collection (SecureTD-Q™)Validation of routine methods Demonstrating quantitative

recovery of high boilers

• Repeat desorption of a mixed phthalate std –di-ethyl- to di-n-decylphthalate

• Repeat analysis shows quantitative recovery without bias, across the analyte range

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• 2 µL phthalate solution in methanol with 21:1 single split

• 20 re-collection, repeat analyses

• Good match between expected decay (lines) and observed decay (points)

• Demonstrates quantitative recovery

NB: ASTM Method D6196 references quantitative

re-collection for validation

DEHPDDPOriginal

Repeat

Not just volatiles....

C40C36

C32C28

C24C20

C18

C16C14

Dimethylphthalate

Diethyl phthalate

Dibutylphthalate

Di-n-decylphthalate

D-ethyl-hexylphthalate

Hexadecane

Toluene

Benzene Re-collection

Sample

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Be

nzo

(a)a

nth

racene

Re-collection

Sample

Re-collection

Sample

Ch

ryse

ne

Be

nzo

(b)f

luo

ran

then

e

Be

nzo

(k)f

luo

ran

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Benzo(a)pyreneIn

de

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(1,2

,3-c

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yre

ne

Be

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(g,h

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len

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Dibenzo(a,h)anthracene

PCB’s Aroclor 1260

BenchTOF-dx: Detector enhancements for air monitoring

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What does BenchTOF-dx offer?

• Spectral accuracy cannot be compromised

• Sensitivity is KING

• Speed can be leveraged for deconvolution

• Selectivity – enhanced mass resolution should

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• Selectivity – enhanced mass resolution should mainly be used to limit the matrix in VOC work(high res has limited advantages)

• Stability is key to productivity

SIM (Quadrupole, 10 ions)

Full scan (Quadrupole)

500 mL sample of 4 ppb ozone precursor standard

Quadrupole comparisonwww.markes.com

Isoprene

(Quadrupole)

Time-of-flight (TIC)

Detection method

S/N

Full scan (Quad)

15:1

SIM (Quad) 200:1

BenchTOF-dx 1500:1

Quad data (magnified) – Full scan and SIM (ten ions)

Quadrupole comparison

200 mL sample of ambient rural air

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BenchTOF-dx data(full spectrum)

Carbon tetrachloride

Atmospheric concentration~100 ppt (~ 85 pg on column)

Quad data (magnified) full scan and SIM(ten ions)

Quadrupole comparison

200 mL sample of ambient rural air

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Extracted ion 117

BenchTOF-dx data(TIC)

Detection method

S/N

Full scan (Quad) ND

SIM (Quad) 100:1

BenchTOF-dx 700:1

10 mL of ambient semi-rural airwww.markes.com

Total ion chromatogram showing splitless analysis of only 10 mL of semi-rural air

using TD–GC–TOF MS.

Inset: Extracted-ion chromatogram for a characteristic fragment ion of Freon® 113

(present in the atmosphere at ca. 80 ppt).

How can I use a large sensitivity boost in air

monitoring applications?

• Trace-level work for unknowns and targets combined at lower method detection limits (MDLs)

• Smaller sample sizes but same MDLs

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• Higher splits, cleaner system but same MDLs

• However you want to!

An investment in BenchTOF-dx provides a sensitivity boost!

Quad MS – 1 mL injection of 1 ppm standard

(62 component) with no split

Equivalent to ~1000 ppt (1 ppb) on column

Provides productivity too!www.markes.com

BenchTOF-dx – 1 mL injection of 1 ppm standard

(65 component) with 100:1 split

Equivalent to ~10 ppt (0.01 ppb) on column

From 40 minutes to 7 minutes (4 runs in the time to do 1!)

...without compromising sensitivity

BenchTOF-dx – 1 mL injection of 1 ppm standard (65 component) with 292:1 split

Equivalent to ~3 ppt (0.003 ppb) on-column

RMS signal-to-noise

ranges from

15:1 to 1350:1 (non DBC)

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BenchTOF-dx – at least 100 times better S/N than a quadrupole infull scan mode

(non DBC)

LODs (assuming 3:1

minimum S/N)

0.01 ppt (10 ppq) to0.6 ppt (600 ppq)

...whilst maintaining linearityR2 0.9996

R2 0.9995

R2 0.9995

R2 0.9993

R2 0.9992

R2 0.9990

R2 0.9990

R2 0.9990

R2 0.9989

R2 0.9989

R2 0.9988

R2 0.9985

R2 0.9984

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R2 0.9984

R2 0.9975

Summary

• A combination of canisters and sorbent tubes provides a comprehensive evaluation of an application, e.g. ambient air monitoring

• Markes specialist team can advise on sampling options that are suitable for your air/personal

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options that are suitable for your air/personal monitoring requirements

• BenchTOF-dx provides a sensitivity and productivity boost that can be utilised several ways while providing method tunes and NIST-compliant spectra

Any Questions?

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Nicola Watson

Environmental Specialist

Markes International

nwatson@markes.com