Solutions for monitoring VOCs in air

Transcription

1 Solutions for monitoring VOCs in air AQE, Telford 14 th March Nicola Watson Environmental Specialist Markes International

2 Agenda Sampling VOCs in air focusing on: Online/Canister sampling Monitoring ultra volatile compounds Sorbent tubes Passive sampling Active sampling Advanced mass spectrometry for air monitoring analyses

3 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 Extended More data points Laboratory demands Higher throughput Reduced maintenance Change in matrix Higher humidity, etc.

4 Air Monitoring Applications Include: Soil gas and vapour intrusion assessments Mapping criteria pollutants in ambient air, diurnal changes In situ monitoring of underground contamination Atmospheric Research

5 Air Monitoring Applications Include: Landfill gas monitoring Odorous industrial emissions Indoor air quality and tracer gases used for ventilation studies Biogenic emissions Hydraulic Fracturing

6 Thermal desorption One versatile technique for all vapour-phase air monitoring applications Electrically-cooled focusing trap Online Canisters/bags Sorbent tubes Passive Active Water and volatile interferences can be purged to vent Injection of µl vapour into GC(MS)

7 Application: Ultra volatile compounds Ethane Ethene Key: Blue (3 am) Red (12 noon) Green (5.30 pm) 1-Butene Acetylene 2-Methylpropene Pentane Propane Propene Butane 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 column Splitless analysis of 500 ml of ambient air

8 Online monitoring of odorous sulphur compounds in ambient & industrial air (UNITY-Air Server ) Target compounds: H 2 S (hydrogen sulphide) CH 3 SH (methanethiol/me.mercaptan) C 2 H 6 S (dimethyl sulphide) C 2 H 6 S 2 (dimethyl disulphide) Gas standards at 20 ppb and 10 ppb levels 3 channels with H 2 S 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

9 Application: Air toxics in canisters US EPA Method TO-15 1 L of a 1 ppb air toxics mix analysed splitless and cryogen-free using TD GC/MS scan

10 Canister air monitoring - Detecting perfluorocarbons Green house gas analysis

11 Can canisters do everything? Great for C 2 to C 12 compounds Suitable for rapid transfer (not storage) of ultra-volatile reactive compounds such as H 2 S Ideal for simple grab-sampling x NOT suitable for compounds with volatility less than C 10/12 x NOT suitable for high-concentration samples x Time-weighted average sampling is NOT easy with a canister

12 Application: Soil gas 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

13 Air monitoring Pumped Sorbent selection for both tubes and focusing trap are very important Semi-volatile compounds Weak sorbent Helps prevent retention of unwanted compounds Very volatile compounds Strong sorbent Prevents breakthrough of light compounds

14 Common sorbents Sorbent name Volatility range Water retention Quartz wool / silica beads C 30 C 40 Tenax TA C 7 C 30 Carbograph 2TD C 8 C 20 Carbograph 1TD C 5/6 C 14 Carbograph 5TD C 3/4 C 6/7 SulfiCarb C 3 C 8 Carboxen 1003 C 2 C 5 Carbosieve SIII C 2 C 5

15 Using sorbent tubes for diffusive sampling of outdoor air Mapping urban pollution concentrations with low-cost diffusive (passive) sampling 1 Black dots = 100 sampling sites Yellow dots = pollution hotspots 1 Application Note TDTS 10 Use of diffusive sampling with TD GC for ambient air monitoring

16 A complex example (US EPA TO-17) Splitless desorption of Air toxics tube loaded with 1 L of 1 ppb std GC/MS Source: Application Note TDTS 86

17 TD isn t just for trace levels: High-concentration industrial emission samples Re-analysis Re-analysis Sample 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

18 Sample security using sample re-collection Stage 1: Primary (tube) desorption with optional (inlet) split Heated valve To GC Intensity 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

19 Sample security using sample re-collection Stage 2: Secondary (trap) desorption with optional (outlet) split Heated valve To GC Intensity Time 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

20 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 Repeat 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 Original DEHP DDP

21 Not just volatiles... C 14 C 16 Benzene Re-collection C 18 Diethyl phthalate Dimethyl phthalate Dibutylphthalate Di-n-decyl phthalate C 20 C 24 C 28 C 32 C 36 C 40 Toluene Hexadecane Sample D-ethyl-hexyl phthalate Benzo(a)pyrene Re-collection Benzo(a)anthracene Chrysene Benzo(b)fluoranthene Benzo(k)fluoranthene Dibenzo(a,h)anthracene Indeno(1,2,3-cd)pyrene Benzo(g,h,i)perylene Sample PCB s Aroclor 1260 Re-collection Sample

22 BenchTOF-dx: Detector enhancements for air monitoring

23 What does BenchTOF-dx offer? Spectral accuracy cannot be compromised Sensitivity is KING Speed can be leveraged for deconvolution 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

24 Quadrupole comparison 500 ml sample of 4 ppb ozone precursor standard SIM (Quadrupole, 10 ions) Full scan (Quadrupole) Isoprene Time-of-flight (TIC) Detection method Full scan (Quad) S/N 15:1 SIM (Quad) 200:1 BenchTOF-dx 1500:1

25 Quadrupole comparison 200 ml sample of ambient rural air Quad data (magnified) Full scan and SIM (ten ions) BenchTOF-dx data (full spectrum)

26 Quadrupole comparison 200 ml sample of ambient rural air Quad data (magnified) full scan and SIM (ten ions) Carbon tetrachloride Atmospheric concentration ~100 ppt (~ 85 pg on column) Extracted ion 117 BenchTOF-dx data (TIC) Detection method Full scan (Quad) S/N ND SIM (Quad) 100:1 BenchTOF-dx 700:1

27 10 ml of ambient semi-rural air 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).

28 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 Higher splits, cleaner system but same MDLs However you want to! An investment in BenchTOF-dx provides a sensitivity boost!

29 Provides productivity too! Quad MS 1 ml injection of 1 ppm standard (62 component) with no split Equivalent to ~1000 ppt (1 ppb) on column 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!)

30 ...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) LODs (assuming 3:1 minimum S/N) 0.01 ppt (10 ppq) to 0.6 ppt (600 ppq) BenchTOF-dx at least 100 times better S/N than a quadrupole in full scan mode

31 ...whilst maintaining linearity R R R R R R R R R R R R R R

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

33 Any Questions? Nicola Watson Environmental Specialist Markes International