Sampling Airborne VOCs with radiello Diffusive Samplers

Sampling Airborne VOCs with radiello Diffusive

Samplers

Jason S. Herrington, Ph.D.

Goal of Today’s Webinar

• Successfully answer some of the 5 “W” and 1 “H” questions pertaining to radiello:– What is radiello?– How does radiello work?– Who may benefit from radiello?– When can radiello be used?– Where is radiello unique?– Why is radiello better than alternatives?

Why Sample Airborne VOCs

• Volatile organic compounds (VOCs) are produced from both primary and secondary sources.

• Primary sources, either natural or anthropogenic, are directly emitted from the source to the air, while secondary sources result from atmospheric reactions.

• VOCs are ubiquitous in indoor, outdoor, and personal air.

How VOCs Impact Health

• Average adult inhales ~ 7 to 8 L/min = ~11,000 L/day

• VOCs and their atmospheric reaction products have well known adverse environmental impacts and detrimental human health effects.

• Assessing indoor, outdoor, and personal concentrations of VOCs has become almost as ubiquitous as some of the compounds of interest.

VOC Sampling

• Real-time Approaches– Instantaneous/Continuous Concentrations

• Online Gas Chromatograph (GC)– Flame Ionization Detector (FID)– Mass Spectrometer (MS)

• Photo Ionization Detector (PID)• Ultraviolet Doppler Optical Absorption Spectroscopy (UV-DOAS)• Open Path - Fourier Transform Infrared (OP-FTIR)

VOC Sampling (cont’d)

• Time Integrated Approaches – Whole Air (Everything Airborne is Collected)

• Bags• Canisters

– “In Field Concentration” (Depends on Sorbent Strength)• Active Sampling

– Solvent and Thermal Desorption (TD) Tubes

• Passive Diffusive– Badges– Tubes – radiello

“In Field Concentration” with Active Sorbent Sampling

• Requires a pumping devices to actively pass air sample across sorbent

• Advantages:– Generally considered environmentally

independent (i.e., temperature and humidity are less concerning)

– Accurate and constant flow control– Higher flow rates to achieve shorter

sampling durations

Active Sorbent Sampling

• Disadvantages = pumps:– Require flow calibration– More user

knowledge/intervention– Require power– Generate noise– Tend to be heavy– Not suitable in

explosive/flammable environments

Passive (Diffusive) Sorbent Sampling

Passive (Diffusive) Sorbent Sampling

• No pumps!!!– No noise– No electricity requirements– Less weight– No calibration– No maintenance– No tubing

• Better subject acceptance• Simple deployment and retrieval• Suitable to explosive/flammable environments

Principles of Diffusive Sampling

• Sorbent (e.g., carbon) housed in a diffusion body

• Diffusive sampling relies on the kinetic energy of the gas molecules

• Molecules diffuse across a permeable membrane [diffusive surface (S)] and onto a adsorbing surface (A)

Principles of Diffusive Sampling (cont’d)

• Sorbent with low concentration acts as “sink” to trap molecules from high concentration outside

• Concentration gradient (i.e., high to low) across “diffusion gap (DG),” which acts like a pump

• Mathematically explained by Fick’s First Law of Diffusion

Fick’s First Law - 3M OVM Example - from Shields and Weschler, 1987

“Axial” Diffusive Samplers

• Everything discussed so far holds true for an “axial” type diffusive sampler

“Radial” Diffusive Samplers

• radiello is not an “axial” sampler. It is a “radial” type diffusive sampler

Diffusive Sampling with radiello

• The radius of radiello’s sorbent (ra) and the radius of the diffusive body (rd) mean the mathematical model changes a little

radiello Diffusive Membrane

• radiello’s diffusive membrane provides a tortuous path, which increases length relative to membrane thickness

All Diffusive Samplers

• Fick’s First Law allows for mathematical predictions of chemical uptake rates

• Does not apply to a tortuous path

• AND true sampling rates are impacted by:– Concentration– Air velocity– Temperature – Humidity

All Diffusive Samplers Require Empirical Determination of

Sampling Rates

radiello Sampling Rates (cont’d)

radiello Sampling Rates Determined with:

• Controlled concentration gas mixtures from 1 µg·m3 to 1,000 mg·m3

• Temperature control from -20 to 60 °C

• Relative humidity control from 5% to 100%

• Air speed variation from 0.1 to 10 m·s1

radiello Sampling Rates

• radiello is a certified instrument (EN 13528: 2002; EN 14662-4.5: 2005).

• radiello is validated to the Italian National Unification (UNI) EN 838 standard (Atmosphere in the working environment – Diffusive samplers for the determination of gases and vapors – requirements and test methods).

radiello Peace of Mind

• rad165 (aldehydes) - Sampling rate is invariant with humidity in the range 15-90% and with wind speed between 0.1 and 10 m·s1

• rad141 (1,3-butadiene) - Both temperature and relative humidity affect the sampling rate

• If the temperature drops to 5 °C, the bias is + 12.9% at 20% RH or -2.4% at 80% RH, compared to 20 °C and 50% RH

radiello Solutions

• A variety of diffusion bodies, sorbent cartridges, and accessories for various VOC sampling scenarios

Radiello Solutions (cont’d)Compounds of Interest Diffusive Body Cartridge Exposure Time Sample Stability Extraction Analysis Detection LimitAldehydes Blue (1201) 165 15 min - 7 day 60 Day @ 4 °C Acetonitrile LC-UV 0.1 µg/m3 for 7 dayGeneral VOCs White (120) 130 15 min - 30 day 6 Month Carbon Disulfide GC-FID 0.05 µg/m3 for 7 dayGeneral VOCs Yellow (1202) 145 8 hr - 14 day 6 Month Thermal GC-MS 0.01 µg/m3 for 7 dayNitrogen (NO2) and Sulfur Dioxides (SO2) Blue (1201) 166 7 day - 15 day 4 Month @ 4 °C Water Visible Spectrometry and IC 1 ppb for 7 day

Ozone (O3) Blue (1201) 172 8 hr - 14 day 7 Day MTBH Visible Spectrometry 2 µg/m3 for 7 day

Hydrogen Sulfide (H2S) Blue (1201) or White (120) 170 1 hr - 15 day 6 Month Water Visible Spectrometry 1 ppb for 24 hr

Ammonia (NH3) Blue (1201) or White (120) 168 1 hr - 14 day 12 Month Mixed Solution Visible Spectrometry 1 µg/m3 for 24 hrHydrochloric Acid (HCl) Blue (1201) or White (120) 169 15 min - 7 day 24 Month Water IC 10 µg/m3 for 24 hrHydrofluoric Acid (HF) Blue (1201) or White (120) 166 15 min - 14 day 4 Month @ 4 °C Water IC or Ion Selective Electrode 7 µg/m3 for 24 hrN2O, isoflurane, ethrane, halothane and sevorane Grey (1203) 132 1 hr - 8 hr 30 Day Water-Methanol GC-ECD and GC-MS NA

phenol, methylphenol and dimethylphenol White (120) 147 2 hr - 7 day Not Listed Thermal GC-MS 0.3 µg/m3

1,3-butadiene and isoprene Yellow (1202) 141 8 hr - 7 day 14 Day Thermal GC-MS 0.1 µg/m3 for 8 hr

How to Deploy radiello130

How to Deploy radiello130 (cont’d)

radiello Applications

• Indoor, outdoor, personal air• Fence line monitoring• Soil gas / Vapor intrusion• Anywhere there are VOCs of interest

How to Extract radiello130

How to Extract radiello130 (cont’d)

radiello Math

• rad 165 for acetaldehyde

• Atmosphere with 100 µg/m3 acetaldehyde for 15 minutes

84 mL/min15 min

1260 mL

100 µg/m³0.1 µg/L

0.0001 µg/ml

0.126 µg/cartridge

Acetaldehyde0.126 µg/cartridge

84 mL/min15 min

1260 mL

0.0001 µg/ml

100 µg/m³

Acetaldehyde

radiello Temperature Corrections

• rad 165 for acetaldehyde

• 20 °C instead of 25 °C84 mL/min @ 25 °C

293 K (20 °C)298 K (25°C)

0.983 ratio0.994 ratio ^ 0.35

83.5 mL/min @ 20 °C

Acetaldehyde

radiello AdvantagesSampler Benzene Uptake Rate

(mL/min)Capacity (mg)

TD Tube (Carbopack X) 0.67 NA

SKC Ultra 16 NA

3M OVM 36 22

radiello 80 80

• Increased uptake rate = shorter sampling durations OR increased sensitivity

• AND/OR increased capacity means longer sampling durations

Conclusions

• radiello is a passive (diffusive) sampler suitable for a wide variety of VOCs

• radiello has been rigorously tested at various concentrations, temperatures, humidities, and wind speeds

• radiello has higher uptake rates and capacity compared to competing technologies

Restek Resources – Technical Library

Restek Resources – Blog and FAQs

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Jason S. Herrington, [email protected]

Questions！