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Air Monitoring

Passive (Diffusive) Sampling Overview


Overview
Radiello Passive Sampling Products
DSD-DNPH Passive Sampling Device
Diffusion Caps for PerkinElmer® Thermal Desorption Tubes
SPME-Diffusive Sampling Fiber Holder (DFH)

Overview  

Passive or diffusive sampling relies on the unassisted molecular diffusion of gaseous agents (analytes) through a diffusive surface onto an adsorbent. Unlike active (pumped) sampling, passive samplers require no electricity (expensive pumps), have no moving parts, and are simple to use (no pump operation or calibration). After sampling, the adsorbed analytes are desorbed off the adsorbent by solvent or thermal desorption.

Benefits of passive/diffusive sampling:

  • Compact, portable, unobtrusive, and inexpensive
  • Offers indication of average pollution levels over time periods of 8 hours to weeks/months
  • Requires no supervision, is noiseless and can be used in hazardous environments
  • Low cost allows for sampling at multiple locations (e.g., for highlighting pollution "hotspots"; or determining long term data trends in a specific geographical area)
  • Amenable to personal monitoring (breathing zone), indoor air analysis, and outdoor ambient air analysis

From Fick’s Law, we know that the sampling rate (Q) is a function of the diffusion coefficient of a given analyte (D) and the geometric constant of the sampler (K): Q = D.K. The diffusion coefficient (D) always remains constant for a given analyte; therefore, to improve sampling rate (Q), the geometric constant (K) must be improved: K = S/l where S is diffusive surface and l is the distance between the diffusive and adsorbing surface.

Most commercially available passive/diffusive samplers are planar or axial in shape and offer lower sampling rates and limited sampling capacity. As a result, sensitivity can suffer during short-term analysis (due to low sampling rates), or long-term sampling (analyte back-diffusion due to low capacity). A radial coaxial design circumvents these issues by improving the geometry.

diffusion process Axial Sampler vs. Radial Sampler

In the mid 1990's a passive sampler with a revolutionary radial symmetry design was developed, and is now marketed as radiello®. Visit the radiello Center to learn more about applications and ordering information for this diffusive air sampling product line.


Our new DSD-DNPH Sampling Device is a high-efficiency diffusive sampler developed specifically for the determination of aldehydes and ketones in indoor air.



SPME-Diffusive Fiber Holder (DFH)

DFHfor TWA Air Sampling with SPME

A SPME-Diffusive Fiber Holder (DFH) installed with a SPME-FFA is capable of determining time-weighted average (TWA) concentration of volatile organic compounds (VOCs) in air. Unlike conventional sampling with SPME, in which a fiber is extended outside its piercing needle, during TWA passive sampling the fiber is retracted at a known distance into the needle. The SPME-DFH functions this way as a passive device. To read more click here.

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