Passive or diffusive air 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
- Offer an indication of average pollution levels over time periods of 8 hours to weeks or months
- Require no supervision, 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)
- Suitable for personal monitoring (breathing zone), indoor air analysis, and outdoor ambient air analysis
PASSIVE/AMBIENT AIR SAMPLING USING RADIELLO
Radiello is an accurate, precise and certified instrument (EN 13528: 2002; EN 14662-4.5: 2005) that has no energy consumption, does not involve the use of heavy and bulky pumps, does not require surveillance, produces no noise, is suitable for flammable or explosive environments and can be used anywhere due to its simplicity. The diffusive surface is cylindrical rather than flat, as in traditional axial diffusive samplers, and the adsorbent is contained within a coaxial cylindrical system.
THE COMPONENTS OF RADIELLO
The essential parts of radiello are the adsorbing cartridge, the diffusive body, the supporting plate and the adhesive label with the bar code indication. Apart from the adsorbing cartridge, if not differently stated, all of the other components can be used for a lot of sampling experiments.
The adsorbing cartridge
Depending on the polluting compound to be sampled, several different kinds of adsorbing or chemiadsorbing cartridges have been developed. They are contained in glass or plastic tubes wrapped up in a transparent polyethylene thermowelded bag. The code number, printed onto the bag along with the lot number and expiry date indicates the kind of cartridge. The cartridge has to be introduced into the diffusive body.
The diffusive body
There are 4 kinds of diffusive bodies are available.
- The white diffusive body, code 120, of general use, is made of microporous polyethylene 1.7 mm thick and average porosity 25 ± 5 µm. Diffusive path length is 18 mm.
- The blue diffusive body, code 120-1, has the same properties of the white one but is opaque to light: it is suited to the sampling of light-sensitive compounds.
- The yellow diffusive body, code 120-2, should be used whenever the sampling rate must be reduced; it is made of microporous polyethylene 5 mm thick and average porosity 10 ± 2 µm. Diffusive path length is 150 mm.
- The permeative diffusive body, code 120-3, is a 50 µm thick silicone membrane strengthened by a stainless-steel net. It is employed for anaesthetic gases and vapours sampling.
The diffusive body must be screwed onto the supporting plate.
The supporting plate
Made of polycarbonate, it acts both as closure and support for the diffusive body, which must be screwed onto the thread. It comes along with a clip and a transparent adhesive pocket to hold the label. The three parts are to be assembled before use.
Self-adhesive, with printed barcode number. Since each barcode number has been printed in only one copy, it allows an unmistakable identification of the sampling tube on field and in the laboratory for the subsequent analysis.
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