Diffusion badges

Diffusion badges—used without pumps or batteries. Badges rely on solvent diffusion and results can be read directly in the field or via laboratory analysis. 

Diffusion badges—These can be used to confirm nondetectable levels. 

Passive diffusion sorbent badges are useful for screening and monitoring certain chemical exposures, especially vapors and gases. 

Recent Uses of Solid-Surface Luminescence Analysis in Environmental Analysis. Vo-Dinh and coworkers have shown very effectively how solid-surface luminescence techniques can be used for environmentally important samples (17-22). RTF has been used for the screening of ambient air particulate samples (17,18). In addition, RTF has been employed in conjunction with a ranking index to characterize polynuclear aromatic pollutants in environmental samples (19). A unique application of RTF reported recently is a personal dosimeter badge based on molecular diffusion and direct detection by RTF of polynuclear aromatic pollutants (20). The dosimeter is a pen-size device that does not require sample extraction prior to analysis. 

The badge sampling rate is a direct function of the diffusion coefficient (D) of the organic vapor(s) being sampled and the total cross-sectional area (A) of the badge cavities. The rate is an inverse function of the diffusion path or length (L) of the cavities. 

Badge-type or radial samplers which have a shorter diffusive path length but a high cross-sectional area. 

Badge samplers show greater uptake rates than tube-type samplers due to their greater cross-sectional area. This agrees with the given definition of uptake rate, which is directly proportional to the cross-sectional area and inversely proportional to the diffusive path length. 

As for workplace monitoring, there have been two main types of diffusive sampler used for monitoring of indoor air (i) badge type samplers containing a strong adsorbent such as charcoal that requires solvent desorption for GC analysis and (ii) tube type samplers with weaker adsorbents such as the porous polymer Tenax that can be thermally desorbed. The samplers most widely used have been developed for monitoring of workplace atmospheres and applied to indoor air through modification of the exposure period and the analytical method. 

The badge type samplers have higher diffusive uptake rates and, because strong sorbents are used, are not prone to reverse diffusion effects. They require solvent desorption (which is not easily automated) and the use of toxic solvents, and recovery of some compounds is poor. Contaminants in the solvent can reduce sensitivity as does the dilution effect typically 2 ml of solvent is used to desorb and 1 pi (i.e. 0.05 % of the collected mass of analyte) is used for GC analysis. 

The most widely used badge type sampler for indoor air studies has been the OVM 3500. This is a circular badge with a 1-cm diffusion length containing a charcoal wafer. Desorption of VOCs is carried out within the monitor itself by the addition of carbon disulfide. Exposure periods applied have ranged from 24 h to 3 weeks. The diffusive uptake rates reported by the manufacturer for 8-h exposure periods are about 30 ml/ min, but actual values are compound specific. For the monitoring of hexane in the workplace, the diffusive uptake rate is not significantly affected by ambient air movement, provided that there is a minimum air velocity of about 0.1 m/s (HSE, 1992). 

The solid sorbent diffusional dosimeter usually consists of a small badge-like container which can be attached to a worker or placed in an area for sampling. It is basically composed of a diffusion space or a group of spaces with a defined length to cross sectional area ratio. A porous wind screen may be used to define the opening and the solid sorbent, usually bound in a pad, is placed at the opposite end of the space. 

Figure 2 Types of diffusive samplers. From the left a colorimetric length-of-stain sampler a tube-type sampler for thermal desorption a badge-type sampler with multiple channels and no windscreen, containing a removable sorbent pad for solvent desorption a badge-type sampler with multiple channels and an internal windscreen, containing granular sorbent for in situ solvent desorption a badge-type sampler with an external vtrind-screen, behind which is an open diffusion path, and containing a sorbent pad for in situ solvent desorption.

In recent years passive samplers have become popular. They come with various kinds of analyte-specific sorbents, and the rate of diffusion for that particular device has been determined by the manufacturer. Some of these passive devices are color detector tubes and can be read directly after the sampling period. Other passive samples must be sent back to the supplier s laboratory for analyses. Figure 6.3.1.3 shows a passive sampling badge. 

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