Badge-type samplers

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). 

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.

One important consideration is the possibility of reuse of thermal desorption tubes, since they are cleaned in the desorption step. Charcoal badge-type samplers are of single-use nature but cheaper. Solvent desorption also allows multiple analyses from a single sample to give greater accuracy. 

Table 1 Compounds validated using the SKC Inc 575 series badge-type sampler with (A) charcoal and (B) Anasorb 747 sorbents...

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. 

The Gasbadge and OVM 3500 samplers were applied in a study of 230 homes in western Germany (Krause et al., 1987). The exposure period for both types of badge was 2 weeks, and 57 VOCs were determined. GC analyses were conducted with two fused silica capillary columns of different polarity, and detection was by simultaneous FID/ECD. During the course of the study the commercial manufacture of the Gasbadge monitor was discontinued. Table 1.5-2 shows results of a selection of the compounds monitored that includes compounds with both significant outdoor sources such as benzene from motor vehicle exhausts and indoor sources such as solvents containing undecane. 

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