Paper Badges with Direct Indication

Although they have only been used in a limited number of cases, they have proved to give excellent results in special applications. For example, they are used in many plants and operations of the chemical industry for personal exposure monitoring of phosgene. Other examples include the determination of personal exposure doses of formaldehyde or ethylene oxide in clinical applications. 

When such impregnated papers are employed in combination with a motor-assisted continuous paper roll and coupled with a photometer and a data recorder, a system of continuous workplace monitoring can be established. This relatively simple measurement technique has proved of value for continuous monitoring of several industrial important diisocyanates, for instance toluene diisocyanate (TDI), methylene diisocyanate (MDI), isophorone diisocyanate (IPDI), naphthalene diisocyanate (NDI), and hexamethylene diisocyanate (HMDI). 

Furthermore, based on specific color reactions, indicator papers for the continuous measurement of ammonia, bromine, chlorine, hydrocyanic acid, hydrofluoric acid, ozone, phosgene, sulfur dioxide, and hydrogen sulfide are commercially available using photometric evaluation. Because of the often extremely intense coloration, detection hmits as low as the lower ppb range can be achieved by this method. Table 6.34 gives an overview of the range of determination and the detec- 

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The basic principle of reaction papers in the form of badges is very similar to that of the tubes. An agent is applied to a substrate, and the former undergoes a color reaction with the substance to be analyzed. The intensity of the discoloration correlates to the concentration of the air contaminant. The final evaluation can take place either by visual comparison with a calibrated color scale or by photometry. Figure 6.59 shows samples of badges with direct indications. 

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