Abstract
One of the oldest and simplest methods for analysis of chemicals is through the development of color as used, for example, in determining the end point of titrations. Chemicals that change color in response to the presence of another chemical species lend themselves to rapid and simple field analyses, of which the most basic method is the use of litmus paper. Gradual changes in color with concentration can be compared to standards simply by eye, or by means of an instrumental color comparator, spectrophotometer, or densitometer. This equipment is uncomplicated, relatively cheap, and portable, and the costs of field measurements using these techniques compare favorably with those that involve sampling followed by laboratory analysis. Since access to a sophisticated laboratory is not required, these devices have great promise for use in remote locations. The main advantage of on-site analysis, however, is the potential for rapid assessment and response to problem situations in the workplace. In air sampling, colorimetric and similar devices can be designed for short-term, near real-time monitoring or for longer term time-integrated measurements. Their mode of sampling can be further classified as either "active" (pumped) or "passive" (diffusive). Depending on the type of sampling, the type of reaction, and the type of measurement, the theory of operation leads to linear or semilinear relationships between the measurement (length or depth of stain, absorbance, or reflectance) and the concentration of the species being measured. However, little credence is given to theoretical relationships without adequate confirmation from performance testing, and rightly so, as there are many possible interferences that may be encountered during sampling and analysis. This article covers the available standards for performance evaluation of these types of equipment. A useful guide to the types of accessible equipment has already been published.(1)
Keywords
Chemical-analysis; Analytical-methods; Chemical-indicators; Chemical-reactions; Colorimeters; Colorimetry; Measurement-equipment; Analytical-instruments; Sampling-equipment; Air-sampling-equipment; Air-sampling-techniques; Exposure-assessment; Air-quality-monitoring; Air-sampling; Air-monitoring; Sampling; Sampling-methods; Standards; Performance-capability; Testing-equipment; Equipment-reliability
