Which direct reading instrument uses a color change to indicate concentration due to a chemical reaction?

Which direct reading instrument uses a color change to indicate concentration due to a chemical reaction?

• A. Photoionization Detectors (PIDs)
• B. Colorimetric Tubes
• C. Adsorption Tubes
• D. Filter Cassettes

Answer: (B)

Colorimetric tubes are direct-reading tools that show concentration through a visible chemical reaction. Inside the tube, a reagent reacts with the target gas, producing a color change. The extent to which color appears—often the length of the colored zone or its intensity—is compared to a calibrated scale to estimate the contaminant’s concentration in the air. This provides an immediate, field-read result without sending a sample to the lab. It’s especially useful for quick screening and simple on-site decisions, though accuracy can be influenced by factors like humidity, temperature, and how precisely the color is interpreted. Other instruments in the list measure concentrations in different ways: some rely on electrical signals from ionization or absorption (not color changes), while others collect samples for later laboratory analysis, rather than giving a direct color-based readout.

Colorimetric tubes are direct-reading tools that show concentration through a visible chemical reaction. Inside the tube, a reagent reacts with the target gas, producing a color change. The extent to which color appears—often the length of the colored zone or its intensity—is compared to a calibrated scale to estimate the contaminant’s concentration in the air. This provides an immediate, field-read result without sending a sample to the lab. It’s especially useful for quick screening and simple on-site decisions, though accuracy can be influenced by factors like humidity, temperature, and how precisely the color is interpreted. Other instruments in the list measure concentrations in different ways: some rely on electrical signals from ionization or absorption (not color changes), while others collect samples for later laboratory analysis, rather than giving a direct color-based readout.