Advancing Tape-Based Colorimetric Detector

Rgure 10.4 Schematic diagiam of tape-based colorimetric detector. 

An electronic device called a colorimeter that measures the color intensity is used to determine the intensity of the color that can be related to concentration. This colorimeter measures the light reflected from the exposed stain as well as the light reflected from an unstained area as the reference. The difference between the two signals is used to determine detection. Alternatively, the rate of color formation or color fading could also be used. The instrument can first measure the color at the time the developer reagent is added as compared to the subsequent color intensity after a time interval. This type of instrument usually includes temperature controls that accelerate the rate of reaction. 

This colorimetric tape method provides much faster detection of low-concentration samples than badges or tubes could provide. Its LOD can be as low as parts per billion. More importantly, this method provides continuous detection capability that tubes or badges lack. It also records exposure history. 

The Domestic Preparedness Program has tested two types of these tubes for CWA detection ability. For example, the thioether tubes can detect HD, and phosphoric acid ester tubes can detect nerve agents at very low concentrations. 

military has also used similar enzyme detection techniques, but does not depend on moving tape for CWA detection, which was known as the real-time monitor in the 1970s. This is another example of how colorimetric detectors can be used in CWA detection. The system was developed for safety monitoring of 

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