Dry Colorimetric Detection (DCD): Theory of Operation
Classical colorimetry utilizes an impinger to collect gas in a liquid medium. Chemical reagents are then added to the medium to cause it to change color in proportion to the concentration of gas present. The resulting color change is measured by a laboratory spectrophometer and compared to standards.
Sensi-Tape Detectors are also colorimetric based, but are dry reaction substrates which serve as gas collecting and analyzing media. Individually formulated for a specific gas or family of gases, each Sensi-Tape is a nontoxic, proprietary chemical reagent system. When exposed to a target gas, the tape will change color in proportion to the amount of gas: the higher the concentration, the darker the stain will appear. The change in color, or stain, on the Sensi-Tape is read by a photo-optical system in a C.I monitor, then compared to a standard response curve preprogrammed into the system.
Dry Colorimetric Detection is:
- Fast: each of the proprietary detector tapes reacts instantly to the target gas, providing a visible color reaction.
- Sensitive: tape detectors provide a method of detecting and analyzing toxic gases that must be identified in process streams at PPB levels and removed.
- Specific: while the tape detection system is extremely sensitive to its target gas, it is also very specific to that gas. It will not react to other substances (solvents, hydrocarbons, etc.) often found in process streams. Thus, expensive downtime due to false alarms is virtually eliminated.
Analytical technique
During operation, the Sensi-Tape is incremented through a sampling “window” where it is exposed to a metered sample stream. If the target gas is present, a stain proportional to the concentration develops. Simultaneously, a beam of light is reflected off the exposed portion of the tape and the intensity is measured continuously. As the amount of reflected light decreases due to stain development, the reduction is sensed by a photocell detector as an analog signal. This signal is converted to a digital format, matched to the gas response curve stored in the analyzer’s permanent memory, and displayed/ documented as the actual concentration value. All of these functions are microprocessor controlled.
The use of this spectrophotometric technique, in combination with microprocessor control, provides excellent accuracy, repeatability, and detect-ability of low ppb (parts-per-billion) concentrations.
SENSI-TAPE is copyright C.I. Analytics (2003), standing for a family of dry reaction substrates supplied in the form of a cassette tape. Individually formulated for a specific gas or group of gases, each Sensi-Tape is a non-toxic, proprietary chemical reagent system that acts as both a gas collection and analysis media, detecting and measuring nanograms amounts of the target gas. It is the only detection technique that can act as a trap for the target gas and measure PPB levels accurately.
Quality Control & Sensi-Tape
Sulfur Analysis by DCD