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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.
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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:
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Fast: each of the proprietary detector tapes
reacts instantly to the target gas,
providing a visible color reaction.
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Sensitive: tape detectors provide a method
of detecting and analyzing toxic gases that must be identified in
process streams at PPB levels and removed.
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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
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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. |
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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.
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