Measuring and testing – Gas analysis – By vibration
Reexamination Certificate
1999-08-31
2001-03-20
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Gas analysis
By vibration
C073S024010, C073S024060, C073S031010, C250S339130, C250S340000, C356S437000
Reexamination Certificate
active
06202470
ABSTRACT:
BACKGROUND
This invention relates to systems and methods for isotope ratio analysis and gas detection, and more particularly to systems and methods for isotope ratio analysis and gas detection using photoacoustics.
In the medical field, it has been known to use radioactive isotope labeled compounds to study various conditions. However, the use of radioactive isotopes creates a problem not only from a storage and disposal standpoint, but also from the standpoint that the dosage provided to the patient must be monitored to avoid excessive radiation, illness or other discomfort.
To depart from the drawbacks associated with the use radioactive isotopes, it has been known that a variety of medical conditions can be examined using stable, non-radioactive isotopes. As described in Lee, U.S. Pat. No. 4,684,805, the metabolism of fat can be examined by monitoring the subject's breath after administration of a stable, non-radioactive isotope-labeled fat. Specifically,
13
C-labeled fat can be administered to the subject, the fat being metabolized and the isotope eliminated from the subject as
13
CO
2
during exhalation. The presence and/or concentration of the
13
CO
2
or the ratio of its concentration to naturally occurring
12
CO
2
can be used to analyze the metabolism and its rate under study.
Similarly, ileal and liver disfunction can be examined by monitoring exhaled breath following injections of
13
C-labeled bile acid and galactose and examining the exhaled breath for the
13
C isotope present as
13
CO
2
. Small intestine bacterial overgrowth can be examined by monitoring exhaled breath for the labeling isotope again occurring as
13
CO
2
following intake of
13
C labeled xylose.
Marshall, U.S. Pat. No. 4,830,010, discloses the use of isotope-labeled urea for diagnosis of gastrointestinal disorders.
As can be appreciated, where applicable, the use of a stable, non-radioactive isotope has vast advantages over the use of a radioactive isotope not only from the storage and disposal standpoint associated with the use of radioactive isotopes but also from a health standpoint.
The shift from use of radioactive isotopes to stable, non-radioactive isotopes in medical analysis only has significant utility if there are satisfactory means and techniques to detect the presence of a labeling isotope. Mass spectrometry is often used for chemical analysis of stable isotopes. A drawback with this technique, however, is that it requires a very high quality vacuum, elaborate sample preparation to remove low levels of water vapor and/or is relatively expensive from an equipment and technician labor standpoint. Furthermore, the mass spectrometric method cannot readily differentiate between compounds with the same mass: for example,
13
CO
2
from
12
COOH and
12
C
16
O
17
O.
Accordingly, if the use of stable, non-radioactive isotopes to study, for example, metabolic rate in a patient are to gain popularity and replace some tests heretofore requiring radioactive isotopes, there is a fundamental need for methods and devices to detect the presence of the labeling, stable, non-radioactive isotope which overcomes the problems associated with the analysis techniques identified above.
In addition to the medical field, isotopic study can also be useful in the geological field. Analysis of the ratio of
13
CO
2
to
12
CO
2
in sedimentation of carbonates or in the atmosphere is important to determine the cycle of CO
2
production and absorption. In Crandall, U.S. Pat. No. 4,517,461, geochemical oil exploration and prospecting by measurement of isotopic compositions of large numbers of individual organic compounds of oil samples is described, to be used to predict locations of other oil reserves or where the oil may have migrated from a common source or formation. In this system, there is a need for a detector to detect the presence of the isotope compounds or constituents of interest, which does not suffer from the problems and drawbacks of the analysis techniques such as mass spectroscopy described above.
Still further and as a departure from isotopic analysis, there is a general need for a detector to detect the presence of certain other suspected constituents in a sample. As but several examples, air samples can be monitored and analyzed for toxic vapors such as CO, NH
3
, HCl, H
2
S, and HF in or about a chemical plant or a power plant or the like. Fast, reliable, and economic detectors directed to the presence of such constituents would constitute a valuable tool to combat pollution and to detect the escape, discharge or presence of harmful compounds. Many current chemical analysis techniques are often unsatisfactory in that they are slow and expensive.
On-Road vehicle emission inspections for pollutants is also important to intercept major pollution offenders and to improve overall air quality. Again, a fast, reliable and accurate method of detection and detector would be a valuable tool to combat air pollution.
As but other examples where a detector and method which is fast, economical, and reliable would be important would be in sampling air proximate a natural gas pipeline to determine the presence of leaks. Soil samples which may contain certain dense nonaqueous phase layer chemicals (DNALP) such as chlorobenzene and others as a pollutant are also in need of a detection method, system and detector which is fast, economical, and reliable to detect the presence of such pollutants.
As another example, in military or security fields, a fast, reliable, and accurate detector and method is needed to determine the presence of explosives or chemical warfare compounds. The
The foregoing are but several examples where there is a need for a reliable, inexpensive detector which does not suffer from the drawbacks of mass spectrometry or gas chromatography.
SUMMARY OF THE INVENTION
There is set forth according to the present invention a photoacoustic system and method for detecting a selected constituent in a gas, the constituent having at least one absorption wavelength in the range of approximately 1700 to 2500 nm. There is also set forth a system and method for examining a metabolic condition of an organism through the introduction of a stable isotope compound to the organism, the isotope liberated from the organism as a sample containing constituent molecules including the isotope having at least one absorption wavelength of between 1700 and 2500 nm, and photoacoustically analyzing the liberated sample from the organism to detect the subject isotope containing constituent. Determining the presence and concentration of the constituent can then be used to determine how the isotope containing compound is metabolized by the organism.
Still further, there is set forth a system and method for using photoacoustic detection of a constituent contained in a non-gaseous sample, the constituent having an absorption wavelength of between approximately 1700 and 2500 nm.
Toward this end, there is set forth a photoacoustic system and method for detecting a selected constituent in a gas, the constituent having at least one telltale or fingerprint absorption wavelength in the range of about 1700 to 2500 nm. The system and method include a source of electromagnetic radiation tunable to selected wavelengths between 1700 to 2500 nm to correspond to the one or more fingerprint wavelengths of the suspected constituent. The radiation is directed into the sample to be absorbed by the constituent. Absorption of the electromagnetic radiation of wavelengths corresponding to the absorption wavelength excites the constituent molecules causing them to collide with surrounding molecules to generate detectable acoustical emissions. For this purpose, the electromagnetic source has sufficient energy to generate acoustical emissions in the sample in response to absorption. It has been found that a pulsed Co:MgF
2
laser having an energy output of approximately 1 to 160 mJ per pulse induces relatively strong acoustic emissions for detection and measurement. A detector such as a microphone is used to detect the acoustic emissions an
Larkin Daniel S.
TRW Inc.
Yatsko Michael S.
LandOfFree
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