Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2001-01-19
2004-05-04
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S064530, C356S432000, C250S339100
Reexamination Certificate
active
06729185
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to photoacoustic analysis of a sample using a photoacoustic sample vessel. As used herein, the sample is a material that may be a gas, liquid, solid, or combination thereof including supercritical fluid, slurry, and suspension.
BACKGROUND OF THE INVENTION
Photoacoustic or optoacoustic methods are used as a tool in many applications to obtain chemical and physical information on the properties of materials in solution, solids, or gases. Absorption of irradiation, for example electromagnetic, by a material generates an electronically/vibrationally-excited state intermediate. Several channels of excited state “deactivation” lead to an observable photo-induced acoustic signal including (1) heat released from the excited state as it relaxes back to the ground state, (2) volume changes in the material due to absorption of light, and/or (3) electrostriction of the media surrounding the material due to polar changes in the excited state.
All three phenomena of heat, volume, and electrostriction generate an acoustic wave that is typically detected with a piezoelectric transducer. A photoacoustic vessel couples the light into the material and couples the resulting acoustic wave to the transducer.
Referring to
FIG. 1
, a typical photoacoustic vessel
100
comprises an acoustic detector
110
and an acoustic coupler
102
(usually known as a cuvette) that provides a chamber for holding a sample
108
. The acoustic coupler
102
has a first body
104
(vertical sides or walls) and a second body
106
(bottom). The first body
104
cooperates with the second body
106
(by being attached) to form the chamber. The acoustic detector
110
is mounted on the second body
106
. Thus, upon introduction of electromagnetic energy
112
, for example light, an acoustic signal
114
is generated within the sample
108
and propagates through the sample
108
into and through the acoustic coupler
102
to the acoustic detector
110
.
A disadvantage of the cuvette type photoacoustic vessel is a requirement for a relatively large volume (milliliters) of sample
108
required to perform the measurement. Specifically, in the life sciences fields, new biological samples may be extremely expensive or difficult to obtain, synthesize, or purify. Thus, there is a need for photoacoustic vessels having smaller sample volumes for obtaining important data. Another disadvantage of this technique is the limitation of the sample
108
being at atmospheric pressure due to the chamber provided by the cuvette being open to the environment.
FIG. 2
illustrates an improved photoacoustic vessel
100
′ described in U.S. patent application Ser. No. 09/105,781 now U.S. Pat. No. 6,236,455, filed Jun. 26, 1998, incorporated by reference herein to the extent not inconsistent with the disclosure herewith. The photoacoustic vessel
100
′ comprises an acoustic detector
110
and an acoustic coupler
102
′ (referred to as a prism cell) that provides an enclosed chamber for holding a sample
108
. The acoustic coupler
102
′ has a first body
104
and a second body
106
with a shim
200
or spacer therebetween defining the chamber containing the sample
108
. The shim
200
contacts a perimeter of the first and second bodies
104
,
106
as shown thereby forming a perimeter wall(s). The first body
104
forms a first wall of the chamber and the second body
106
forms a second wall of the chamber. The second body
106
has an acoustic detector
110
mounted thereon. Thus, upon introduction of electromagnetic energy (e.g., light)
112
an acoustic signal
114
is generated within the sample
108
and propagates through the sample
108
into and through the second body
106
to the acoustic detector
110
. Sample volumes of less than 1 ml and as low as 0.1 ml have been achieved with this device.
High-pressure time-resolved photoacoustic studies have been done and obtained results for the kinetics of photo-generated meta-stable intermediates ([a] E. F. Walsh, M. W. George, S. Goff, S. M. Nikiforov, V. K. Popov, X.-Z. Sun, and M. Poliakoff, Energetics of the Reactions of (n
6
-C
6
H
6
)Cr(CO)
3
with n-Heptane, N
2
, and H
2
Studied by High-Pressure Photoacoustic Calorimetry,
J. Phys. Chem.,
100 (1996) 19425-19429; [b] E. F. Walsh, V. K. Popov, M. W. George, and M. Poliakoff, Photoacoustic Calorimetry at High Pressure: A New Approach to Determination of Bond Strengths. Estimation of the M—L Bond Dissociation Energy of M(CO)
5
L (M=Cr, Mo; L=H
2
, N
2
) in n-Heptane Solution,
J. Phys. Chem.,
99 (1995) 12016-20). Pressures up to 130 bar (2000 psi) were reported. In addition to the upper pressure limitation, these systems were not conducive to obtaining time-resolved data, limited to optically dense samples, and had no flow-through capability.
Thus, in spite of these advances, there continue to be applications requiring yet smaller sample volumes (e.g., nanoliters). In addition, because photoacoustic methods generally are highly sensitive but have low selectivity, there remains a need for obtaining dynamic photoacoustic data to enhance the selectivity of the opto- or photo-acoustic technique.
BRIEF SUMMARY OF THE INVENTION
The present invention is an improved photoacoustic vessel and method of photoacoustic analysis. The photoacoustic sample vessel comprises an acoustic detector, an acoustic couplant, and an acoustic coupler having a chamber for holding the acoustic couplant and a sample. The acoustic couplant is selected from the group consisting of liquid, solid, and combinations thereof. Passing electromagnetic energy through the sample generates an acoustic signal within the sample, whereby the acoustic signal propagates through the sample to and through the acoustic couplant to the acoustic detector.
In another embodiment of the present invention, the photoacoustic sample vessel further comprises a sample container, wherein the sample is contained within the sample container and the acoustic signal propagates through the sample into and through the wall of the container into and through the acoustic couplant to the acoustic detector.
In another embodiment of the present invention, the sample is pressurized above atmospheric pressure.
It is an object of the present invention to provide a photoacoustic sample vessel that uses a small sample volume.
It is a further object of the present invention to provide a method of photoacoustic analysis of samples at elevated pressure.
It is a further object of the present invention to provide a method of dynamic photoacoustic analysis.
An advantage of the present invention is the ability to use substantially reduced sample volume needed for a photoacoustic measurement. Specifically, the present invention is capable of using a sample volume of less than 0.1 ml and as low as a few nanoliters. An additional advantage is the capability to perform measurements under elevated pressures as great as 60,000 psi. Further, it is possible to obtain time-resolved data (dynamic signal analysis for greater selectivity) with the present invention. Analysis of the shape of the acoustic waveform provides the selectivity while analysis of the amplitude provides the sensitivity.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.
REFERENCES:
patent: 4184768 (1980-01-01), Murphy et al.
patent: 4276780 (1981-07-01), Patel et al.
patent: 4436428 (1984-03-01), Watanabe et al.
patent: 4818882 (1989-04-01), Nexo et al.
patent: 5444541 (1995-08-01), Small et al.
patent: 5596146 (1997-01-01), Waller et al.
patent: 5913234 (1999-06-01), Julliard et al.
patent: 6236455 (2001-05-01), Autrey et al.
patent: 6244101 (2001-06-01), Autrey et al.
patent:
Autrey Tom
Yonker Clement R.
Battelle (Memorial Institute)
Fayyaz Nashmiya
May Stephen R.
McKinley, Jr. Douglas E.
Williams Hezron
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