Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1999-05-03
2001-08-14
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S345000, C250S343000
Reexamination Certificate
active
06274870
ABSTRACT:
TECHNICAL FIELD
The present invention relates to methods and apparatuses for spectrometrically measuring the concentration of an isotopic gas on the basis of a difference in the light absorption characteristics of the isotope.
BACKGROUND ART
Isotopic analyses are useful for diagnosis of a disease in a medical application, in which metabolic functions of a living body can be determined by measuring a change in the concentration or concentration ratio of an isotope after administration of a drug containing the isotope. In the other fields, the isotopic analyses are used for studies of the photosynthesis and metabolism of plants, and for ecological tracing in a geochemical application.
It is generally known that gastric ulcer and gastritis are caused by bacteria called helicobacter pylori (HP) as well as by a stress. If the HP is present in the stomach of a patient, an antibiotic or the like should be administered to the patient for bacteria removal treatment. Therefore, it is indispensable to check if the patient has the HP. The HP has a strong urease activity for decomposing urea into carbon dioxide and ammonia.
Carbon has isotopes having mass numbers of 12, 13 and 14, among which
13
C having a mass number of 13 is easy to handle because of its non-radioactivity and stability.
If the concentration of
13
CO
2
(a final metabolic product) or the concentration ratio of
13
CO
2
to
12
CO
2
in breath of a patient is successfully measured after urea labeled with the isotope
13
C is administered to the patient, the presence of the HP can be confirmed.
However, the concentration ratio of
13
CO
2
to
12
CO
2
in naturally occurring carbon dioxide is 1:100. Therefore, it is difficult to determine the concentration ratio in the breath of the patient with high accuracy.
There have been known methods for determining the concentration ratio of
13
CO
2
to
12
CO
2
by means of infrared spectroscopy (see JPB 61(1986)-42219 and JPB 61(1986)-42220).
In the method disclosed in JPB 61(1986)-42220, two cells respectively having a long path and a short path are provided, the path lengths of which are adjusted such that the light absorption by
13
CO
2
in one cell is equal to the light absorption by
12
CO
2
in the other cell. Light beams transmitted through the two cells are lead to spectrometric means, in which the light intensities are measured at wavelengths each providing the maximum sensitivity. In accordance with this method, the light absorption ratio can be adjusted to “1” for the concentration ratio of
13
CO
2
to
12
CO
2
in naturally occurring carbon dioxide. If the concentration ratio is changed, the light absorption ratio also changes by the amount of a change in the concentration ratio. Thus, the change in the concentration ratio can be determined by measuring a change in the light absorption ratio.
(A) However, the method for determining the concentration ratio according to the aforesaid document suffers from the following drawbacks.
Calibration curves for determining the concentrations of
12
CO
2
should be prepared by using gaseous samples each having a known
12
CO
2
concentration.
To prepare the calibration curve for the
12
CO
2
concentration, the
12
CO
2
absorbances are measured for different
12
CO
2
concentrations. The
12
CO
2
concentrations and the
12
CO
2
absorbances are plotted as abscissa and ordinate, respectively, and the calibration curve is determined by the method of least squares.
The calibration curve for the
13
CO
2
concentration is prepared in the same manner as described above.
For determination of the concentrations by means of infrared spectroscopy, the preparation of the calibration curves is based on an assumption that the relation between the concentration and the absorbance conforms to the Lambert-Beer Law. However, the Lambert-Beer Law itself is an approximate expression. The actual relation between the concentration and the absorbance does not always conform to the Lambert-Beer Law. Therefore, all the plotted data do not perfectly fit to the calibration curve.
FIG. 1
is a graphical representation in which concentration ratios of
13
CO
2
to
12
CO
2
are plotted with respect to
12
CO
2
concentrations, the
12
CO
2
concentrations and the
13
CO
2
concentrations having been determined by using calibration curves prepared on the basis of measurements of the absorbances of gaseous samples having the same concentration ratio (
13
CO
2
concentration/
12
CO
2
concentration=1.077%) but different
12
CO
2
concentrations.
As shown in
FIG. 1
, the concentration ratios determined for different
12
CO
2
concentrations deviate from the actual concentration ratio (1.077%), and form an undulatory curve when plotted.
Although the cause of the deviation has not been elucidated yet, the deviation supposedly results from changes in the spectroscopic characteristics such as reflectance, refractive index and stray light in dependence on the
12
CO
2
concentration and from the error characteristics of the least square method employed for the preparation of the calibration curves.
If the concentration of a component gas is determined without correction of the characteristics associated with the deviation, a critical error may result.
(B) A variety of experiments have revealed that, where the infrared spectrometry is employed to measure the concentration of
13
CO
2
or the concentration ratio of
13
CO
2
to
12
CO
2
(hereinafter referred to as “
13
CO
2
concentration ratio”), measurement results differ from the actual
13
CO
2
concentration or
13
CO
2
concentration ratio depending on the concentration of oxygen contained in a gaseous sample.
FIG. 2
is a graphical representation in which
13
CO
2
concentration ratios are plotted with respect to oxygen contents, the
13
CO
2
concentration ratios having been determined by measuring gaseous samples containing
13
CO
2
diluted with oxygen and nitrogen and having the same
13
CO
2
concentration but different oxygen concentrations. The determined
13
CO
2
concentration ratios are normalized on the basis of a
13
CO
2
concentration ratio for an oxygen content of 0%.
As shown in
FIG. 2
, the
13
CO
2
concentration ratio is not constant but varies depending on the oxygen concentration.
If the
13
CO
2
concentration or the
13
CO
2
concentration ratio of a gaseous sample containing oxygen is measured in ignorance of this fact, it is obvious that a measurement differs from an actual value.
FIG. 3
is a graphical representation illustrating the result of measurement in which gaseous samples having different
13
CO
2
concentration ratios and containing no oxygen were measured. In
FIG. 3
, the actual
13
CO
2
concentration ratios and the measured
13
CO
2
concentration ratios are plotted as abscissa and ordinate, respectively. The
13
CO
2
concentration ratios are normalized on the basis of the minimum
13
CO
2
concentration ratio.
FIG. 4
is a graphical representation illustrating the result of measurement in which gaseous samples having different
13
CO
2
concentration ratios and containing various concentration of oxygen (up to 90%) were measured. In
FIG. 4
, the actual
13
CO
2
concentration ratios and the measured
13
CO
2
concentration ratios are plotted as abscissa and ordinate, respectively. The
13
CO
2
concentration ratios are normalized on the basis of the minimum
13
CO
2
concentration ratio.
A comparison between the results shown in
FIGS. 3 and 4
indicates that the relationship between the actual
13
CO
2
concentration ratio and the measured
13
CO
2
concentration ratio in
FIG. 3
is about 1:1 (or the scope of the fitting curve in
FIG. 3
is about 1) while the relationship between the actual
13
CO
2
concentration ratio and the measured
13
CO
2
concentration ratio in
FIG. 4
is about 1:0.3 (or the scope of the linear fitting curve in
FIG. 4
is about 0.3).
Thus, the measurement of the
13
CO
2
concentration or the
13
CO
2
concentration ratio is influenced by the concentration of oxygen contained in a gaseous sample, the cause of which has not
Hamao Tamotsu
Ikegami Eiji
Kubo Yasuhiro
Maruyama Takashi
Mori Masaaki
Finnegan, Farabow, Garrett, & Dunner L.L.P.
Hannaher Constantine
Israel Andrew
Otsuka Pharmaceutical Co.,Ltd.
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