Radiant energy – Ionic separation or analysis – Methods
Reexamination Certificate
1999-07-16
2002-09-03
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Ionic separation or analysis
Methods
C250S281000
Reexamination Certificate
active
06444979
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of and an apparatus for, and a recording medium with a recorded computer program for, searching for an unknown specimen, i.e., identifying an unknown polymer such as a plastic or synthetic resin.
2. Description of the Prior Art
It has heretofore been known to identify an unknown polymer by producing data of the unknown polymer according to a process (Py-GC/MS) which is a combination of pyrolysis gas chromatography (Py-GC) and mass spectrometry (MS), and comparing the produced data with a library. Specifically, the data of the unknown polymer are compared with data of known polymers stored in the library to search for the data of the known polymer which agree with the data of the unknown polymer.
According to the Py-GC/MS process, a pyrolytic product of the unknown polymer is separated by a capillary column and analyzed by a mass spectrometer, which detects the intensities of molecular ions and fragment ions that are generated when an electron beam is applied to separated molecules. In the mass spectrometer, each time an electron beam is applied to the separated molecules for a predetermined period of time, e.g., 0.008 minute, one set of ion intensities is obtained as detected data. The detected ion intensities of each set are added to calculate a total ion intensity, and the total ion intensities of the sets are plotted successively at detected times, producing a pyrolysis gas chromatogram (pyrogram) as shown in
FIG. 5
of the accompanying drawings.
The pyrogram itself may be compared with the pyrogram of a known polymer specimen to identify the unknown polymer. According to the Py-GC/MS process, however, it is customary to generate mass spectra of peaks of the pyrogram and search a library of mass spectra of known polymers based on the generated mass spectra.
For example, when the ion intensities of total ion intensities that make up portions corresponding to the maximum points of the peaks, as representative values of the total ion intensities, are arranged in the order of masses of the molecular ions and the fragment ions, there is obtained a mass spectrum having a pattern inherent in compounds corresponding to the peaks. The mass spectrum is compared with a library of mass spectra produced with respect to standard specimens to search for a mass spectrum in the library that agrees with the mass spectrum for thereby identifying the unknown polymer.
The above conventional library searching process will be described below with respect to an example in which a pyrogram shown in
FIG. 5
of the accompanying drawings is plotted as the pyrogram of an unknown polymer. According to the conventional library searching process, the total ion intensity that makes up a portion corresponding to the maximum point of a peak D is divided into individual ion intensities. Then, when the individual ion intensities are arranged in the order of masses of molecular ions and fragment ions, a mass spectrum shown in
FIG. 6
of the accompanying drawings is obtained. The mass spectrum shown in
FIG. 6
is then compared with a library of mass spectra produced with respect to standard specimens to search for the mass spectrum of a known polymer in the library that agrees with a high probability percentage with the mass spectrum for thereby identifying the unknown polymer.
When a commercial library (WILEY) is searched for the mass spectrum shown in
FIG. 6
, a result is obtained as shown in FIGS.
10
(
a
) through
10
(
d
). FIGS.
10
(
a
) and
10
(
b
) show mass spectra of 4,4′-(1-methylethylidene) bisphenol. FIG.
10
(
c
) shows a mass spectrum of p-phenyl-carbanilic acid, and FIG.
10
(
d
) shows a mass spectrum of [1,1′-biphenyl]-3-yl-carbamic acid. The probability that a pyrolytic product corresponding to the mass spectrum shown in
FIG. 6
is the same as the compounds shown in FIGS.
10
(
a
) through
10
(
d
) is 97%, 83%, 46%, and 43%, respectively.
According to the conventional library searching process, each of the peaks of the pyrogram shown in
FIG. 5
is processed in the same manner as with the peak D to identify compounds corresponding to the peaks.
However, the conventional library searching process is time-consuming because the library needs to be searched for each one of the pyrolytic products corresponding to the peaks. Even if each one of the compounds corresponding to the peaks is identified, it requires a high level of expert knowledge, experience, and skill to determine the original polymer from the compounds thus identified.
Another process of searching for an unknown polymer uses a mass spectrum measured by directly pyrolyzing the polymer in a mass spectrometer. According to this process, one mass spectrum is obtained with respect to one polymer. Therefore, it is not necessary to search a library for individual mass spectra corresponding to peaks, and it is possible to determine an original polymer immediately from the search result.
The above process requires that a specimen introduced into the mass spectrometer be in a minute quantity of several &mgr;g or less. However, it is practically difficult to weigh such a minute quantity of specimen. Polymers that are dissolvable into solvents can be weighed in minute quantities of several &mgr;g by adjusting the concentration of the solution. However, such a weighing scheme is not applicable to crosslinked polymers that are not dissolvable into solvents.
Another problem is that when a specimen of several hundred &mgr;g that can be weighed is pyrolyzed, the ionization chamber in the mass spectrometer is contaminated and becomes useless in a short period of time.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and apparatus, along with a recording medium with a recorded computer program, for easily identifying an unknown polymer such as a plastic or synthetic resin.
To achieve the above object, there is provided in accordance with the present invention a method of searching for an unknown polymer, comprising the steps of separating a mixture of pyrolytic products obtained by pyrolyzing an unknown polymer into the pyrolytic products, detecting ion intensities of molecule ions and fragment ions produced by ionizing the separated pyrolytic products in cycles each for a predetermined period of time, adding sets of the ion intensities of the molecule ions and the fragment ions detected in the cycles into total ion intensities, interconnecting maximum levels of the total ion intensities in a histogram composed of the total ion intensities arranged in the order of detection times thereof for thereby plotting a chromatogram, combining, for each ion of the same mass, the ion intensities contained in all the total ion intensities making up peaks in the chromatogram into combined data of the ion intensities of the molecular ions and the fragment ions, generating a combined mass spectrum of the unknown polymer which is composed of the combined data arranged in the order of masses of the molecular ions and the fragment ions, and comparing the generated combined mass spectrum of the unknown polymer with a library of combined mass spectra of a plurality of known polymers which are generated in the same manner as with the combined mass spectrum of the unknown polymer, for thereby searching for the combined mass spectrum of one of the known polymers which agrees with a high probability percentage with the combined mass spectrum of the unknown polymer.
In the above searching method, a mixture of pyrolytic products obtained by pyrolyzing an unknown polymer is separated into the pyrolytic products. The pyrolytic products are ionized, and ion intensities of generated molecule ions and fragment ions are detected. Then, total ion intensities as totals of the ion intensities detected in cycles each for a predetermined period of time are calculated, and arranged in the order of detection times thereof thereby to generate a chromatogram of the unknown polymer.
The peaks in the chromatogram which cor
Arent Fox Kintner & Plotkin & Kahn, PLLC
Frontier Laboratories Ltd.
Nguyen Kiet T.
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