Patent Description:
Tires for automobiles (pneumatic tires for automobiles) are constituted by parts such as a carcass, an inner liner, a bead wire, and a tread compound, and materials suitable for the functions of the parts are selected as materials of the parts. In particular, the tread compound positioned on the outermost periphery of the tire is involved in running performance of automobiles such as braking performance or rolling resistance of the tire, so that the selection of suitable materials is important in terms of improving the running performance of automobiles.

The material for the tread compound usually contains a polymer, a filler and a softening agent. Among these, the properties of the polymer which accounts for approximately <NUM>% of the whole materials are said to be involved in the running performance of the tire. A styrene-butadiene rubber (SBR) which is a copolymer of styrene with <NUM>,<NUM>-butadiene is excellent in heat resistance, wear resistance, mechanical strength, and other properties, and is therefore widely used as a material for automobile tire tread compounds. The SBR has a characteristic chain structure in which styrene, cis-<NUM>,<NUM>-butadiene, trans-<NUM>,<NUM>-butadiene, and vinyl are linearly linked in a large number, so that a method for properly evaluating the performance of the tread compound by analyzing the SBR chain structure is sought.

Examples of a method for analyzing a structure of an organic compound include infrared spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and chromatography. For analyzing the SBR chain structure, any of these methods disadvantageously provides insufficient information, or conversely, provides excessively complex information, which is time-consuming for analysis. For example, the infrared spectroscopy can conveniently measure amounts of styrene, vinyl, cis-butadiene, and trans-butadiene contained in the SBR, but can acquire only information in monomer units. The NMR spectroscopy can provide information about the structure at an atomic level, but the information is excessively complex, so that analysis of the SBR chain structure is time-consuming. Further, as a technique for separating a pyrolyzate obtained by pyrolyzing the SBR, pyrolysis gas chromatography (GC) may be used. This technique, however, can only provide information about the amount ratio of styrene to butadiene that constitute the SBR.

A glass transition point (Tg) is one of indexes representing performance of rubber. The lower the glass transition point of a rubber is, the more the degradation of the performance is suppressed in a low temperature region, which can provide a tire having excellent cold resistance. Since the glass transition point of an SBR is known to be determined depending on the amounts of styrene and vinyl, there has been proposed a method in which the SBR is decomposed into a chain component composed of a component derived from styrene, a chain component composed of a component derived from vinyl, and a chain component composed of a component derived from styrene and a component derived from vinyl by ozonolysis reaction, and these chain components are analyzed by gel permeation chromatography (GPC) (Non-Patent Literature <NUM>). In this method, however, there is a problem that although the chain component derived from styrene can be separated by the difference in the number of chains, the chain component derived from vinyl has a poor separation ability.

Non-Patent Literature <NUM> describes the analysis of styrene-vinyl sequences in SBR by ozonolysis-LC/MS. The chain components were separated by reverse phase LC. Non-Patent Literature <NUM> describes the characterization of polymers by multidimensional chromatography. Patent Literature <NUM> describes methods and apparatus for characterizing libraries of polymers samples using in a comprehensive, directly-coupled multi-dimensional liquid chromatography system.

The SBR is described herein as an example, but a copolymer of a conjugated diene compound with an aromatic vinyl compound has also a similar problem to the SBR.

An object of the present invention is to analyze all components obtained by ozonolysis of a copolymer of a conjugated diene compound with an aromatic vinyl compound.

The present invention that has been made to solve the above-mentioned problem is a method for analyzing a copolymer, the method including:.

When the copolymer of the conjugated diene compound with the aromatic vinyl compound is subjected to ozonolysis, a carbon-carbon double bond derived from the conjugated diene compound among carbon-carbon double bonds of the copolymer is cleaved to produce an ozonide, and the ozonide is ring-opened by reduction reaction to produce a polyhydric alcohol compound. At this time, polyhydric alcohol compounds with various chain structures can be obtained in which the number or kind of linking monomers varies depending on the structure of the moiety sandwiched between two carbon-carbon double bonds of the copolymer. For example, when a styrene-butadiene copolymer is subjected to ozonolysis, the moiety polymerized at the <NUM>,<NUM>- bond is cleaved. Furthermore, a vinyl group in a side chain is oxidized to be a hydroxymethyl group. As a result, in the styrene-butadiene copolymer, a repeating unit which is sandwiched by adjacent two butadiene units polymerized at the <NUM>,<NUM>-bonds is produced as an ozonolysis component. For example, when the moiety sandwiched between two butadiene units that have been polymerized at the <NUM>,<NUM>-bonds in the main chain is subjected to ozonolysis, a polyhydric alcohol compound with a chain structure composed of styrene units, a polyhydric alcohol compound with a chain structure composed of vinyl units, and a polyhydric alcohol compound with a chain structure composed of styrene units and vinyl units are obtained.

The polyhydric alcohol compounds with a plurality of kinds of chain structures (polyhydric alcohol compounds with chain structures composed of either styrene units or vinyl units, or both) as described above can be separated using LC such as GPC or reversed phase liquid chromatography (hereinafter referred to as "RPLC"). In this case, the polyhydric alcohol compound with a chain structure composed of styrene units alone and the polyhydric alcohol compound with a chain structure composed of both styrene units and vinyl units can be detected with a UV detector such as an ultraviolet visible light spectroscopic detector by utilizing ultraviolet absorption of the styrene unit. The polyhydric alcohol compound with a chain structure composed of vinyl units alone cannot, however, be detected with a UV detector. In contrast to this, the present invention uses a mass spectrometer, so that polyhydric alcohol compounds with various chain structures obtained by subjecting the copolymer of the conjugated diene compound with the aromatic vinyl compound to ozonolysis can be detected. Besides, when the mass-to-charge ratios of a plurality of components contained in the sample vary, the mass spectrometer can distinguish and detect the plurality of components. Therefore, even though the plurality of kinds of polyhydric alcohol compounds contained in the ozonolysis product of the copolymer are insufficiently separated by LC, they can be individually distinguished and then detected.

In the mass spectrometer, any of a scanning mode for detecting ions while voltage applied to an electrode is continuously changed; a selected ion monitoring (SIM) measurement mode for detecting ions having specific mass-to-charge ratios; and a selected reaction monitoring (SRM) measurement mode for selecting precursor ions having specific mass-to-charge ratios and detecting an ion having a specific mass-to-charge ratio among product ions of the precursor ions may be used, and in particular, in the case of performing quantitative analysis of the polyhydric alcohol compound, SIM measurement or SRM measurement is preferable.

As described above, the plurality of kinds of polyhydric alcohol compounds contained in the ozonolysis product of the copolymer can be accurately detected by combining LC such as GPC or RPLC with a mass spectrometer. However, by using a comprehensive two-dimensional liquid chromatograph (sometimes referred to as "LC x LC", and hereinafter referred to as a comprehensive two-dimensional LC) equipped with two-stage columns including a first column and a second column as LC, the polyhydric alcohol compounds with various chain structures can be more accurately separated, so that the plurality of kinds of polyhydric alcohol compounds can be more accurately detected. With the comprehensive two-dimensional LC, various kinds of components in the sample are first separated in the first column and the eluted component is introduced into a modulator. The modulator repeats an operation in which a solvent (including a component to be analyzed) introduced at every predetermined time interval is stored and the stored solvent is then introduced into the second column. Usually, the first and second columns which have different polarities or different separation modes are used, and a column which exhibits separation behavior different from that of the first column is used as the second column. Thus, even though some of the plurality of kinds of polyhydric alcohol compounds obtained by the ozonolysis of the copolymer and the reduction reaction cannot be sufficiently separated because of the very close elution time in the first column, they can be separated in the second column.

In the case of using the comprehensive two-dimensional LC, a two-dimensional chromatogram may be created with the elution time in the first column and the elution time in the second column as axes and with a signal intensity represented in contour, or a three-dimensional chromatogram may be created with the signal intensity also as an axis, based on detection results with the mass spectrometer. From the shape of the two-dimensional chromatogram or the three-dimensional chromatogram, the chain structure contained in the copolymer can be recognized, which facilitates analysis of the structure or characteristics of the copolymer.

According to the present invention, a sample solution containing polyhydric alcohol compounds with various chain structures obtained by subjecting as an analyte a copolymer of a conjugated diene compound with an aromatic vinyl compound to ozonolysis can be separated into a polyhydric alcohol compound with a chain structure composed of styrene units, a polyhydric alcohol compound with a chain structure composed of vinyl units, and a polyhydric alcohol compound with a chain structure composed of styrene units and vinyl units by LC, and the separated products can be analyzed with a mass spectrometer. Therefore, all the polyhydric alcohol compounds with various chain structures contained in the sample solution can be analyzed.

Similarly, according to the method for quantitatively analyzing a polyhydric alcohol compound of the present invention, polyhydric alcohol compounds with various chain structures obtained by subjecting as an analyte a copolymer of a conjugated diene compound with an aromatic vinyl compound to ozonolysis can be separated based on a difference in the chain structure, and the separated products can be analyzed. Therefore, the properties of the copolymer can be evaluated from the analysis results.

A method for analyzing a copolymer, a method for quantitatively analyzing a polyhydric alcohol compound, and a method for separating an ozonolysis product of SBR will be described hereinafter in detail.

A copolymer of a conjugated diene compound with an aromatic vinyl compound, which is an analyte of the present invention, has a structure in which a structure derived from the conjugated diene compound, a structure derived from the aromatic vinyl, and a structure derived from vinyl are linearly linked, and has a carbon-carbon double bond derived from the conjugated diene compound and the vinyl group. As an example of the copolymer, a styrene-butadiene rubber (hereinafter referred to as SBR), which is a copolymer of <NUM>,<NUM>-butadiene with styrene, may be used. The SBR has a chain structure in which a styrene-derived component; cis-<NUM>,<NUM>-butadiene and trans-<NUM>,<NUM>-butadiene which are <NUM>,<NUM>-butadiene-derived components; and a vinyl group are linearly linked in a large number (see <FIG>).

In the analysis method of the present invention, first, the copolymer of the conjugated diene compound with the aromatic vinyl compound is subjected to ozonolysis, to thereby produce a polyhydric alcohol compound. The ozonolysis method is performed according to the method described in Non-Patent Literatures <NUM> and <NUM>. According to this method, ozone selectively reacts with a carbon-carbon double bond derived from the conjugated diene compound among the carbon-carbon double bonds contained in the copolymer, so that an ozonide is produced, and the ozonide is then ring-opened by reduction reaction to produce a polyhydric alcohol compound. When the analyte is the SBR, carbon-carbon double bonds derived from butadiene (carbon-carbon double bonds contained in cis-<NUM>,<NUM>-butadiene and trans-<NUM>,<NUM>-butadiene) are ring-opened by ozonolysis, so that a polyhydric alcohol compound with a chain structure composed of styrene units, a polyhydric alcohol compound with a chain structure composed of vinyl units, and a polyhydric alcohol compound with a chain structure composed of styrene units and vinyl units are obtained. For example, when the SBR has a chain structure as shown in <FIG>, a polyhydric alcohol compound shown in <FIG> is obtained by the ozonolysis. In <FIG>, the symbols S, C, T, and V represent structural units of styrene, cis-<NUM>,<NUM>-butadiene, trans-<NUM>,<NUM>-butadiene, and vinyl(<NUM>,<NUM>-butadiene), respectively, and the symbol Va represents a structural unit of allyl alcohol derived from vinyl (<NUM>,<NUM>-butadiene) (see <FIG>) after the ozonolysis.

The polyhydric alcohol compounds obtained by ozonolysis reaction are dissolved in a suitable solvent to produce a sample solution, and the sample solution is then introduced into an LC. As the LC, either an LC having one column or an LC having two columns (first column and second column) may be used. In the case of a comprehensive two-dimensional LC having a first column and a second column, separation may be performed in GPC mode in the first column and in reversed phase LC mode in the second column. When the comprehensive two-dimensional LC in which separation is performed in GPC mode in the first column is used, the ozonolysis product of the SBR is analyzed using a gel permeation chromatography, and the past findings from the results of the analysis are applicable.

The comprehensive two-dimensional LC includes a modulator, as well as the first column and the second column. The sample solution introduced in the comprehensive two-dimensional LC is first separated in the first column and the eluted component is introduced into the modulator. The modulator repeats an operation in which the component introduced at every predetermined time interval is stored and the stored component is then introduced into the second column. Usually, the first and second columns are used which have different separation modes. As the first column, a plurality of columns that are connected together can be used. In this case, a plurality of columns containing a stationary phase of the same kind may be connected or a plurality of columns containing a stationary phase of the same kind but having different pore diameters may be connected. Alternatively, a plurality of columns containing different kinds of stationary phases may be connected.

When the analyte is the SBR which is a copolymer of <NUM>,<NUM>-butadiene with styrene, the first column is preferably filled with a filler including styrene-divinylbenzene copolymer, polyvinyl alcohol or silica gel, as a base material, and the second column is preferably filled with a filler including silica gel or polymer chemically bonded with octadecylsilyl group, phenyl group, octyl group, or pentafluorophenyl propyl group, as a base material.

In addition, as a mobile phase, one or two or more polar solvents or nonpolar solvents selected from chloroform, tetrahydrofuran, water, acetonitrile, isopropanol, ethyl acetate, acetone, hexane, methanol, and ethanol may be used. By using the first column, the second column, and the mobile phase described above, the polyhydric alcohol compound obtained by ozonolysis of the SBR and reduction reaction can be sufficiently separated.

The polyhydric alcohol compound separated by LC is subsequently introduced into a detector. A mass spectrometer is used as the detector. In addition to the mass spectrometer, a detector such as an ultraviolet visible light spectroscopic detector or a photodiode array detector may be used. In the mass spectrometer, any of a scanning mode for detecting ions while voltage applied to an electrode is continuously changed; a selected ion monitoring (SIM) measurement mode for detecting ions having specific mass-to-charge ratios; and a selected reaction monitoring (SRM) measurement mode for selecting precursor ions having specific mass-to-charge ratios and detecting an ion having a specific mass-to-charge ratio among product ions of the precursor ions may be used, and in particular, in the case of performing quantitative analysis of the polyhydric alcohol compound, SIM measurement or SRM measurement is preferable.

In the case of separating the sample solution containing the polyhydric alcohol compound obtained by the ozonolysis reaction with the comprehensive two-dimensional LC, a two-dimensional chromatogram with an elution time in the first column and an elution time in the second column as axes and with a signal intensity of the mass spectrometer represented in contour, or a three-dimensional chromatogram with the elution time in the first column, the elution time in the second column, and the signal intensity of the mass spectrometer as axes can be created based on the detection results with the mass spectrometer. Thus, the chain structure contained in the copolymer can be visually recognized, which facilitates the analysis.

Referring to a calibration curve representing a relationship between the concentration of each kind of the polyhydric alcohol compounds and the ion intensity, the concentration of a polyhydric alcohol compound is calculated from the ion intensity with respect to the polyhydric alcohol compounds in the sample solution detected with the mass spectrometer.

In this case, a calibration curve of a polyhydric alcohol compound having a known mass-to-charge ratio and a known concentration can be created by acquiring a mass chromatogram using results of a standard sample solution containing the polyhydric alcohol compound having the known mass-to-charge ratio and the known concentration detected with a mass spectrometer, and then obtaining an ion intensity from a peak area derived from the known polyhydric alcohol compound appearing on the mass chromatogram.

A calibration curve of a polyhydric alcohol compound having an unknown mass-to-charge ratio may be estimated by using calibration curves created for a plurality of polyhydric alcohol compounds with similar chain structures, the plurality of polyhydric alcohol compounds having known mass-to-charge ratios and known concentrations, to calculate a degree of contribution with respect to ion intensities of components contained in the chain structures.

The method for analyzing a copolymer, the method for quantitatively analyzing a polyhydric alcohol compound, and the method for separating an ozonolysis product of SBR is achieved by using a comprehensive two-dimensional LC mass spectrometer (hereinafter referred to as "comprehensive two-dimensional LC/MS") shown in <FIG>. In the comprehensive two-dimensional LC/MS shown in <FIG>, an analysis section <NUM> includes a first column <NUM>, a sample introduction unit <NUM> that introduces a sample solution into the first column <NUM>, a modulator <NUM> that stores a component (compound) eluted from the first column <NUM> at every predetermined time interval, a second column <NUM> that has a different separation characteristic (typically different polarity) from the first column <NUM> and that enables high speed separation, and a mass spectrometer <NUM> that detects the components separated at two-stage columns <NUM>, <NUM>. The mass spectrometer <NUM> includes, for example, a quadrupole mass filter as a mass analyzer and selectively performs scanning measurement, SIM measurement, and SRM measurement. In the case of requiring more quantitative information, a mass spectrometer including a quadrupole ion trap as a mass analyzer or a time-of-flight mass spectrometer may be used. Alternatively, a hybrid mass spectrometer combined with plurality of kinds of mass analyzers may be used.

The operation of each unit included in the analysis section <NUM> is controlled by an analysis control unit <NUM>. A data processing section <NUM> has functions of processing data acquired at the mass spectrometer <NUM> and of automatically creating a measurement condition file to be used when the analysis control unit <NUM> performs analysis. More specifically, the data processing section <NUM> includes function blocks such as a data storage unit <NUM>, a peak detection processing unit <NUM>, a chromatogram creation unit <NUM>, a calibration curve creation unit <NUM>, a compound table <NUM>, a calibration curve memory <NUM>, and the like. The functions of these function blocks will be described later. The blocks as described above function when part of the data processing section <NUM> or the analysis control unit <NUM> uses a personal computer as hardware, and dedicated control processing software preinstalled in the personal computer is then executed. In the data processing section <NUM>, an operation unit <NUM> which is a pointing device such as a keyboard or a mouse and a display <NUM> are connected. The comprehensive two-dimensional LC/MS of this present example is the same as a conventional comprehensive two-dimensional LC/MS as hardware, but it can substantially have a different configuration by using the control and processing software that is different from conventional one.

Next, a specific example using an ozonolysis product of SBR as the analyte will be described.

A plurality of kinds of standard samples containing polyhydric alcohol compounds having known mass-to-charge ratios and concentrations were analyzed by comprehensive two-dimensional LC/MS. LCMS-<NUM> (product name) manufactured by Shimadzu Corporation was used for the analysis, and measurement was performed in APCI positive MS mode. Analytical conditions and analysis software are shown in <FIG>. In the analysis, GPC was used for primary separation, and RPLC, for secondary separation.

In the standard configuration (e.g., Nexera-e (product name) manufactured by Shimadzu Corporation) of comprehensive two-dimensional LC, a loop of the modulator introduces all the elution solution from the first column to the second column depending on the flow rate and the modulation time. The capacity of the loop (loop size) is, therefore, selected from <NUM>µL, <NUM>µL, and <NUM>µL. In contrast to this, as the analytical conditions listed in <FIG>, in the case where GPC is used for the primary separation using THF as a mobile phase, the volume of the mobile phase in the primary separation to be introduced for the secondary separation may affect the efficiency of the secondary separation. Then, in this analysis, when a small capacity loop (<NUM>µL) was installed in the modulator to attempt to reduce solvent effects, the volume of the elution solution introduced from the first column to the second column decreased, but the separation in the second column was improved.

A correlation plot (calibration curve) between concentration and ion intensity of the polyhydric alcohol compound contained in each of the standard samples was created based on the detection results with the mass spectrometer. The created correlation plots are shown in <FIG>. In <FIG>, the symbols "S1V1", "V1", "S2", and the like represent the number of vinyl-derived structures and the number of styrene-derived structures in the polyhydric alcohol compound which shows the calibration curve. For example, the symbol "S1V1" indicates that the polyhydric alcohol compound has one vinyl (<NUM>,<NUM>-butadiene)-derived structure and one styrene-derived structure. As apparent from <FIG>, the calibration curve varies depending on the number of styrene-derived structures and the number of vinyl-derived structures contained in the polyhydric alcohol compound.

As the standard sample, a commercially available sample may be used, or a sample may also be used which is obtained by collecting a compound separated from an ozonolysis product of SBR and calculating its purity by NMR or the like.

In the case of an SBR having an unknown structure, quantitative analysis of all the polyhydric alcohol compounds cannot be performed with the calibration curves of the polyhydric alcohol compounds shown in <FIG> alone because various kinds of polyhydric alcohol compounds are obtained by the ozonolysis and the reduction reaction. Therefore, a calibration curve of a polyhydric alcohol compound having an unknown mass-to-charge ratio was estimated from the calibration curves created for the standard samples described above.

Specifically, for a chain component Sn of styrene alone, when the number of chains of styrene increased by one, the change amounts of the inclinations of the calibration curves S1 to S3 were calculated to estimate an inclination of a calibration curve for the chain component Sn (n ≥ <NUM>). For a chain component (Vm) of vinyl-derived allyl alcohol alone, an inclination of a calibration curve was estimated in the same manner as above.

For a chain component (SnVm) of styrene and vinyl-derived allyl alcohol, the degree of contribution of the styrene and the vinyl-derived allyl alcohol with respect to the inclination of the calibration curve was obtained from the change amount of the inclination when the number of chains of styrene was fixed and the number of chains of vinyl-derived allyl alcohol was changed, and the change amount of the inclination when the number of chains of vinyl-derived allyl alcohol was fixed and the number of chains of styrene was changed, and the inclination of the calibration curve of the chain component SnVm was then estimated from the degree of contribution and the number of chains of the styrene and the vinyl-derived allyl alcohol. <FIG> show the inclinations of the calibration curves of the chain components obtained from the actual measurement results and the inclinations of the calibration curves estimated by the above-mentioned method.

Using the calibration curves of the polyhydric alcohol compound obtained by the above-mentioned method, chain structures of four SBRs (SBR-A (styrene/vinyl=<NUM>/<NUM> (mol%)), SBR-B (styrene/vinyl=<NUM>/<NUM> (mol%)), SBR-C (styrene/vinyl=<NUM>/<NUM> (mol%)), and SBR-D (styrene/vinyl=<NUM>/<NUM> (mol%))) having known molar ratios of the styrene component/vinyl component were analyzed. The equipment used for the analysis and the analytical conditions are the same as those used for the creation of calibration curves.

The analysis results are shown in <FIG> is a graph showing the amount of the chain components in the components collected after the ozonolysis treatment of the four kinds of SBRs (SBR-A to SBR-D) with an abscissa representing kinds of chain components and an ordinate representing the amounts, and <FIG> is a table listing the amounts of the representative chain components. As apparent from <FIG>, the components collected after the ozonolysis of SBR-A and SBR-B contain excessively large amounts of S1, while the components collected after the ozonolysis of SBR-C and SBR-D contain not only S1 but S3 (S3, S3Vm), S4 (S4Vm) and the like, and also contain a large amount of chain components with <NUM> or more S. Accordingly, it could be confirmed that even in the case where the amount ratio of styrene is similar to that of vinyl, their chain structures were different.

Next, two kinds of commercially available styrene-butadiene copolymers (sample <NUM>: SBR-E (styrene/vinyl=<NUM>/<NUM> (mol%)), sample <NUM>: SBR-F (styrene/vinyl=<NUM>/<NUM> (mol%))) as samples were subjected to ozonolysis reaction to produce a polyhydric alcohol compound, and the polyhydric alcohol compound thus produced was analyzed by comprehensive two-dimensional LC/MS. The equipment used for the analysis and the analytical conditions are the same as those used for creation of the calibration curve.

The detection results with the mass spectrometer was analyzed using the analysis software Chrom Square shown in the table in <FIG>, and a two-dimensional chromatogram with an abscissa representing the elution time in the first column, an ordinate representing the elution time in the second column, and a contour representing the signal intensity was created. As an example of the two-dimensional chromatogram created for the ozonolysis products of the samples <NUM> and <NUM>, two-dimensional chromatograms of the polyhydric alcohol compound ("S2" component) in which the number of styrenes is <NUM> are shown in <FIG>. Further, the contents of the polyhydric alcohol compounds in the samples <NUM> and <NUM> calculated from the two-dimensional chromatogram are shown in <FIG>. Thus, in the present example, it was possible to compare the chain structures of the two samples having different contents of styrene and vinyl.

Although <FIG> show the two-dimensional chromatograms of the "S2" component alone, it is possible to plot the detection results of all the components obtained by the ozonolysis together in a two-dimensional chromatogram. Thus, using the comprehensive two-dimensional LC, even the components that are difficult to be separated in a single analysis of individual dimensions like S1V1 and S1V2 can be separated, so that the difference in the chain structures contained in the copolymer can be visually recognized by displaying the detection results in the two-dimensional chromatogram.

Claim 1:
A method for analyzing a copolymer, the method comprising:
a) subjecting a copolymer of a conjugated diene compound with an aromatic vinyl compound to ozonolysis to produce a plurality of kinds of polyhydric alcohol compounds;
b) separating a sample solution containing the plurality of kinds of polyhydric alcohol compounds with a comprehensive two-dimensional liquid chromatograph equipped with a first column (<NUM>) and a second column (<NUM>); and
c) detecting the separated sample with a detector,
wherein:
the detector is a mass spectrometer (<NUM>); and
the first column (<NUM>) and the second column (<NUM>) have different polarities or different separation modes; and wherein the method comprises:
referring to a calibration curve representing a relationship between a concentration of each kind of the polyhydric alcohol compounds and an ion intensity of the detector; and
calculating a concentration of a polyhydric alcohol compound from the ion intensity with respect to the polyhydric alcohol compounds in the sample solution detected with the detector.