Patent Application
20250237629
This application claims priority to Japanese Patent Application No. 2024-006833 filed on Jan. 19, 2024. The disclosure of Japanese Patent Application No. 2024-006833 is hereby incorporated by reference in its entirety.
The present disclosure relates to methods for quantifying sulfur-containing compounds.
Pyrolysis gas chromatography/mass spectrometry (pyrolysis-GC/MS), for example, is a usual technique to quantify sulfur-containing compounds in compositions containing the sulfur-containing compounds. However, the sensitivity of pyrolysis-GC/MS varies daily and therefore comparison of samples measured on different measurement dates requires correction of the peak intensities with a standard material. Dibenzothiophene, which is stable against heat, is usually used as a standard material (see, Abstracts of the 27th National Symposium on Polymer Analysis and Characterization (2022), I-03, “Analysis of Vulcanization Mechanism of Polybutadiene by MALDI-MS and Pyrolysis GC-MS”).
As described above, dibenzothiophene is usually used as a standard material in quantitative analysis of sulfur-containing compounds. When analyzing multiple samples, an automatic sampler is usually used for operational efficiency. Diligent studies of the present inventors revealed that since dibenzothiophene is a sublimable substance, dibenzothiophene set in an automatic sampler volatilizes over time, so that its peak area decreases. Thus, dibenzothiophene is not appropriate as a standard material in the case of using an automatic sampler.
Then, the present inventors examined the use of alkylthiophene, which is stable against heat and is not a sublimable substance, as a standard material in quantitative analysis of sulfur-containing compounds. The present inventors conducted pyrolysis-GC/MS analysis using a solution of alkylthiophene dissolved in an organic solvent. The result revealed a large variation in the peak areas of samples, indicating that the use of alkylthiophene as a standard material in quantitative analysis of sulfur-containing compounds has room for improvement.
The present disclosure aims to solve the above problem and provide a method for quantifying sulfur-containing compounds enabling long-term stable measurement.
The present disclosure relates to a method for quantifying sulfur-containing compounds, including use of an alkylthiophene-containing rubber composition as a standard material.
The method for quantifying sulfur-containing compounds of the present disclosure includes use of an alkylthiophene-containing rubber composition as a standard material. The method enables long-term stable measurement and can compare the amounts of a sulfur-containing compound in a composition containing the sulfur-containing compound measured at different points in time such as different measurement dates.
The present disclosure provides a method for quantifying sulfur-containing compounds, including use of an alkylthiophene-containing rubber composition as a standard material. This method enables long-term stable measurement and can compare the amounts of a sulfur-containing compound in a composition containing the sulfur-containing compound measured at different points in time such as different measurement dates.
The reason for the advantageous effect is not exactly clear, but it is believed to be as follows. For example, in pyrolysis-GC/MS analysis using a rubber composition prepared by kneading alkylthiophene with rubber as a standard material, a variation in the pyrolysis of the standard material (the rubber composition) is small. Therefore, a variation in the peak area decreases, thereby enabling long-term stable measurement. Thus, presumably, the method can compare the amounts of a sulfur-containing compound in a composition containing the sulfur-containing compound measured at different points in time such as different measurement dates.
The rubber composition to be used as a standard material in the present disclosure at least contains alkylthiophene and a rubber component.
The alkylthiophene may be any compound in which at least one alkyl group is bound to thiophene. Examples of the alkylthiophene include a compound represented by the following formula (1):
In the formula (1), the number of carbon atoms of R is preferably 2 or more, more preferably 5 or more, still more preferably 7 or more, further preferably 10 or more, while it is preferably 27 or less, more preferably 25 or less, still more preferably 23 or less, further preferably 20 or less, particularly preferably 16 or less.
Specific examples of R in the formula (1) include chain-like alkyl groups which may be branched, such as a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a t-butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, a undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an eicosanyl group, a heneicosanyl group, a tetracosanyl group, a nonacosanyl group, and a triacontanyl group.
Examples of the optional substituent of the alkyl group include alkoxy groups such as a methoxy group, an ethoxy group, and a butoxy group; alkenyl groups such as a vinyl group, an allyl group, and a butenyl group; aryl groups such as a phenyl group, a naphthyl group, and a biphenyl group; alkyl groups such as a methyl group, an ethyl group, a butyl group, and a t-butyl group; an ether bond, and an ester bond.
In the formula (1), n represents an integer of 1 to 4, preferably 1, 2, or 3, more preferably 1 or 2, still more preferably 1.
In the formula (1) in which n is an integer of 1 to 3, the position of R bound to the thiophene is not limited.
To better achieve the advantageous effect of the present disclosure, the compound represented by the formula (1) is preferably, for example, a compound represented by the following formula (1-1):
To particularly better achieve the advantageous effect of the present disclosure, the compound represented by the formula (1) is particularly preferably a compound represented by the following formula (1-2):
Non-limiting examples of usable rubber components include diene-based rubbers. Examples of diene-based rubbers include isoprene-based rubbers, polybutadiene rubber (BR), styrene-butadiene rubber (SBR), styrene-isoprene-butadiene rubber (SIBR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile-butadiene rubber (NBR). The examples also include butyl-based rubbers and fluororubber. Each of these may be used alone, or two or more of these may be used in combination.
The amount of the alkylthiophene in the rubber composition is not limited. To better achieve the advantageous effect of the present disclosure, the amount of the alkylthiophene per 100 parts by mass of the rubber component in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, still more preferably 1 part by mass or more, further preferably 1.5 parts by mass or more, while it is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, still more preferably 5 parts by mass or less, further preferably 3 parts by mass or less.
The rubber composition may contain components other than the alkylthiophene and the rubber component within the range not impairing the advantageous effect of the present disclosure. Still, the amounts of other components are desirably as small as possible. Specifically, the amount of other components based on 100% by mass of the rubber composition is preferably 18 by mass or less, more preferably 0.5% by mass or less, still more preferably 0.1% by mass or less, further preferably 0.01% by mass or less.
The rubber composition may be produced by a known kneading method, for example, by kneading the above-described components in a rubber kneader such as an open roll mill or a Banbury mixer.
In the present disclosure, the rubber composition is subjected to, for example, pyrolysis-GC/MS analysis as a standard material. The rubber composition (standard material) is preferably finely cut and accurately weighed before the analysis. The use of such a rubber composition as a standard material can reduce the variation in the pyrolysis of the standard material, thereby reducing a variation in the peak area. Thus, presumably, the method enables long-term stable measurement and can compare the amounts of a sulfur-containing compound in a composition containing the sulfur-containing compound measured at different points in time such as different measurement dates. The weight of the cut piece of the standard material (rubber composition) is preferably 1 g or less, more preferably 100 mg or less, still more preferably 10 mg or less, further preferably 1 mg or less, further preferably 500 μg or less, further preferably 300 μg or less. The lower limit is, for example, preferably 1 μg or more, more preferably 10 μg or more.
The cut standard material (rubber composition) may be prepared by any method, for example, by a known method such as cutting or scraping the rubber composition with scissors or a razor.
The cut standard material (rubber composition) may be in any shape.
The method for quantifying sulfur-containing compounds of the present disclosure preferably includes pyrolysis gas chromatography. Such a method can quantify a sulfur-containing compound in a composition containing the sulfur-containing compound. The sulfur-containing compound can be quantified by subjecting a measurement specimen (sample) to pyrolysis gas chromatography to obtain a pyrogram and then determining the quantity from the peak area or peak height in the pyrogram. The quantification of a sulfur-containing compound in a composition containing the sulfur-containing compound by pyrolysis gas chromatography may be performed by a known method.
The term “pyrolysis gas chromatography” refers to a method involving instantly pyrolyzing a measurement specimen (sample), subjecting the pyrolysis product to gas chromatography, and separating the target component based on the difference in retention time in a column.
The pyrolizer used to pyrolyze the measurement specimen may be a device usually usable in the field. The temperature to pyrolyze the measurement specimen (pyrolysis temperature) is usually within a range of 450° C. to 700° C., preferably within a range of 550° C. to 650° C.
The detector to detect the component separated by the gas chromatography is not limited. For example, a mass spectrometer such as a Time-of-Flight (TOF) mass spectrometer or a flame photometric detector (FPD) for sulfur may be used. In particular, the detector is preferably a flame photometric detector for sulfur that can selectively detect sulfur.
Examples of usable Py-Gc system 10 include, but not limited to, pyrolizer “EGA/PY-3030D” available from Frontier Laboratories Ltd, gas chromatograph “7890” available from Agilent, and Time-of-Flight mass spectrometer “Xevo G2-XS” available from Waters Corporation.
The measurement specimen having undergone Py-Gc analysis is put into the pyrolizer 14. The measurement specimen heated and decomposed in the pyrolizer 14 generates gas. The gas contains decomposed products of multiple components derived from organic matter in the measurement specimen.
The gas generated by the measurement specimen is introduced to the separation column 20 with carrier gas supplied from the carrier gas container 12. The separation column 20 separates multiple components in the gas. The components separated by the separation column 20 are sequentially detected by the detector 18. The detector 18 converts the amounts of the detected components to electrical signals and outputs the signals as a pyrogram from the output device 22. The detection time and the signal intensity are on the horizontal axis and vertical axis, respectively, of the pyrogram.
The output pyrogram shows multiple peaks. Each peak corresponds to a component in the gas generated by the measurement specimen. The area or height of the peak correlates with the amount of the component. Preferable examples of the method to calculate the amount of the component include, but not limited to, an internal standard method based on the peak area or peak height. According to the internal standard method, the standard material (rubber composition) and the measurement specimen together are subjected to pyrolysis gas chromatography. The peak area or peak height corresponding to alkylthiophene in the standard material (rubber composition) is standardized by the amount of the analyzed standard material (rubber composition). The standardized peak area or peak height corresponding to alkylthiophene is compared with the peak area or peak height corresponding to the sulfur-containing compound in the gas generated by the measurement specimen, whereby the sulfur-containing compound in the measurement specimen can be quantified.
The sulfur-containing compound to be quantified is not limited. The quantification method of the present disclosure can quantify any sulfur atom-containing compound.
As described above, the method of the present disclosure uses an alkylthiophene-containing rubber composition as a standard material. Thus, the method enables long-term stable measurement and can compare the amounts of a sulfur-containing compound in a composition containing the sulfur-containing compound measured at different points in time such as different measurement dates.
The present disclosure is specifically described with reference to examples, but the present disclosure is not limited to the examples.
The chemicals used in examples and comparative examples are listed below.
An amount of 0.3 g of the 3-hexadecyl thiophene and 150 g of the rubber were kneaded with a roll to prepare a rubber composition.
An amount of 200 μg of the 3-hexadecyl thiophene was put into 1 mL of the organic solvent and stirred to prepare a 3-hexadecyl thiophene solution.
An amount of 0.3 g of N-cyclohexylbenzothiazole-2-sulfenamide (CZ available from Ouchi Shinko Chemical Industrial Co., Ltd.) and 150 g of the rubber (BR150 available from UBE Corporation) were mixed with a roll to prepare a target component.
An amount of 200 μg of the target component prepared in Preparation Example 3 and 200 μg of the rubber composition prepared in Preparation Example 1 were put into the same sample cup and subjected to Py-Gc analysis described below. Table 1 shows the results (peak intensity ratio and quantified value).
Py-Gc analysis was performed under the conditions described below to obtain a pyrogram. Of the pyrolysis products, 3-hexadecyl thiophene, dibenzothiophene, and benzothiazole were detected from the pyrogram and the peak areas thereof were determined.
Py-GC analysis was performed as in Example 1, except that 200 μg of the target component prepared in Preparation Example 3 and 2 μL of the 3-hexadecyl thiophene solution prepared in Preparation Example 2 were put into the same sample cup. Table 1 shows the results (peak intensity ratio and quantified value).
The peak intensity ratios in Table 1 were calculated with the following equation:
Peak intensity ratio=Peak area of benzothiazole/Peak area of 3-hexadecyl thiophene
Then, the quantified values were calculated with the following equation:
Quantified value (wt %)=Amount of 3-hexadecyl thiophene×Peak intensity ratio
Five sample cups each containing about 200 μg of the rubber composition prepared in Preparation Example 1 were prepared. The cups were subjected to Py-Gc analysis as in Example 1 (measurement interval between samples: 50 minutes). As a result, a chromatogram as illustrated in
Ten sample cups each containing 2 μL of the 3-hexadecyl thiophene solution prepared in Preparation Example 2 were prepared. The cups were subjected to Py-Gc analysis as in Example 1 (measurement interval between samples: 50 minutes). The variation coefficient (CV value) of the peak area (peak intensity) of the 3-hexadecyl thiophene was 25%.
The results of Reference Example 1 and Reference Example 2 demonstrate that the variation in the peak area (peak intensity) of 3-hexadecyl thiophene is larger in the 3-hexadecyl thiophene solution prepared in Preparation Example 2 than the variation in the samples of the rubber composition containing 3-hexadecyl thiophene prepared in Preparation Example 1.
An amount of 250 μg of the dibenzothiophene was put into 1 mL of the organic solvent and stirred to prepare a dibenzothiophene solution. Ten sample cups each containing 2 μL of the dibenzothiophene solution were prepared. The cups were set in an autosampler and sequentially subjected to Py-Gc analysis as in Example 1 (measurement interval between samples: 50 minutes) to determine the peak area of dibenzothiophene. As a result, a graph illustrated in
Five sample cups each containing about 200 μg of the rubber composition prepared in Preparation Example 1 were prepared. The cups were set in an automatic sampler and sequentially subjected to Py-Gc analysis as in Example 1 (measurement interval between samples: 50 minutes). Of the peak areas of 3-hexadecyl thiophene, the peak area of the peak (1) in the chromatogram in
Exemplary embodiments of the present disclosure include the following.
Embodiment 1. A method for quantifying sulfur-containing compounds, including use of an alkylthiophene-containing rubber composition as a standard material.
Embodiment 2. The method for quantifying sulfur-containing compounds according to Embodiment 1, including pyrolysis gas chromatography.
Embodiment 3. The method for quantifying sulfur-containing compounds according to Embodiment 1 or 2, including use of a flame photometric detector for sulfur as a detector.
Embodiment 4. The method for quantifying sulfur-containing compounds according to any combination with any one of Embodiments 1 to 3, wherein the alkylthiophene is a compound represented by the formula (1).
Embodiment 5. The method for quantifying sulfur-containing compounds according to any combination with any one of Embodiments 1 to 4, wherein the alkylthiophene is a compound represented by the formula (1-1).
Embodiment 6. The method for quantifying sulfur-containing compounds according to any combination with any one of Embodiments 1 to 5, wherein the alkylthiophene is a compound represented by the formula (1-2).
Embodiment 7. The method for quantifying sulfur-containing compounds according to any combination with any one of Embodiments 1 to 6,
Embodiment 8. The method for quantifying sulfur-containing compounds according to any combination with any one of Embodiments 1 to 7,
Embodiment 9. The method for quantifying sulfur-containing compounds according to any combination with any one of Embodiments 1 to 8,
| Number | Date | Country | Kind |
|---|---|---|---|
| 2024-006833 | Jan 2024 | JP | national |
