Qualitative and quantitative analysis method for alkane organic matters in complex matrix

Abstract

The invention provides a qualitative and quantitative analysis method for alkane organic matters in a complex matrix, which comprises the following steps: optimizing an MRM method based on a GC-QQQ optimizer, detecting a plurality of n-alkane mixed standard solutions with different concentration gradients, selecting a quantitative ion pair and a qualitative ion pair, establishing a linear regression equation based on the quantitative ion flow peak area and the concentration of each compound, and calculating the qualitative and quantitative analysis result of the alkane organic matters in the complex matrix. Taking the linear regression equation as a quantitative standard curvilinear equation of each compound, and counting the standard retention time of each compound; extracting organic matters in a liquid phase and a solid content of a to-be-detected sample into an organic phase, and circularly washing the raw material for multiple times by using an extraction solvent to obtain a to-be-detected organic phase; detecting a to-be-detected organic phase by using the optimized MRM method to obtain an ion flow peak area and retention time of the to-be-detected organic phase; and obtaining the content of each compound in the to-be-detected sample based on the ion flow peak area of the to-be-detected organic phase and the quantitative standard curve equation, and determining the nature of the compounds based on the retention time of the to-be-detected organic phase and the standard retention time.

Description

Technical Field

[0001] The invention belongs to the field of energy chemical industry and analysis technology, and specifically relates to a qualitative and quantitative analysis method for alkane organic matter in a complex matrix Background Art Coal or biomass is liquefied by hydrothermal liquefaction, wet oxidation, supercritical water liquefaction and other methods, and the resulting liquid products include a large amount of alkane organic matter, which can be separated and purified to obtain useful chemical raw materials or renewable energy.

[0002] In the process of human modernization, the amount of plastic and plastic waste generated in landfills and oceans has increased exponentially. Most plastic waste is landfilled, a small part is incinerated, and some eventually enters the ocean. The current global recycling rate shows that only 9% of plastic waste is recycled. Most plastics take hundreds of years to degrade in the environment. When they degrade slowly, they release toxic particles and chemicals into the environment, causing pollution of surface water, groundwater and oceans. This pollution poses a serious threat to our ecosystems, drinking water, food supply and human health.

[0003] The hydrothermal liquefaction method that uses subcritical or supercritical water to convert plastic waste and other biomass raw materials into liquid products has received widespread attention. This method is a thermochemical depolymerization process in a closed reactor. It can process wet raw materials containing organic pollutants without washing and drying. It can be used to convert biomass raw materials such as plastic waste into bio-crude oil. In order to evaluate the degree of liquefaction reaction of the raw materials and the use of the liquid products, it is necessary to analyze the composition and content of the organic matter in its aqueous solution. However, the quantitative analysis method of alkane organic matter in the liquid products obtained by hydrothermal liquefaction of biomass raw materials is still imperfect, and it is impossible to quickly and accurately perform qualitative and quantitative analysis of alkane organic matter in complex matrices. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a method for qualitative and quantitative analysis of alkane organic matter in a complex matrix, so as to solve the technical problem that it is impossible to quickly and accurately perform qualitative and quantitative analysis of alkane organic matter in a complex matrix.

[0005] The present invention is achieved through the following technical solutions: A method for qualitative and quantitative analysis of alkane organic matter in a complex matrix comprises the following steps: The MRM method was optimized based on the GC-QQQ optimizer. The optimized MRM method was used to detect mixed standard solutions of n-alkanes with various concentration gradients. The quantitative ion pairs and qualitative ion pairs were selected. A linear regression equation was established based on the quantitative ion flow peak area and concentration of each compound. The linear regression equation was used as the quantitative standard curve equation of each compound, and the standard retention time of each compound was calculated. The raw material to be tested is subjected to a hydrothermal liquefaction reaction to obtain a sample to be tested, the organic matter in the liquid phase and solid content of the sample to be tested is extracted into an organic phase, and the raw material is washed by an extraction solvent through multiple cycles to obtain an organic phase to be tested; Use the optimized MRM method to detect the organic phase to be tested, and obtain the ion current peak area and retention time of the organic phase to be tested; The content of each compound in the sample to be tested is obtained based on the ion flow peak area of ​​the organic phase to be tested and the quantitative standard curve equation to complete the quantitative analysis, and the compound is qualitatively analyzed based on the retention time of the organic phase to be tested and the standard retention time.

[0006] Further, the process of optimizing the MRM method based on the GC-QQQ optimizer is: Select the precursor ion with higher response and larger mass; The precursor ions are fragmented at different collision energies, and the product ions with higher responses are selected. The ion pair with the highest response is used as the quantitative ion pair, and two pairs of qualitative ion pairs are selected for each compound. Optimize the collision energy to obtain the collision energy with the highest response.

[0007] Furthermore, for each compound, two pairs of ion pairs with responses just lower than the highest response are selected as qualitative ion pairs.

[0008] Furthermore, the normal alkane mixed standard solution includes C10-C25 normal alkanes.

[0009] Furthermore, the plurality of normal alkane mixed standard solutions with different concentration gradients are: The normal alkane mixed standard solution with a concentration of 1000 μg / mL was diluted to 20 μg / mL, 40 μg / mL, 60 μg / mL, 80 μg / mL and 100 μg / mL as normal alkane mixed standard solutions with various concentration gradients.

[0010] Furthermore, the instruments and equipment used in the optimized MRM method are: Agilent 8890-7000D gas chromatograph coupled with triple quadrupole mass spectrometer.

[0011] Furthermore, the detection conditions in the optimized MRM method are: Chromatographic column: Agilent J&W HP-5, 30m; Carrier gas: helium, purity ≥ 99.999%.

[0012] Furthermore, the temperature during the extraction is 75-100° C., the pressure is 1500 psi, the heating time is 5 min, the static time is 5 min, the flushing volume is 60%, the purge time is 100 seconds; and the number of cycles is 3 times.

[0013] Furthermore, the sample to be tested is extracted into an organic phase in a solvent extractor, and the extraction process adopts a Dionex ASE350 rapid solvent extractor-Gilson ASPECXL liquid processing system.

[0014] Furthermore, the extraction solvent used in the solvent extractor is n-hexane, and the volume ratio of n-hexane to the aqueous solution is 1:1.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: The invention provides a qualitative and quantitative analysis method for alkane organic matter in a complex matrix, comprising the following steps: optimizing an MRM method based on a GC-QQQ optimizer, using the optimized MRM method to detect a plurality of normal alkane mixed standard solutions with different concentration gradients, selecting a quantitative ion pair and a qualitative ion pair, establishing a linear regression equation based on the quantitative ion flow peak area of ​​each compound and its concentration, using the linear regression equation as a quantitative standard curve equation for each compound, and calculating the standard retention time of each compound; subjecting a raw material to be tested to a reaction such as hydrothermal liquefaction to obtain a sample to be tested, and separating the liquid phase and the solid content of the sample to be tested from the sample to be tested. The organic compound is extracted into an organic phase, and the raw material is washed with an extraction solvent through multiple cycles to obtain an organic phase to be tested; the organic phase to be tested is detected using an optimized MRM method to obtain the ion flow peak area and retention time of the organic phase to be tested; the content of each compound in the sample to be tested is obtained based on the ion flow peak area of ​​the organic phase to be tested and the quantitative standard curve equation, and the compound is qualitatively analyzed based on the retention time of the organic phase to be tested and the standard retention time; the present application can completely separate the alkane product in the sample to be tested from other compounds with the same or similar retention time in gas chromatography, and obtain more accurate qualitative and quantitative analysis results of the alkane.

[0016] Furthermore, this method first focuses on selecting precursor ions with high response and large mass number, ensuring that more information-rich product ions can be generated in the subsequent fragmentation process. The precursor ions are fragmented at different collision energies, and the ion pairs with the highest response are carefully screened as quantitative benchmarks to ensure the accuracy of quantitative analysis. In order to enhance the reliability of qualitative analysis, two pairs of ion pairs with responses second only to the highest ion pair are additionally selected for each compound as qualitative ion pairs. Combined with their retention times, a dual judgment criterion for qualitative identification of the compounds to be tested is formed.

[0017] Furthermore, the mixed standard solution of normal alkanes used in this method covers a wide range from C10 to C25, which not only covers common alkane types but also reserves enough analysis windows to deal with unknown components in complex matrices.

[0018] Furthermore, this method achieves sensitive detection and accurate quantification of the target at different concentration levels by accurately configuring a variety of mixed standard solutions with different concentration gradients (such as 20μg / mL to 100μg / mL), providing strong technical support for the analysis of alkane organic matter in the fields of environmental science, petrochemicals, food safety, etc.

[0019] Furthermore, this method uses the DionexASE350 rapid solvent extractor combined with the Gilson ASPEC XL liquid handling system to process the samples to be tested, achieving efficient and automated extraction and subsequent processing processes, improving the extraction efficiency, while ensuring the precise control and reproducibility of the extraction process, reducing human errors, and improving data quality, providing reliable technical support for the qualitative and quantitative analysis of alkane organic matter in complex matrices.

[0020] Furthermore, the method uses n-hexane as the extraction solvent of the solvent extractor and maintains a volume ratio of 1:1 with the aqueous solution, which significantly improves the extraction efficiency and selectivity. n-hexane, as a non-polar solvent, can effectively separate and enrich non-polar alkane organic matter in water samples, while avoiding miscibility with polar components in the aqueous solution, ensuring the cleanliness of the extraction process and the purity of the target. The 1:1 volume ratio optimizes the extraction conditions, ensures sufficient contact and effective mass transfer between the solvent and the target, thereby improving the extraction effect and providing high-quality samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a full scan total ion current diagram of a 100 μg / mL standard solution of an embodiment disclosed in the present invention; Figure 2 The total ion current diagram of the MRM analysis method of the 100 μg / mL standard solution of the disclosed embodiment of the present invention; Figure 3 It is a standard curve diagram of quantitative analysis of decane according to the embodiment disclosed in the present invention; Figure 4 The standard curve diagram of quantitative analysis of undecane in the embodiment disclosed in the present invention; Figure 5 The standard curve diagram of quantitative analysis of dodecane in the disclosed embodiment of the present invention; Figure 6 A standard curve diagram of quantitative analysis of tridecane according to an embodiment of the present invention; Figure 7A standard curve diagram of the quantitative analysis of tetradecane according to an embodiment of the present invention; Figure 8 The standard curve diagram of the quantitative analysis of pentadecane of the embodiment disclosed in the present invention; Fig. 9 A full scan total ion current diagram of a sample to be tested according to an embodiment of the present invention; Fig.10 This is a total ion current diagram of the MRM analysis method of the sample to be tested according to the embodiment of the present invention. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0023] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0024] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0025] The present invention provides a method for qualitative and quantitative analysis of alkane organic matter in a complex matrix, comprising the following steps: The MRM method was optimized based on the GC-QQQ optimizer. The optimized MRM method was used to detect mixed standard solutions of n-alkanes with various concentration gradients. The quantitative ion pairs and qualitative ion pairs were selected. A linear regression equation was established based on the quantitative ion flow peak area and concentration of each compound. The linear regression equation was used as the quantitative standard curve equation of each compound, and the standard retention time of each compound was calculated. The raw material to be tested is subjected to a reaction such as hydrothermal liquefaction to obtain a sample to be tested, the organic matter in the liquid phase and solid content of the sample to be tested is extracted into an organic phase, and the raw material is washed by an extraction solvent through multiple cycles to obtain an organic phase to be tested; Use the optimized MRM method to detect the organic phase to be tested, and obtain the ion current peak area and retention time of the organic phase to be tested; The content of each compound in the sample to be tested is obtained based on the ion flow peak area of ​​the organic phase to be tested and the quantitative standard curve equation to complete the quantitative analysis, and the compound is qualitatively analyzed based on the retention time of the organic phase to be tested and the standard retention time.

[0026] Preferably, the process of optimizing the MRM method based on GC-QQQ optimizer is: Select the precursor ion with higher response and larger mass; The precursor ions are fragmented at different collision energies, and the product ions with higher responses are selected. The ion pair with the highest response is used as the quantitative ion pair, and two pairs of qualitative ion pairs are selected for each compound. Optimize the collision energy to obtain the collision energy with the highest response.

[0027] Specifically, for each compound, two additional ion pairs whose responses are just lower than the highest response are selected as qualifier ion pairs.

[0028] Preferably, in this embodiment, the normal alkane mixed standard solution includes C10-C25 normal alkanes; further, the normal alkane mixed standard solutions with multiple different concentration gradients are: The normal alkane mixed standard solution with a concentration of 1000 μg / mL was diluted to 20 μg / mL, 40 μg / mL, 60 μg / mL, 80 μg / mL and 100 μg / mL as normal alkane mixed standard solutions with various concentration gradients.

[0029] Preferably, the instruments and equipment used in the optimized MRM method are: Agilent 8890-7000D gas chromatograph coupled with triple quadrupole mass spectrometer.

[0030] Preferably, the detection conditions in the optimized MRM method are: Chromatographic column: Agilent J&W HP-5, 30m; Carrier gas: helium, purity ≥ 99.999%.

[0031] Preferably, the sample to be tested is extracted into an organic phase in a rapid solvent extractor; further, the extraction solvent used in the rapid solvent extractor is n-hexane, the volume ratio of n-hexane to aqueous solution is 1:1, and the extraction process uses a Dionex ASE350 rapid solvent extractor-Gilson ASPECXL liquid processing system.

[0032] The present invention provides an embodiment: Preparation of instruments, reagents and materials: Agilent 8890-7000D gas chromatograph coupled with triple quadrupole mass spectrometer; DionexASE350 Rapid Solvent Extractor-GilsonASPECXL Liquid Handling System; n-Alkanes mixed standard (C10-C25), 1000 μg / mL, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Hexane, HPLC grade, was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0033] Sample preparation: The plastic raw material is subjected to hydrothermal liquefaction to obtain an aqueous solution to be tested, the organic matter in the liquid phase and solid content of the aqueous solution to be tested is extracted into an organic phase, and the raw material is washed by an extraction solvent through multiple cycles to obtain an organic phase to be tested, and the obtained organic phase is used for detection by a gas chromatography-tandem triple quadrupole mass spectrometer; Extraction solvent: n-hexane, HPLC grade; The extraction temperature was 75-100°C, the pressure was 1500 psi, the heating time was 5 min, the static time was 5 min, the flushing volume was 60%, the purge time was 100 sec, and the number of cycles was 3.

[0034] Table 1 shows the temperature effect of extracting petroleum hydrocarbons from soil in the embodiment of the present disclosure. Increasing the temperature not only increases the extraction recovery rate, but also improves the repeatability of the extraction. When the temperature is 75-100°C, the extraction recovery rate is about 100%, and the relative standard deviation is small; Table 1 Effect of extraction temperature on the recovery rate of petroleum hydrocarbons extracted from soil

[0035] Configuration of standard solution: The normal alkane mixed standard (C10-C25) with a concentration of 1000 μg / mL is accurately diluted into standard solutions of 20 μg / mL, 40 μg / mL, 60 μg / mL, 80 μg / mL, and 100 μg / mL. The standard solutions are prepared and used immediately, and are usually sealed and stored at -20°C. Determine instrument analysis conditions, including chromatographic conditions and mass spectrometry conditions: Chromatographic column: Agilent J&W HP-5, 30m; Column box heating program: 50℃ for 1 min, then increase the temperature to 260℃ at 3℃ / min, and maintain for 0 min; then increase the temperature to 300℃ at 5℃ / min, and maintain for 0 min; then run backflush for 2 min; Carrier gas: helium, purity ≥99.999%; injection port temperature: 280℃; injection volume: 1μL; injection mode: splitless injection; electron bombardment source: 70eV; ion source temperature: 280℃; transfer line temperature: 280℃; solvent delay: 6min; The full scan total ion current of the 100 μg / mL standard solution obtained under the analytical conditions is as follows: Figure 2 shown.

[0036] Table 2 Organic substances detected in standard solutions and their retention times

[0037] The MRM method was optimized using the GC-QQQ optimizer: first, the precursor ions with higher response and larger mass number were selected; then, the precursor ions were fragmented at different collision energies (5, 15, 25, 35) to select the product ions with higher response. The ion pairs with the highest response were used as the quantitative ion pairs, and two pairs of qualitative ion pairs were selected for each compound; finally, the collision energy was optimized to obtain the collision energy with the highest response, thus obtaining a complete MRM analysis method.

[0038] The total ion current of the 100 μg / mL standard solution obtained according to the optimized MRM analysis method is shown in the figure below: Figure 2 shown.

[0039] Table 3 Ion pairs and collision energy results selected for the optimized MRM analysis method

[0040] Establishment of quantitative method: The prepared standard solutions of 20μg / mL, 40μg / mL, 60μg / mL, 80μg / mL, and 100μg / mL were detected using the optimized MRM method to obtain the linear regression equation of the characteristic ion current peak area y of each compound and its concentration x (μg / mL), and the standard curve equation and its linear correlation coefficient R were obtained. 2 ; The obtained standard curve of C10-C15 alkanes is as follows Figure 3-8 The linear regression equations of the compounds are shown in Table 4: Table 4 Linear regression equation results of each compound

[0041] Testing of actual samples: In this embodiment, the sample to be tested is obtained by hydrothermal liquefaction reaction of plastic raw materials. After sample pretreatment, the optimized MRM method is used for detection, and the characteristic peaks corresponding to the detection compounds are obtained through quantitative and qualitative ion pairs; The total ion current of the full scan of the sample to be tested is as follows: Fig. 9 As shown, the total ion current measured by the MRM analysis method is as follows Fig.10 shown.

[0042] The test results are then used in the quantitative standard curve equation, and the content of each specific compound in the sample to be tested is obtained based on the characteristic ion current peak area of ​​each compound and the quantitative standard curve equation.

[0043] Table 5 Detection results of each compound in the sample to be tested

[0044] Table 6 Qualitative results of compounds detected in the samples to be tested

[0045] The retention time of the detected compounds in the sample to be tested is very close to the retention time of the corresponding compounds in the standard solution, and the accuracy of the two pairs of qualifier ions is about 100%, indicating that the qualitative results of the detected compounds are accurate and reliable.

[0046] The MRM (Multiple Reaction Monitoring) method in the present invention is a mass spectrometry technique, which is mainly used for qualitative and quantitative analysis of target compounds. This technique achieves high sensitivity and high selectivity detection of specific compounds by selectively monitoring the conversion of pre-set parent ions to daughter ions. In the analysis of complex samples, the MRM method is particularly effective because it can filter out interfering signals and focus on the signal measurement of the molecules to be tested, making the quantitative analysis more accurate.

[0047] Finally, it should be noted that the above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved.

[0048] In addition, it should be understood that although this specification is described in accordance with the implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art. The above content is only to illustrate the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for qualitative and quantitative analysis of alkane organic matter in a complex matrix, characterized in that: The following steps are involved: The MRM method was optimized based on the GC-QQQ optimizer. The optimized MRM method was used to detect mixed standard solutions of n-alkanes with various concentration gradients. The quantitative ion pairs and qualitative ion pairs were selected. A linear regression equation was established based on the quantitative ion flow peak area and concentration of each compound. The linear regression equation was used as the quantitative standard curve equation of each compound, and the standard retention time of each compound was calculated. The raw material to be tested is subjected to a hydrothermal liquefaction reaction to obtain a sample to be tested, the organic matter in the liquid phase and solid content of the sample to be tested is extracted into an organic phase, and the raw material is washed by an extraction solvent through multiple cycles to obtain an organic phase to be tested; Use the optimized MRM method to detect the organic phase to be tested, and obtain the ion current peak area and retention time of the organic phase to be tested; The content of each compound in the sample to be tested is obtained based on the ion flow peak area of ​​the organic phase to be tested and the quantitative standard curve equation to complete the quantitative analysis, and the compound is qualitatively analyzed based on the retention time of the organic phase to be tested and the standard retention time.

2. The method for qualitative and quantitative analysis of alkane organic matter in a complex matrix according to claim 1, characterized in that: The process of optimizing the MRM method based on the GC-QQQ optimizer is: Select the precursor ion with higher response and larger mass; The precursor ions are fragmented at different collision energies, and the product ions with higher responses are selected. The ion pair with the highest response is used as the quantitative ion pair, and two pairs of qualitative ion pairs are selected for each compound. Optimize the collision energy to obtain the collision energy with the highest response.

3. The method for qualitative and quantitative analysis of alkane organic matter in a complex matrix according to claim 2, characterized in that: For each compound, two ion pairs with responses just lower than the highest response were selected as qualifier ion pairs.

4. The method for qualitative and quantitative analysis of alkane organic matter in a complex matrix according to claim 1, characterized in that: The normal alkane mixed standard solution includes C10-C25 normal alkanes.

5. The method for qualitative and quantitative analysis of alkane organic matter in a complex matrix according to claim 1, characterized in that: The mixed standard solutions of a plurality of normal alkanes with different concentration gradients are: The normal alkane mixed standard solution with a concentration of 1000 μg / mL was diluted to 20 μg / mL, 40 μg / mL, 60 μg / mL, 80 μg / mL and 100 μg / mL as normal alkane mixed standard solutions with various concentration gradients.

6. The method for qualitative and quantitative analysis of alkane organic matter in a complex matrix according to claim 1, characterized in that: The instruments and equipment used in the optimized MRM method are: Agilent 8890-7000D gas chromatograph coupled with triple quadrupole mass spectrometer.

7. The method for qualitative and quantitative analysis of alkane organic matter in a complex matrix according to claim 1, characterized in that: The detection conditions in the optimized MRM method are: Chromatographic column: Agilent J&W HP-5, 30m; Carrier gas: helium, purity ≥ 99.999%.

8. The method for qualitative and quantitative analysis of alkane organic matter in a complex matrix according to claim 1, characterized in that: The temperature during the extraction is 75-100° C., the pressure is 1500 psi, the heating time is 5 min, the static time is 5 min, the flushing volume is 60%, the purge time is 100 seconds; and the number of cycles is 3 times.

9. The method for qualitative and quantitative analysis of alkane organic matter in a complex matrix according to claim 1, characterized in that: The sample to be tested is extracted into an organic phase in a solvent extractor, and the extraction process adopts a Dionex ASE350 rapid solvent extractor-Gilson ASPECXL liquid processing system.

10. The method for qualitative and quantitative analysis of alkane organic matter in a complex matrix according to claim 7, characterized in that: The extraction solvent used by the solvent extractor is n-hexane, and the volume ratio of n-hexane to the aqueous solution is 1:1.

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