Method for determining cresol trozole in textile

Abstract

The invention belongs to the technical field of cresol trozole determination, and discloses a method for determining cresol trozole in textiles, which comprises the following steps: S1, dissolving cresol trozole by using chromatographically pure tetrahydrofuran, and fixing the volume in a brown volumetric flask to obtain a standard stock solution; placing the standard stock solution in a brown volumetric flask, and fixing the volume with chromatographically pure methanol to obtain a standard working solution; s2, selecting a textile without cresol trozole, soaking the textile in the standard working solution, and drying to obtain a positive sample; s3, the positive sample is cut into pieces and then placed in a glass extractor, and a to-be-detected solution is obtained through extraction; s4, performing liquid chromatograph analysis on the to-be-detected solution to obtain the content of cresol trozole. The analysis method for determining the content of cresol trozole in the textile by using a high performance liquid chromatograph is established, and the method is simple and convenient to operate, high in analysis efficiency and suitable for detecting the cresol trozole in the textile.

Description

Technical Field

[0001] The invention relates to the technical field of drometrizole determination, in particular to a method for determining drometrizole in textiles. Background Art

[0002] Dromtriazole (molecular formula C 13 H 11 N3O, relative molecular mass 225.3) is a UV absorber that can absorb the ultraviolet part of sunlight and fluorescent light sources and has a sunscreen effect, but its excessive use will affect skin health, such as skin papules, dermatitis and other adverse reactions. The International Eco-Textile Research and Testing Association (Oeko-Tex Standard 100), a world-renowned ecological textile labeling agency for hazardous substances, added drometrizole to the monitored substances for the first time in 2023. Although there is no specific limit value at present, OEKO-TEX will conduct necessary random tests on the monitored substances and determine the specific limit requirements based on the test results.

[0003] With the influence of the ozone hole, ultraviolet rays have increased, and anti-ultraviolet clothing has become more and more popular. The risk probability of using drometrizole instead of benzophenone substances as ultraviolet absorbers in sun-proof clothing is also increasing. At present, my country's detection of ultraviolet absorbers in textile and clothing products is mainly benzophenone substances. The national standard GB / T39109-2020 and relevant scholars have studied some determination methods for benzophenone substances in textiles, but there are no reports on the determination / detection methods of drometrizole in textiles. Summary of the invention

[0004] The present invention aims to provide a method for determining drometrizole in textiles, and utilizes a high performance liquid chromatograph to determine the content of drometrizole in textiles, so as to solve the problems of the background technology.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A method for determining drometrizole in textiles comprises the following steps:

[0007] S1. Preparation of standard solution

[0008] Preparation of standard stock solution: Dissolve drometrizole in chromatographically pure tetrahydrofuran and dilute to volume in a brown volumetric flask to obtain a standard stock solution;

[0009] Preparation of standard working solution: Take different volumes of drometrizole standard stock solution and place them in multiple brown volumetric flasks, and dilute to volume with chromatographic pure methanol to obtain standard working solutions with different mass concentrations;

[0010] S2. Preparation of positive samples

[0011] Select a nylon / polyester blended textile that is tested to be free of drometrizole, soak it in the standard working solution prepared in step S1, and then place it in a constant temperature forced air drying oven for drying, wherein the sample is periodically stirred with a glass rod to make drometrizole evenly attached to the fabric sample, to obtain a positive sample;

[0012] S3. Preparation of test solution

[0013] The positive sample obtained in step S2 is cut into pieces and placed in a glass extractor, and an extraction solvent is added to the glass extractor for extraction; the extract is cooled and filtered with an organic phase filter membrane to obtain a test solution;

[0014] S4. Determination of drometrizole

[0015] The solution to be tested obtained in step S3 is subjected to liquid chromatography analysis to determine the content of drometrizole in the solution to be tested.

[0016] Furthermore, in S1, the mass concentration of drometrizole in the prepared standard stock solution is 800 μg / mL; the mass concentrations of drometrizole in the prepared standard working solutions are 10.0, 20.0, 30.0, 40.0, and 50.0 μg / mL, respectively.

[0017] Further, in S2, the positive sample was dried in a forced air drying oven at a constant temperature of 75°C for 3 h, with a stirring cycle of 15 min / time.

[0018] Furthermore, in S3, the solid-liquid ratio of the positive sample and the extraction solvent in the glass extractor is 1:30-50; the extraction solvent is any one of methanol, n-hexane, acetonitrile, acetone, ethyl acetate, toluene, methyl tert-butyl ether, and tetrahydrofuran; the extraction method is ultrasonic extraction, the extraction temperature is 20-60°C, and the extraction time is 30-60min.

[0019] Furthermore, the solid-liquid ratio is 1:30; the extraction solvent is acetonitrile, the extraction temperature is 40°C; the extraction time is 60 minutes; and the pore size of the organic phase filter membrane is 0.45 μm.

[0020] Further, in S4, a high performance liquid chromatograph-diode array detector LC-DAD is used to perform liquid chromatography analysis, wherein the conditions of the liquid chromatography analysis are:

[0021] Chromatographic column: Eclipse XDB-C18 (150 mm × 4.6 mm × 5 μm);

[0022] Flow rate: 0.8 mL / min;

[0023] Column temperature: 25-40°C;

[0024] Injection volume: 20 μL;

[0025] Mobile phase A: secondary water; Mobile phase B: methanol or acetonitrile;

[0026] Elution program: Gradient elution program: 0-10min, A linearly increased from 5% to 70%, maintained for 4min;

[0027] Diode array detector, detection wavelength is 298~336nm;

[0028] Quantitative method: external standard method.

[0029] Furthermore, the column temperature was 40° C.; the mobile phase B was acetonitrile; and the detection wavelength was 336 nm.

[0030] The beneficial effects of the technical solution are:

[0031] The invention provides a method for determining drometrizole in a textile, and establishes an analytical method for determining the drometrizole content in the textile by using a high performance liquid chromatograph. The method is simple to operate and has high analytical efficiency, and is suitable for detecting drometrizole in the textile. The method is of great significance for improving my country's detection capability in the inspection of this project and protecting the health and safety of consumers. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the liquid chromatogram of drometrizole in the embodiment of the present invention;

[0033] Figure 2 is the ultraviolet absorption spectrum of drometrizole in the embodiment of the present invention;

[0034] Figure 3 It is a curve diagram showing the influence of different organic mobile phase systems on the chromatographic retention time of drometrizole in the embodiments of the present invention;

[0035] Figure 4 This is a graph showing the effect of different inorganic mobile phase systems on the chromatographic retention time of drometrizole in the embodiments of the present invention;

[0036] Figure 5 Graph showing the effect of extraction temperature on the normalized extraction efficiency of drometrizole in positive samples of nylon / polyester blended fabrics in an embodiment of the present invention;

[0037] Figure 6 This is a curve diagram showing the effect of extraction time on the normalized extraction efficiency of drometrizole in positive samples of nylon / polyester blended fabrics in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments:

[0039] A method for determining drometrizole in textiles comprises the following steps:

[0040] S1. Preparation of standard solution

[0041] Preparation of standard stock solution: dissolve drometrizole in chromatographically pure tetrahydrofuran and dilute to volume in a brown volumetric flask to obtain a standard stock solution, in which the mass concentration of drometrizole is 800 μg / mL;

[0042] Preparation of standard working solution: different volumes of drometrizole standard stock solution were placed in multiple brown volumetric flasks, and the volume was fixed with chromatographic pure methanol to obtain standard working solutions with different mass concentrations; the mass concentrations of drometrizole in each solution were 10.0, 20.0, 30.0, 40.0, and 50.0 μg / mL, respectively;

[0043] S2. Preparation of positive samples

[0044] Select a nylon / polyester blended textile that is tested to be free of drometrizole, soak it in the standard working solution prepared in step S1, and then place it in a 75°C constant temperature forced air drying oven for drying for 3 hours, wherein the sample is stirred once every 15 minutes using a glass rod to allow drometrizole to be evenly attached to the fabric sample, thereby obtaining a positive sample;

[0045] S3. Preparation of test solution

[0046] The positive sample obtained in step S2 is cut into pieces and placed in a glass extractor, and an extraction solvent is added to the glass extractor for extraction; the extract is cooled and filtered with a 0.45 μm organic phase filter membrane to obtain a test solution; wherein the solid-liquid ratio of the positive sample and the extraction solvent in the glass extractor is 1:30-50; the extraction solvent is any one of methanol, n-hexane, acetonitrile, acetone, ethyl acetate, toluene, methyl tert-butyl ether, and tetrahydrofuran; the extraction method is ultrasonic extraction, the extraction temperature is 20-60°C, and the extraction time is 30-60 min;

[0047] Furthermore, the solid-liquid ratio is 1:30; the extraction solvent is acetonitrile, the extraction temperature is 40°C; the extraction time is 60 min;

[0048] S4. Determination of drometrizole

[0049] The solution to be tested obtained in step S3 is subjected to liquid chromatography analysis using a high performance liquid chromatograph-diode array detector LC-DAD to determine the content of drometrizole in the solution to be tested; wherein,

[0050] The conditions for liquid chromatography analysis were:

[0051] Chromatographic column: Eclipse XDB-C18 (150 mm × 4.6 mm × 5 μm);

[0052] Flow rate: 0.8 mL / min;

[0053] Column temperature: 25-40°C;

[0054] Injection volume: 20 μL;

[0055] Mobile phase A: secondary water; Mobile phase B: methanol or acetonitrile;

[0056] Elution program: Gradient elution program: 0-10min, A linearly increased from 5% to 70%, maintained for 4min;

[0057] Diode array detector, detection wavelength is 298~336nm;

[0058] Quantitative method: external standard method;

[0059] Furthermore, the column temperature was 40° C.; the mobile phase B was acetonitrile; and the detection wavelength was 336 nm.

[0060] Example:

[0061] 1 Experiment

[0062] 1.1 Instruments and Materials

[0063] Instruments: Liquid chromatograph Agilent 1260 (Agilent Technologies Co., Ltd.); ultrasonic generator JP-040 (Shenzhen Jiemeng Cleaning Equipment Co., Ltd.).

[0064] Standard substances, reagents, and materials: drometrizole (standard substance, 98.4%, Bepure); toluene (chromatographic grade, Thermo Fisher Scientific (China) Co., Ltd.); acetonitrile (chromatographic grade, Thermo Fisher Scientific (China) Co., Ltd.); methanol (chromatographic grade, Sinopharm Chemical Reagent Co., Ltd.); methyl tert-butyl ether (chromatographic grade, Thermo Fisher Scientific (China) Co., Ltd.); acetone (chromatographic grade, Dima Technology); tetrahydrofuran (chromatographic grade, Thermo Fisher Scientific (China) Co., Ltd.); ethyl acetate (chromatographic grade, Thermo Fisher Scientific (China) Co., Ltd.); n-hexane (chromatographic grade, Thermo Fisher Scientific (China) Co., Ltd.); nylon / polyester blended fabric (tested to contain no drometrizole).

[0065] 1.2 Preparation of standard solution

[0066] Preparation of standard stock solution: weigh 0.0400 g of drometrizole, dissolve it in chromatographically pure tetrahydrofuran, and dilute to 50 mL in a brown volumetric flask to make the mass concentration of drometrizole 800 μg / mL;

[0067] Preparation of standard working solution: Pipette 0.125, 0.250, 0.375, 0.500, and 0.625 mL of the above-mentioned drometrizole standard stock solution into a 10 mL brown volumetric flask, dilute to volume with chromatographic grade methanol to obtain standard working solutions with mass concentrations of 10.0, 20.0, 30.0, 40.0, and 50.0 μg / mL of drometrizole.

[0068] 1.3 Preparation of positive samples

[0069] A nylon / polyester blended fabric that was tested to be free of drometrizole was selected to prepare a positive sample. 30 g of the nylon / polyester blended fabric was immersed in 50 mL of a standard working solution with a concentration of 540 μg / mL, and placed in a constant temperature forced air drying oven at 75°C for 3 hours. The sample was stirred with a glass rod every 15 minutes to ensure that drometrizole was evenly attached to the fabric sample.

[0070] 1.4 Liquid chromatography analysis

[0071] Load the sample to be tested into the sample injector and set the operating parameters: chromatographic column: Eclipse XDB-C18 (150mm×4.6mm×5μm); flow rate: 0.8mL / min; column temperature: 40℃; injection volume: 20μL; mobile phase A: secondary water; mobile phase B: acetonitrile; elution program: gradient elution program: 0-10min, A linearly increased from 5% to 70%, maintained for 4min; diode array detector, detection wavelength 336nm; quantitative method: external standard method; start and monitor the instrument operation status, including injection volume, column temperature changes, etc. The obtained liquid chromatogram of drometrizole is as follows: Figure 1 shown.

[0072] 1.5 Pre-treatment

[0073] The above textiles were cut into 5 mm × 5 mm pieces, 1.0 g of positive samples were weighed into a glass extractor, 30 mL of chromatographically pure acetonitrile was added, and extraction was performed in an ultrasonic generator at 40 °C for 60 min. After the extract was cooled, it was filtered using a 0.45 μm organic phase filter membrane and analyzed using a high performance liquid chromatography-diode array detector (LC-DAD).

[0074] 2 Results Analysis

[0075] 2.1 Optimization of liquid chromatography instrument conditions

[0076] 2.1.1 Determination of DAD detection wavelength

[0077] Dromtriazole has strong absorption in the ultraviolet spectrum. DAD was used to perform a full spectrum scan analysis on a standard solution of Dromtriazole with a mass concentration of 50 μg / mL. The results are as follows: Figure 2shown.

[0078] Depend on Figure 2 It can be seen that drometrizole has characteristic absorption at 298 nm and 336 nm, the absorption intensity at 336 nm is higher than that at 298 nm, and the absorption peak is sharp, so 336 nm is set as the detection wavelength of drometrizole.

[0079] 2.1.2 Selection of mobile phase

[0080] Dromtriazole is easily soluble in methanol or acetonitrile organic solvents. In addition, the cutoff absorption wavelengths of methanol and acetonitrile are 205nm and 190nm, respectively, which have little interference with the detection of dromtriazole. Therefore, the effects of methanol-water mobile phase system and acetonitrile-water mobile phase system on the detection of dromtriazole were investigated. The results are as follows: Figure 3 shown.

[0081] Depend on Figure 3 It can be seen that the methanol-water mobile phase system and the acetonitrile-water mobile phase system have a significant effect on the peak area and retention time of the chromatographic peak of drometrizole. The chromatographic peak of drometrizole is sharper and the retention time is shorter under the acetonitrile-water mobile phase system, so the acetonitrile-water mobile phase system is selected.

[0082] The addition of organic acid usually improves the chromatographic peak morphology. This experiment investigated the effects of acetonitrile-water mobile phase system and acetonitrile-0.1% formic acid mobile phase system on the chromatographic peak of drometrizole. Figure 4 shown.

[0083] Depend on Figure 4 It can be seen that the addition of formic acid has little effect on the chromatographic peak morphology of drometrizole and little effect on the retention time, so the acetonitrile-water mobile phase system is still selected.

[0084] 2.1.3 Determination of column temperature

[0085] The column temperatures were selected at 25, 30, 35 and 40 °C, respectively, to investigate the effect of different column temperatures on the retention time of the chromatographic peak of drometrizole. The retention time is shown in Table 1:

[0086] Table 1 Effect of column temperature on retention time of drometrizole chromatographic peak

[0087]

[0088] The results show that the column temperature has a significant effect on the retention time. Increasing the temperature will reduce the viscosity of the mobile phase, which will advance the retention time of the chromatographic peak of drometrizole and improve the analysis efficiency. At the same time, the change of column temperature has little effect on the peak area of ​​the chromatographic peak of drometrizole. After comprehensive consideration, the column temperature was determined to be 40℃, which can achieve rapid detection of drometrizole.

[0089] 2.2 Optimization of pre-processing

[0090] 2.2.1 Selection of extraction solvent

[0091] The chemical structure of drometrizole contains hydroxyl groups, so it has a certain polarizability and is soluble in organic reagents such as alcohols and acetonitrile. Methanol, n-hexane, acetonitrile, acetone, ethyl acetate, toluene, methyl tert-butyl ether and tetrahydrofuran were used as extraction solvents to extract the positive samples of nylon / polyester blended fabrics in an ultrasonic water bath at 40°C for 60 minutes to explore the effect of the type of extraction solvent on the normalized extraction efficiency of drometrizole. The results are shown in Table 2:

[0092] Table 2 Effect of extraction solvent type on normalized extraction efficiency of drometrizole in positive samples of nylon / polyester blended fabrics

[0093]

[0094] As shown in Table 2, when acetonitrile and tetrahydrofuran are used as extraction solvents, the normalized extraction efficiency of drometrizole is greater than 95%. However, a large amount of tetrahydrofuran and long-term use will affect the life of the C18 chromatographic column and will also corrode the polyetheretherketone material components in the liquid chromatography flow path. After comprehensive consideration, acetonitrile was selected as the extraction solvent.

[0095] 2.2.2 Comparison of extraction methods and solid-liquid ratio

[0096] Acetonitrile was used as the extraction solvent, and ultrasonic extraction was used at 40°C for 60 minutes to extract the positive samples of nylon / polyester blended fabrics, and the effect of different solid-liquid ratios on the normalized extraction efficiency was investigated. The highest value of drometrizole detection was used as the denominator for normalization, and the normalized extraction efficiency of each extraction method was obtained. The results are shown in Table 3:

[0097] Table 3 Effects of extraction method and solid-liquid ratio on the normalized extraction efficiency of drometrizole in positive samples of nylon / polyester blended fabrics

[0098]

[0099] As shown in Table 3, the normalized extraction efficiency is the highest when the solid-liquid ratio is 1:50, and the normalized extraction efficiency difference between 1:30 and 1:50 is very small, which can meet the experimental requirements. For the same instrument detection limit, the larger the solid-liquid ratio, the lower the method detection limit, and samples with lower content can be detected. Therefore, ultrasonic extraction with a solid-liquid ratio of 1:30 is the best extraction method.

[0100] 2.2.3 Determination of extraction temperature

[0101] Acetonitrile was used as the extraction solvent with a solid-liquid ratio of 1:30 and an extraction time of 60 min. The normalized extraction efficiency of drometrizole in positive samples of nylon / polyester blended fabrics was determined at extraction temperatures of 20, 30, 40, 50°C and 60°C to explore the effect of different extraction temperatures on the normalized extraction efficiency of drometrizole.

[0102] like Figure 5 As shown in the figure, the extraction efficiency of drometrizole increases linearly with the increase of extraction temperature, and the extraction efficiency is basically stable when it reaches 40℃, so 40℃ is determined to be the optimal extraction temperature.

[0103] 2.2.4 Determination of extraction time

[0104] Acetonitrile was used as the extraction solvent, the solid-liquid ratio was 1:30, and the extraction temperature was 40°C. The normalized extraction efficiency of drometrizole in positive samples of nylon / polyester blended fabrics was determined at extraction times of 30, 60, 90, 120 and 180 min, and the effects of different extraction times on the normalized extraction efficiency of drometrizole were compared.

[0105] like Figure 6 As shown in the figure, when the extraction time increases from 30 min to 60 min, the normalized extraction efficiency of drometrizole shows a significant upward trend, and there is no significant increase in the normalized extraction efficiency after 60 min. Considering the time cost factor, 60 min is determined to be the optimal extraction time.

[0106] 2.3 Method linearity and detection limit

[0107] The standard curve was drawn with the concentration of drometrizole as the abscissa and the peak area of ​​the chromatographic peak as the ordinate, and the linear correlation coefficient was 0.9996. After the reagent blank was added with the standard solution to complete the pretreatment step, the instrument analysis was performed. When the signal-to-noise ratio was 3, the corresponding concentration was the method detection limit, which was 21.2 mg / kg. The results are shown in Table 4:

[0108] Table 4 Standard curve and detection limit of drometrizole in textiles by HPLC

[0109]

[0110] 2.4 Recovery and precision

[0111] Three concentrations of drometrizole standard solution were added to nylon / polyester blended fabrics to make the sample content 300, 900 and 1500 mg / kg, and each concentration was repeated 7 times. As shown in Table 5, the recovery rate was 94.1% to 97.4%, and the relative standard deviation was 3.4% to 5.9%, which met the daily detection requirements.

[0112] Table 5 Recovery and precision of drometrizole in textiles

[0113]

[0114] 3 Conclusion

[0115] The optimal instrumental analysis conditions were determined by optimizing the detection wavelength, mobile phase system and column temperature of the liquid chromatograph DAD detector, and the optimal pretreatment conditions were determined by comparing the effects of changes in extraction solvent, extraction temperature and extraction time on the results of drometrizole. The mass concentration of drometrizole has a good linear relationship in the range of 10-50μg / mL, the method detection limit is 21.2mg / kg, the recovery rate is 94.1%-97.4%, and the relative standard deviation is 3.4%-5.9%.

[0116] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the technical solution of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for determining drometrizole in textiles, characterized in that: The following steps are involved: S1. Preparation of standard solution Preparation of standard stock solution: Dissolve drometrizole in chromatographically pure tetrahydrofuran and dilute to volume in a brown volumetric flask to obtain a standard stock solution; Preparation of standard working solution: Take different volumes of drometrizole standard stock solution and place them in multiple brown volumetric flasks, and dilute to volume with chromatographic pure methanol to obtain standard working solutions with different mass concentrations; S2. Preparation of positive samples Select a nylon / polyester blended textile that is tested to be free of drometrizole, soak it in the standard working solution prepared in step S1, and then place it in a constant temperature forced air drying oven for drying, wherein the sample is periodically stirred with a glass rod to make drometrizole evenly attached to the fabric sample, to obtain a positive sample; S3. Preparation of test solution The positive sample obtained in step S2 is cut into pieces and placed in a glass extractor, and an extraction solvent is added to the glass extractor for extraction; the extract is cooled and filtered with an organic phase filter membrane to obtain a test solution; S4. Determination of drometrizole The solution to be tested obtained in step S3 is subjected to liquid chromatography analysis to determine the content of drometrizole in the solution to be tested.

2. The method for determining drometrizole in a textile according to claim 1, characterized in that: In S1, the mass concentration of drometrizole in the prepared standard stock solution was 800 μg / mL; the mass concentrations of drometrizole in the prepared standard working solutions were 10.0, 20.0, 30.0, 40.0, and 50.0 μg / mL, respectively.

3. The method for determining drometrizole in a textile according to claim 1, characterized in that: In S2, the positive samples were dried in a forced air drying oven at a constant temperature of 75°C for 3 h, with a stirring cycle of 15 min / time.

4. The method for determining drometrizole in a textile according to claim 1, characterized in that: In S3, the solid-liquid ratio of the positive sample and the extraction solvent in the glass extractor is 1:30-50; the extraction solvent is any one of methanol, n-hexane, acetonitrile, acetone, ethyl acetate, toluene, methyl tert-butyl ether, and tetrahydrofuran; the extraction method is ultrasonic extraction, the extraction temperature is 20-60°C, and the extraction time is 30-60min.

5. The method for determining drometrizole in a textile according to claim 4, characterized in that: The solid-liquid ratio is 1:30; the extraction solvent is acetonitrile, the extraction temperature is 40°C; the extraction time is 60 minutes; and the pore size of the organic phase filter membrane is 0.45 μm.

6. The method for determining drometrizole in a textile according to claim 1, characterized in that: In S4, a high performance liquid chromatograph-diode array detector (LC-DAD) is used for liquid chromatography analysis, wherein the conditions for the liquid chromatography analysis are: Chromatographic column: Eclipse XDB-C18 (150 mm × 4.6 mm × 5 μm); Flow rate: 0.8 mL / min; Column temperature: 25-40°C; Injection volume: 20 μL; Mobile phase A: secondary water; Mobile phase B: methanol or acetonitrile; Elution program: Gradient elution program: 0-10min, A linearly increased from 5% to 70%, maintained for 4min; Diode array detector, detection wavelength is 298~336nm; Quantitative method: external standard method.

7. The method for determining drometrizole in a textile according to claim 6, characterized in that: The column temperature was 40°C; the mobile phase B was acetonitrile; and the detection wavelength was 336 nm.

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