Method for measuring content of methylhydrazine through precolumn derivatization-high performance liquid chromatography

Abstract

The invention provides a method for determining the content of methylhydrazine by pre-column derivatization-high performance liquid chromatography, which comprises the following steps: S1, uniformly mixing a methylhydrazine hydrate sample solution, 9-fluorenylmethoxycarbonyl chloride and an alkaline solution, standing for 20-50 minutes at room temperature to perform a derivatization reaction, and adding an acid solution to terminate the reaction; and S4, detecting the sample derived in the S1, establishing a chromatogram of methylhydrazine in the sample solution to be detected, obtaining a chromatogram retention time range of methylhydrazine, and calculating the content of methylhydrazine in the methylhydrazine hydrate according to the standard curve fitted in the S3. The pretreatment method is simple, the reaction condition is mild, the reaction rate is high, the detection sensitivity is high, the methylhydrazine derivative generated in a pre-column derivatization mode has ultraviolet absorption, a methylhydrazine derivative peak can be separated from a 9-fluorenylmethoxycarbonyl chloride chromatographic peak through reversed-phase high performance liquid chromatography, and detection of methylhydrazine is not interfered.

Description

Technical Field

[0001] The invention relates to the field of chemical detection and analysis, and in particular to a high performance liquid chromatography column pre-derivation method for detecting methylhydrazine. Background Art

[0002] Methylhydrazine is an important chemical raw material. It can be used as a reducing agent, controlling agent, buffer and catalyst, etc. It is widely used in the semiconductor industry, dye industry, pesticide industry and pharmaceutical industry. The production process of methylhydrazine is often accompanied by by-products 1,1-dimethylhydrazine and unreacted hydrazine hydrate. These three chemical substances have similar structures, which affects the quality control of methylhydrazine products.

[0003] At present, the detection methods of methylhydrazine include titration, spectrophotometry, gas chromatography and hydrophilic chromatography-mass spectrometry. Xu Linnan et al. used hydrophilic chromatography-mass spectrometry to analyze the content of methylhydrazine, hydrazine hydrate and 1,1-dimethylhydrazine, but the sensitivity of this method varies greatly, which is not conducive to large-scale promotion. The National Environmental Protection Standard of the People's Republic of China (HJ674-2013) - Determination of Hydrazine and Methylhydrazine in Water Quality - Dimethylaminobenzaldehyde Spectrophotometry uses dimethylaminobenzaldehyde spectrophotometry to determine methylhydrazine in water quality, but this method has problems such as complex sample pretreatment, long analysis time and many interference factors.

[0004] High performance liquid chromatography-ultraviolet detection is a common and widely used analytical method, but methylhydrazine has a simple molecular structure and no conjugated structure, and has a low response in the ultraviolet detector, so it cannot be directly determined using conventional ultraviolet detector-high performance liquid chromatography. Summary of the invention

[0005] The invention aims to provide a method for determining the content of methylhydrazine by pre-column derivatization-high performance liquid chromatography, which can separate methylhydrazine, hydrazine hydrate and 1,1-dimethylhydrazine and detect the content of methylhydrazine quickly and accurately.

[0006] The present invention provides a method for determining the content of methylhydrazine by pre-column derivatization-high performance liquid chromatography, comprising the following steps: S1: Take a certain concentration of methylhydrazine hydrate sample solution, 9-fluorenylmethoxycarbonyl chloride and alkaline solution in a molar ratio of 1:3-4:27-36 and add them in a certain order, mix them evenly, stand at room temperature for 20-50 minutes to complete the derivatization, and then add an acidic solution until the pH is acidic (adjust the pH to 3-5) to terminate the reaction; S2: Using methylhydrazine sulfate as a control sample instead of methylhydrazine hydrate in S1, the sample was dissolved in water to prepare a standard sample solution with a concentration gradient, and treated in the same manner as S1; S3: After filtering the gradient concentration standard solution after derivatization in S2 through a filter membrane, the methylhydrazine derivative is detected by a UV detector to obtain the peak area of ​​methylhydrazine standard samples with different concentrations, and a standard curve is fitted; S4: testing the sample derived in S1, establishing a chromatogram of methylhydrazine in the sample solution to be tested, obtaining the chromatogram retention time range of methylhydrazine, and calculating the content of methylhydrazine in methylhydrazine hydrate according to the standard curve fitted in S3.

[0007] Furthermore, the mass concentration of methylhydrazine hydrate in S1 is 400-500 ppm.

[0008] Furthermore, the mass concentration of 9-fluorenylmethoxycarbonyl chloride in S1 is 0.6 g / L-2 g / L.

[0009] Furthermore, the mass concentration of the alkaline solution in S1 is 2%-4%, and the alkaline solution is sodium borate; the mass concentration of the acidic solution is 50%-80%, and the acidic solution is sulfuric acid, phosphoric acid or hydrochloric acid.

[0010] Furthermore, the water used for the methylhydrazine hydrate, methylhydrazine sulfate, alkaline solution and acidic solution in S1 and S2 is ultrapure water with a resistivity of 18.25 MQ·cm. The solvent for 9-fluorenylmethoxycarbonyl chloride is a nitrile reagent.

[0011] Furthermore, the filter membrane in S3 is a special filter membrane for liquid chromatography, with a pore size of 0.45 μm.

[0012] Further, the separation chromatographic conditions of the methylhydrazine derivatives are as follows: Chromatographic column: Reversed phase chromatographic column with octadecylsilane bonded silica gel as filler; Mobile phase A: acetonitrile; Mobile phase B: 0.1-0.5% phosphoric acid aqueous solution; Gradient elution: 0-3min, the volume percentage of mobile phase A is 25%-35%; The volume percentage of mobile phase A increased from 25%-35% to 45%-55% from 3 to 11 min; From 11 to 16 min, the volume percentage of mobile phase A was maintained at 45% to 55%; The volume percentage of mobile phase A was reduced from 45%-55% to 25%-35% at 16-20min; The volume percentage of mobile phase A is maintained at 25%-35% for 20-22 min; Detection wavelength: 264nm-268nm; Column temperature: 25-35°C; Flow rate: 0.5-1.0mL / min; Injection volume: 5-15μL.

[0013] Technical Effects In the present invention, phosphoric acid water and acetonitrile solution are used as mobile phases, and a gradient elution method is adopted, so that the separation effect of methylhydrazine derivatives and 9-fluorenylmethoxycarbonyl chloride is good, and the peak shape of the methylhydrazine derivative is normally distributed and sharp.

[0014] The invention provides a pre-column derivatization-high performance liquid chromatography method for directly determining the content of a methylhydrazine sample. The pretreatment method is simple, the reaction conditions are mild, the reaction rate is fast, and the detection sensitivity is high. The methylhydrazine derivatives generated by the pre-column derivatization method have ultraviolet absorption, and the reversed-phase high performance liquid chromatography can separate the methylhydrazine derivative peak from the 9-fluorenylmethoxycarbonyl chloride chromatographic peak, and does not interfere with the detection of methylhydrazine. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 .Methylhydrazine standard curve of Example 1.

[0016] Figure 2 .High performance liquid chromatography test spectrum of the methylhydrazine sample in Example 1.

[0017] Figure 3 .High performance liquid chromatography test spectrum of methylhydrazine sample in Example 2.

[0018] Figure 4 .High performance liquid chromatography test spectrum of the methylhydrazine sample in Example 3.

[0019] Figure 5 .High performance liquid chromatography test spectrum of methylhydrazine sample in Example 4.

[0020] Figure 6 .High performance liquid chromatography test spectrum of methylhydrazine sample in Example 5. DETAILED DESCRIPTION

[0021] The scheme of the present invention is described specifically and clearly below in conjunction with embodiments.

[0022] Example 1 A high performance liquid chromatography column pre-derivation method for detecting methylhydrazine, the specific steps are as follows: (1) Solution preparation Sodium tetraborate solution: 2% (w / w) sodium borate aqueous solution.

[0023] Phosphoric acid solution: 10% (w / w) phosphoric acid in water.

[0024] 9-Fmocyl chloride solution: Take an appropriate amount of 9-Fmocyl chloride solid, add acetonitrile to dissolve and dilute to a 2 mg / mL 9-Fmocyl chloride solution.

[0025] Methylhydrazine sample solution: Take an appropriate amount of methylhydrazine hydrate, dissolve it in water and dilute it to a 500 ppm methylhydrazine solution.

[0026] Methylhydrazine sulfate solution: Take an appropriate amount of methylhydrazine sulfate, dissolve it in water and dilute it into a 500 ppm methylhydrazine solution.

[0027] (2) Preparation of derivatization solution Methylhydrazine sulfate derivatization solution: Mix methylhydrazine sulfate solution, 9-fluorenylmethoxycarbonyl chloride solution and sodium tetraborate solution in a molar ratio of 1:4:36, react at room temperature for 30 minutes, then add 80% phosphoric acid solution to adjust the pH to 3.0, mix well, and terminate the derivatization reaction.

[0028] Methylhydrazine sample solution: Mix the methylhydrazine sample solution, 9-fluorenylmethoxycarbonyl chloride solution and sodium tetraborate solution in a molar ratio of 1:4:36, react at room temperature for 30 minutes, then add 80% phosphoric acid solution to adjust the pH to 3.0, mix well, and terminate the derivatization reaction.

[0029] Blank solution: Ultrapure water, 9-Fmocyl chloride solution and sodium tetraborate solution were mixed evenly in a molar ratio of 1:4:36, reacted at room temperature for 30 min, and then 1 μL of 80% phosphoric acid solution was added to adjust the pH to 3.0, mixed evenly, and the derivatization reaction was terminated.

[0030] (3) Preparation of standard solution A 500ppm methylhydrazine sulfate (φ=98%) solution was diluted with ultrapure water to prepare standard solutions with concentrations of 100ppm, 200ppm, 300ppm, 400ppm and 500ppm, respectively. The prepared methylhydrazine standard solutions of various concentrations were mixed evenly with 9-fluorenylmethoxycarbonyl chloride solution and sodium tetraborate solution in a molar ratio of 1:4:36, and reacted at room temperature for 30min. A phosphoric acid solution with a mass concentration of 80% was then added to adjust the pH to 3.0, and mixed evenly to terminate the derivatization reaction. The treated methylhydrazine standard solution was filtered through a 0.45 μm organic filter membrane and then placed in a 2 mL sample bottle. The methylhydrazine derivatives were passed through an ultraviolet detector to generate signals, and the chromatographic peaks and peak areas of the methylhydrazine derivatives were obtained. The peak areas were 199940, 423613, 652951, 898189, and 1107944 mAV·s, respectively. The standard curve of methylhydrazine was obtained with the peak area of ​​the methylhydrazine derivatives as the ordinate and the concentration of the methylhydrazine standard sample as the abscissa. The regression equation and linear correlation coefficient of the standard curve were: y=2290.6x-30648, r 2 =0.9996. Use Excel to make a standard curve, see Figure 1 .

[0031] (4) Chromatographic conditions Chromatographic column: Reversed phase chromatographic column with octadecylsilane bonded silica gel as filler; Detector: UV detector; Column temperature: 25°C; Flow rate: 1.0 mL / min; Mobile phase A: 0.1% phosphoric acid in water (w / w); Mobile phase B: acetonitrile, chromatographic grade; The gradient elution settings were:

[0032] (5) Determination method The methylhydrazine sample derivatization solution prepared in (2) was filtered through a 0.45 μm organic filter membrane and placed in a 2 mL sample bottle. The peak area was 351218 mAV·s after detection by HPLC-UV detector. Figure 2 The content of methylhydrazine was accurately calculated to be 31.38% by the external standard method. The above test completes the HPLC analysis of methylhydrazine through a derivatization reaction. The derivatization process is simple to operate. The methylhydrazine derivatization peak is symmetrical and separated from the peak of the derivatization reagent, which can quickly, efficiently and accurately measure the content of methylhydrazine.

[0033] Example 2 The detection method and conditions were the same as those in Example 1, except that the methylhydrazine sample was not derivatized and was directly detected by UV-HPLC.

[0034] Results: The methylhydrazine sample did not show any peak under the test conditions, and only the solvent peak was found in the chromatogram. Figure 3 .

[0035] Example 3 The detection method and conditions were the same as those in Example 1, except that the gradient elution in the chromatographic conditions was set to isocratic elution.

[0036] The isocratic elution settings are:

[0037] Results: The methylhydrazine derivative peaked at 4.268 min, which was earlier and very close to the peak of 9-Fmocyl chloride, making it difficult to accurately detect the methylhydrazine sample. Figure 4 .

[0038] Example 4 The detection method and conditions were the same as those in Example 1, except that the derivatization time of the methylhydrazine sample was shortened to 5 min, and then acid was directly added for quenching.

[0039] Results: The results were similar to those in Example 2. No methylhydrazine derivative peak appeared. The chromatographic peak of 9-fluorenylmethoxycarbonyl chloride appeared at 14.435 min. Figure 5 The reason is presumably that the derivatization of the sample cannot be achieved in a short period of time at room temperature and in an alkaline environment of 2% sodium borate.

[0040] Example 5 The detection method and conditions were the same as those in Example 1, except that the elution gradient during the detection process was changed. The specific gradient settings were as follows:

[0041] Results: Chromatogram see Figure 6 , 13.433min is the chromatographic peak of 9-fluorenylmethoxycarbonyl chloride. Compared with the standard sample, 12.907min is identified as the methylhydrazine derivative peak. The unseparated chromatographic peak of 12.733min may be 1,1-dimethylhydrazine and other impurity components with similar structure to methylhydrazine. The separation degree of the two chromatographic peaks is less than 1.

[0042] In summary, after derivatization pretreatment, a reverse phase chromatographic column (such as Hypersil GOLD C18, etc.) with octadecylsilane bonded silica gel as a filler is used, the mobile phase is acetonitrile and 0.1% phosphoric acid aqueous solution, the flow rate is 1.0 mL / min, the detection wavelength is 266 nm, and under the gradient elution of Example 1, methylhydrazine has a strong signal under the ultraviolet detector, and has a good separation effect from other impurities. The chromatographic peak shape is sharp and symmetrical, and the quantification of methylhydrazine can be accurately and quickly achieved.

Claims

1. A method for determining the content of methylhydrazine by pre-column derivatization-high performance liquid chromatography, characterized in that: The following steps are involved: S1: Take the methylhydrazine hydrate sample solution, 9-fluorenylmethoxycarbonyl chloride and the alkaline solution and mix them evenly, let them stand at room temperature for 20-50 minutes for derivatization reaction, and then add the acidic solution to terminate the reaction; S2: Methylhydrazine sulfate was used as a control sample, dissolved in water to prepare a standard sample solution with a concentration gradient, and the standard sample solution was used to replace the methylhydrazine hydrate in S1, and the derivatization treatment was performed in the same manner as S1; S3: After filtering the derivatized gradient solution in S2 through a filter membrane, the methylhydrazine derivative is detected by a UV detector to obtain the peak areas of methylhydrazine standards with different concentrations, and a standard curve is fitted; S4: testing the sample derived in S1, establishing a chromatogram of methylhydrazine in the sample solution to be tested, obtaining the chromatogram retention time range of methylhydrazine, and calculating the content of methylhydrazine in methylhydrazine hydrate according to the standard curve fitted in S3.

2. The method according to claim 1, characterized in that: The molar ratio of the methylhydrazine hydrate sample solution, 9-fluorenylmethoxycarbonyl chloride and the alkaline solution in S1 is 1:3-4:27-36; The mass concentration of the methylhydrazine hydrate is 400-500 ppm; the mass concentration of 9-fluorenylmethoxycarbonyl chloride is 0.6 g / L-2 g / L.

3. The method according to claim 2, characterized in that: The mass concentration of the alkaline solution in S1 is 2%-4%, and the alkaline solution is sodium borate.

4. The method according to claim 3, characterized in that: The mass concentration of the acidic solution in S1 is 50%-80%, and the acidic solution is sulfuric acid, phosphoric acid or hydrochloric acid; the acidic solution is added to adjust the pH of the reaction solution of the derivatization reaction to 3-5 and then terminate the reaction.

5. The method according to claims 2-4, characterized in that: The water used for methylhydrazine hydrate, methylhydrazine sulfate, alkaline solution and acidic solution is ultrapure water with a resistivity of 18.25MQ·cm; the solvent for 9-fluorenylmethoxycarbonyl chloride is a nitrile reagent, and the nitrile reagent includes acetonitrile.

6. The method according to claim 1, characterized in that: The filter membrane in S3 is a special filter membrane for liquid chromatography with a pore size of 0.45μm.

7. The method according to claim 1, characterized in that: The separation chromatographic conditions of methylhydrazine derivatives are as follows: Chromatographic column: Reversed phase chromatographic column with octadecylsilane bonded silica gel as filler; Mobile phase: acetonitrile as mobile phase A, 0.1-0.5% w / w phosphoric acid aqueous solution as mobile phase B, gradient elution; Detection wavelength: 264nm-268nm; Column temperature: 25-35°C; Flow rate: 0.5-1.0mL / min; Injection volume: 5-15μL.

8. The method according to claim 7, characterized in that: The specific settings for gradient elution are: The volume percentage of mobile phase A from 0 to 3 min is 25% to 35%; The volume percentage of mobile phase A increased from 25%-35% to 45%-55% from 3 to 11 min; From 11 to 16 min, the volume percentage of mobile phase A was maintained at 45% to 55%; The volume percentage of mobile phase A was reduced from 45%-55% to 25%-35% at 16-20min; The volume percentage of mobile phase A was maintained at 25%-35% for 20-22 minutes.

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