A method for determining the content of octadecylamine in potassium chloride solid samples

Abstract

The present invention discloses a method for determining the content of octadecylamine in a solid potassium chloride sample. Step 1: Prepare a determination system; the determination system includes a potassium chloride standard, a water-soluble indicator solution, a buffer solution, and an octadecylamine standard stock solution that are independent of each other. Step 2: Plot a standard curve: Use the concentration of each octadecylamine standard solution as the abscissa and its corresponding absorbance as the ordinate to plot the standard curve. Step 3: Determine the content of octadecylamine: Calculate the content of octadecylamine in the potassium chloride sample to be measured through the standard curve. The determination system of the present invention has low toxicity and can effectively improve the accuracy of the determination of the content of octadecylamine.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical detection, and particularly to a method for determining the content of octadecylamine in a potassium chloride solid sample. Background Art

[0002] When producing potassium chloride by the method of cold crystallization - positive flotation, the flotation agent octadecylamine combines with potassium chloride particles in the carnallite decomposition slurry, and the potassium chloride particles are floated out by air bubbling. Therefore, the obtained potassium chloride product will inevitably contain the flotation agent octadecylamine, which has an adverse effect on the development of high - value potassium chloride products.

[0003] Hu Jiayuan et al. (CN102062728B) provided a method for determining the concentration of octadecylamine without adding a chromogenic agent. Glacial acetic acid was added to the solution to be measured, and the absorbance in the ultraviolet region was directly measured, which could effectively measure octadecylamine in the content range of 10 - 50 mg / L. Octadecylamine has low solubility in water, and due to the salting - out effect, its solubility in high - concentration potassium chloride is even smaller. This method is not suitable for determining the content of low - content octadecylamine.

[0004] Evtushenko et al. used methyl orange as a chromogenic agent at pH = 2.5 to directly measure the absorbance value to obtain the concentration of octadecylamine in water. Sun Deshun et al. first added salicylaldehyde to react with octadecylamine to form salicylaldimine, and then added bromocresol green for color development to measure the absorbance value to obtain the content of octadecylamine. For the above two methods without using an extractant, chromogenic agents were added. Since the chromogenic agent itself has absorbance, an excessive and inaccurate amount is usually added during the measurement process, which easily causes background interference to the absorbance measurement of the complex, resulting in a decrease in measurement precision, especially for low - content samples, the measurement error is relatively large.

[0005] Ronald M. Silverstein used methyl orange as a chromogenic agent and chloroform, dichloroethane, and diethyl ether as extractants to determine the amine content in the boiler system water. The national electric power industry standard "Determination of Alkyl Octadecylamine in Water" (DL / T1042.2007) in China also recommends using methyl orange as a complexing chromogenic agent, and at pH = 3 - 4, chloroform extraction and spectrophotometry are used to determine octadecylamine in power plant boiler wastewater.

[0006] When determining the octadecylamine, a potassium fertilizer flotation agent, Liang Huibin used gas chromatography and auramine-2 spectrophotometry respectively to determine the content of octadecylamine hydrochloride in a saturated potassium chloride solution. When using gas chromatography, after chloroform extraction, solvent evaporation and concentration were still required. The determination process was cumbersome and the evaporation of chloroform caused air pollution. When using auramine-2 spectrophotometry, the detection limit of the determination was low, which was suitable for the determination of the content of octadecylamine hydrochloride in a pure potassium chloride solution. In an actual potassium chloride system, magnesium and calcium ions were often contained, and auramine-2 would form precipitates with magnesium and calcium ions in the solution, affecting its complexation and color development with octadecylamine, resulting in inaccurate determination and being not applicable to the actual system.

[0007] Diao Xiangrui et al. used bromocresol green spectrophotometry to determine the content of octadecylamine in potassium chloride. When drawing the standard curve, the amount of color-developing agent added to different concentrations of octadecylamine solutions was different, and the ratio of the organic phase to the aqueous phase was not fixed during the chloroform extraction step. If this method was used to determine an unknown sample, the amount of color-developing agent used could not be determined, and the influence on the extraction efficiency and the entire analysis process could not be determined either, so the accuracy could not be guaranteed when determining actual samples. Since octadecylamine was highly soluble in chloroform, chloroform was used as the extraction agent in the above methods. However, chloroform was extremely volatile and had the possibility of causing cancer. It was sensitive to light, could be decomposed into highly toxic phosgene, and was controlled by dangerous chemicals and precursor chemicals.

[0008] Li Bing used methyl orange as the color-developing agent and ethyl acetate instead of chloroform as the extraction agent to determine the content of octadecylamine in water. Ethyl acetate had low toxicity, but ethyl acetate had a certain solubility in water (0.1 mL / mL) and would undergo a certain degree of hydrolysis. When used to extract the methyl orange-octadecylamine complex, the recovery rate might not be high and the determination result might be on the low side.

[0009] At present, when using spectrophotometry to determine low-content octadecylamine, chloroform is mainly used as the extraction agent. Chloroform is extremely volatile and will quickly volatilize in each step of the determination operation, resulting in affected determination accuracy and low determination precision. In addition, chloroform has the possibility of causing cancer, is sensitive to light, can be decomposed into highly toxic phosgene, poses a health threat to the determination experimenters, and chloroform is controlled by dangerous chemicals and precursor chemicals, and there are strict requirements for purchase, use and storage. When using ethyl acetate instead of chloroform as the extraction agent, ethyl acetate has low toxicity, but ethyl acetate has a certain solubility in water (0.1 mL / mL). When used to extract the methyl orange-octadecylamine complex, the recovery rate might not be high and the determination result might be on the low side.

[0010] When bromocresol green is used as an indicator, since bromocresol green has low solubility in water, it is usually dissolved and prepared with ethanol. The present invention uses a water-soluble indicator as a chromogenic agent and is dissolved and prepared with distilled water, avoiding the introduction of ethanol into the measurement system, reducing the solubility of the octadecylamine complex in the aqueous phase, and further improving the accuracy of the measurement method.

[0011] When usually determining the content of components or impurities in soluble solids, after dissolving the solid sample first, the content of components in the aqueous solution is measured. When producing potassium chloride by the cold crystallization - positive flotation method, the flotation agent octadecylamine adsorbs on the surface of potassium chloride particles and is separated from the liquid phase in the form of foam through hydrophobic interaction. If the potassium chloride sample to be measured is directly dissolved in water, since octadecylamine has very low solubility in water and its solubility is even smaller in high-concentration potassium chloride due to the salting-out effect, the octadecylamine in potassium chloride cannot be completely dissolved, but adsorbs on the container wall through hydrophobic interaction and cannot be completely transferred into the measurement system, which may result in a low measurement result. Summary of the Invention

[0012] The object of the present invention is to address the technical defects existing in the prior art. The present invention provides a method for determining the content of octadecylamine in a potassium chloride solid sample, using a water-soluble indicator as a chromogenic agent and extracting and coloring with a long-chain alkane or a long-chain halogenated alkane.

[0013] The technical solution adopted to achieve the object of the present invention is as follows:

[0014] A method for determining the content of octadecylamine in a potassium chloride solid sample, comprising the following steps:

[0015] Step 1, prepare the measurement system:

[0016] The measurement system includes an independent potassium chloride standard product (preferably of analytical reagent grade), a water-soluble indicator solution, a buffer solution, and an octadecylamine standard stock solution. Among them, the water-soluble indicator solution is prepared by the following steps: Weigh the water-soluble indicator and make up the volume with distilled water to obtain the water-soluble indicator solution; the pH of the buffer solution is 4.5 - 6.0; the octadecylamine standard stock solution includes a plurality of octadecylamine standard solutions with different concentrations, and the concentrations of the plurality of octadecylamine standard solutions vary in a gradient. It is prepared by the following steps: Accurately weigh a predetermined mass of octadecylamine, dissolve it in a long-chain alkane and make up the volume, and then dilute it respectively to obtain octadecylamine standard solutions with different concentrations.

[0017] Step 2, draw the standard curve:

[0018] Step 2.1, accurately weigh the potassium chloride standard, accurately measure a predetermined volume of buffer solution, water-soluble indicator solution, and distilled water and add them to the potassium chloride standard. Then, add the octadecylamine standard solution according to the volume ratio of organic phase to water phase of (0.05 - 9):1; fully react and extract. After standing and separating layers, using long-chain alkane as the blank, adopt a quartz colorimetric cell to perform absorption spectrum scanning on the organic phase layer in the wavelength range of 800 - 200 nm, select the measurement wavelength. Preferably, the wavelength corresponding to the peak value of absorbance is the measurement wavelength. More preferably, first select the wavelength corresponding to the maximum value of absorbance of the symmetric absorption peak as the measurement wavelength, and perform Steps 1.2 - 1.3. If the obtained standard curve is linear, use this measurement wavelength. If the obtained standard curve is not linear, then select other wavelengths corresponding to the peak values for Steps 1.2 - 1.3 until the standard curve is linear;

[0019] Step 2.2, accurately weigh the potassium chloride standard with the same mass as in Step 2.1, accurately measure the buffer solution, water-soluble indicator solution, and distilled water with the same volume as in Step 2.1 and add them to the potassium chloride standard. Then, add the octadecylamine standard solution with gradient concentrations according to the same volume ratio of organic phase to water phase as in Step 2.1, preferably equal-volume octadecylamine standard solution. Fully react and extract. After standing and separating layers, using long-chain alkane as the blank, adopt a quartz colorimetric cell to measure the absorbance of the organic phase layer at the selected measurement wavelength respectively;

[0020] Step 2.3, use the concentration of each octadecylamine standard solution as the abscissa and its corresponding absorbance as the ordinate to plot the standard curve.

[0021] Step 3, determination of octadecylamine content:

[0022] Accurately weigh the potassium chloride sample to be measured with the same mass as in Step 2.1, accurately measure the buffer solution, water-soluble indicator solution, and distilled water with the same volume as in Step 2.1 and add them to the potassium chloride sample to be measured. According to the same volume ratio of organic phase to water phase as in Step 2.1, add long-chain alkane; fully react and extract. After standing and separating layers, using long-chain alkane as the blank, measure the absorbance of the organic phase layer, and calculate the octadecylamine content in the potassium chloride sample to be measured through the standard curve.

[0023] In the above technical solution, in Steps 2 and 3, dissolution, extraction, and color development are all carried out in the same closed container, preferably a volumetric flask.

[0024] In the above technical solution, the water-soluble indicator is a water-soluble indicator solution with a concentration of 0.1 - 20 g / L.

[0025] In the above technical solution, in the measurement system, the volume ratio of organic phase to water phase is (0.05 - 9):1.

[0026] In the above technical solution, the buffer solution is an acetic acid-sodium acetate buffer solution.

[0027] In the above technical solution, the acetic acid-sodium acetate buffer solution is prepared by the following steps: Weigh anhydrous sodium acetate and dissolve it in distilled water, add acetic acid to adjust the pH of the solution to obtain an acetic acid-sodium acetate buffer solution with a pH of 4.5-6.0.

[0028] In the above technical solution, the water-soluble indicator is sodium bromocresol green, potassium bromocresol green, sodium bromophenol blue or potassium bromophenol blue.

[0029] In the above technical solution, the long-chain alkane is C n H 2n+2 , where n = 7-14. The long-chain alkane is a mixture of one or two or more.

[0030] In the above technical solution, the volume ratio of the buffer solution to the water-soluble indicator solution in the measurement system is (5-100):1. The water-soluble indicator is in excess relative to octadecylamine to ensure complete color development.

[0031] In the above technical solution, the concentration of the octadecylamine standard solution is 0.5 mg / L - 100 mg / L.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. For the determination of the content of low-content substances in a complex system, the accuracy of the determination method determines the quality of the determination method. The present invention uses a long-chain alkane as an extractant, which has good solubility for octadecylamine and the octadecylamine complex of the color-developing agent, is insoluble in water, will not cause loss of octadecylamine extraction, and has low volatility and low toxicity, high determination accuracy, and little harm to the human body and the environment; ethanol is not introduced, and it will not cause loss of the octadecylamine complex of the color-developing agent in water.

[0034] 2. In the determination process of the present invention and the process of drawing the standard curve, the potassium chloride sample is directly added to the color-developing determination system, avoiding the loss of octadecylamine due to hydrophobic adsorption on the container wall during the sample dissolution process. At the same time, when using this determination system, the dissolution, color development, and extraction are all carried out in the same closed container, further improving the accuracy of the octadecylamine content determination.

[0035] 3. The present invention selects a liquid long-chain alkane with low volatility and low toxicity and a carbon chain length as close as possible to that of octadecylamine. The better the similarity solubility with octadecylamine, the better the extraction color development, sensitivity, and accuracy.

[0036] 4. The developer molecule complexes with the octadecylamine molecule to form a macromolecule, which is extracted into the organic phase by alkane for color development through the "like dissolves like" principle. The developer itself cannot be extracted due to insufficient hydrophobicity (shown by the scanning curve when the octadecylamine concentration is 0). Due to the salting-out effect of the complexing molecule, the salt concentration in the solution promotes the complexation of the developer molecule with the octadecylamine molecule to form a macromolecule for extraction. The higher the potassium chloride concentration, the greater the absorbance and the higher the measurement sensitivity. Description of the Drawings

[0037] Figure 1 It is the spectral scanning curve of different contents of octadecylamine in the sodium bromocresol green - heptane system of Example 1.

[0038] Figure 2 It is the standard curve for the determination of octadecylamine in the sodium bromocresol green - heptane system of Example 1.

[0039] Figure 3 It is the spectral scanning curve of different contents of octadecylamine in the potassium bromocresol green - tetradecane system of Example 2.

[0040] Figure 4 It is the standard curve for the determination of octadecylamine in the potassium bromocresol green - tetradecane system of Example 2.

[0041] Figure 5 It is the spectral scanning curve of different contents of octadecylamine in the sodium bromophenol blue - dodecane system of Example 3.

[0042] Figure 6 It is the standard curve for the determination of octadecylamine in the sodium bromophenol blue - dodecane system of Example 3. Detailed Embodiments

[0043] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0044] Example 1

[0045] A method for determining the content of octadecylamine in a potassium chloride solid sample includes the following steps:

[0046] Step 1, potassium chloride sample treatment: Grind the potassium chloride sample so that the particle size of the solid particles is less than 2.5 mm.

[0047] Step 2, prepare the measurement system:

[0048] The determination system includes analytical grade potassium chloride, water-soluble indicator solution, acetic acid-sodium acetate buffer solution, and octadecylamine standard stock solution, which are independent of each other. Among them, the water-soluble indicator solution is prepared by the following steps: Weigh sodium salt of bromocresol green and make up the volume with distilled water to obtain a water-soluble indicator solution with a concentration of 20 g / L; the acetic acid-sodium acetate buffer solution is prepared by the following steps: Weigh anhydrous sodium acetate and dissolve it in distilled water, then add acetic acid to adjust the pH of the solution to obtain an acetic acid-sodium acetate buffer solution with pH = 6.0; the octadecylamine standard stock solution is prepared by the following steps: Accurately weigh 0.5000 g of octadecylamine, dissolve it in C7H 16 and make up the volume to 1 L, and obtain octadecylamine standard stock solutions with concentration gradients through dilution, and the concentrations are 4, 8, 16, 24, 32, and 40 mg / L respectively.

[0049] Step 3, Standard curve plotting:

[0050] Step (1), Accurately weigh 29.9997 g of analytical grade pure potassium chloride and add it to a volumetric flask. Then, accurately measure 75.00 mL of acetic acid-sodium acetate buffer solution, 0.75 mL of water-soluble indicator solution, and 24.25 mL of distilled water and add them to the volumetric flask. The volume ratio of the buffer solution to the water-soluble indicator solution is 100:1; after shaking and dissolving, the concentration of potassium chloride is 300 g / L.

[0051] According to the volume ratio of organic phase to water phase of 0.05:1, add 5.00 mL of octadecylamine standard solution with a concentration of 16 mg / L. Cover the volumetric flask and shake it well. After full reaction and extraction, let it stand for layering, and use C7H 16 as the blank, use a quartz cuvette, and perform spectral scanning on the organic phase layer in the wavelength range of 800 - 200 nm, and select the measurement wavelength to be 624 nm.

[0052] Step (2), Use the same method as in step (1), add 5.00 mL of octadecylamine standard solutions with concentrations of 4, 8, 16, 24, 32, and 40 mg / L respectively, measure the absorbance at 624 nm, and plot the standard curve as shown in the figure.

[0053] Step 4, Octadecylamine content determination:

[0054] Accurately weigh 29.9998 g of the potassium chloride sample to be measured and add it to a volumetric flask. Then, accurately measure 75.00 mL of the buffer solution, 0.75 mL of the water-soluble indicator solution, and 24.25 mL of distilled water and add them to the volumetric flask. The volume ratio of the buffer solution to the water-soluble indicator solution is 100:1; after shaking and dissolving, the concentration of potassium chloride is 300 g / L.

[0055] According to the phase ratio of 0.05:1, add 5.00 mL of C7H 16; Cap the volumetric flask and shake it. After thorough extraction and shaking, let it stand for layering. Using C7H 16 as the blank, measure the absorbance of the organic phase layer. The absorbance is 1.002. Calculate the octadecylamine content in the sample as 6.27 mg / kg through the standard curve.

[0056] Example 2

[0057] A method for determining the octadecylamine content in a potassium chloride solid sample, comprising the following steps:

[0058] Step 1, potassium chloride sample treatment: Grind the potassium chloride sample to make the solid particle size less than 2.5 mm.

[0059] Step 2, prepare the determination system: including analytical grade potassium chloride, water-soluble indicator solution, acetic acid-sodium acetate buffer solution, and octadecylamine standard stock solution that are independent of each other. Among them, the water-soluble indicator solution is prepared by the following steps: Weigh potassium bromocresol green and make up the volume with distilled water to obtain a water-soluble indicator solution with a concentration of 0.1 g / L; the acetic acid-sodium acetate buffer solution is prepared by the following steps: Weigh anhydrous sodium acetate and dissolve it in distilled water, add acetic acid to adjust the pH of the solution to obtain an acetic acid-sodium acetate buffer solution with pH = 4.5; the octadecylamine standard stock solution is prepared by the following steps: Accurately weigh a predetermined mass of octadecylamine, dissolve it in C 14 H 30 and make up the volume to obtain the octadecylamine standard stock solution. Specifically, accurately weigh 0.2000 g of octadecylamine, make up the volume to 500 mL with C 14 H 30 to obtain octadecylamine standard solutions with gradient concentrations through dilution, with concentrations of 8, 16, 32, 64, 80, and 96 mg / L respectively.

[0060] Step 3, standard curve drawing:

[0061] Step (1), accurately weigh 3.0283 g of analytical grade pure potassium chloride and add it to a volumetric flask. Then, accurately measure 5.00 mL of acetic acid-sodium acetate buffer solution, 1.00 mL of water-soluble indicator solution, and 4.00 mL of distilled water and add them to the volumetric flask in sequence. The volume ratio of the buffer solution to the water-soluble indicator solution is 5:1; after shaking and dissolving, the potassium chloride concentration is 303 g / L.

[0062] According to the volume ratio of the organic phase to the aqueous phase of 9:1, add 90.00 mL of octadecylamine standard stock solution with a concentration of 32 mg / L; cap the volumetric flask and shake it well. After sufficient reaction and extraction, let it stand for layering. Using C 14 H 30 as the blank, use a quartz cuvette to perform an absorption spectrum scan on the organic phase layer from 800 - 200 nm, and select the measurement wavelength as 394 nm;

[0063] Step (2): Using the same method as in step (1), add 90.00 mL of octadecylamine standard stock solutions with concentrations of 8, 16, 32, 64, 80, and 96 mg / L respectively, measure the absorbance at 394 nm, and plot the standard curve.

[0064] Step 4: Determination of octadecylamine content:

[0065] Accurately weigh 3.0279 g of the potassium chloride sample to be tested and add it to a volumetric flask. Then, accurately measure 5.00 mL of acetic acid - sodium acetate buffer solution, 1.00 mL of water - soluble indicator solution, and 4.00 mL of distilled water and add them to the volumetric flask. The volume ratio of the buffer solution to the water - soluble indicator solution is 5:1. After shaking and dissolving, the concentration of potassium chloride is 303 g / L.

[0066] According to the volume ratio of the organic phase to the aqueous phase of 9:1, add 90.00 mL of C 14 H 30 ; After covering the volumetric flask and shaking, fully extract and shake well, and then let it stand for layering. Using C 14 H 30 as the blank, measure the absorbance of the organic phase layer. The absorbance is 0.013. Calculate the octadecylamine content in the sample as 251.43 mg / kg through the standard curve.

[0067] Example 3

[0068] Step 1: Treatment of potassium chloride sample: Grind the potassium chloride sample to make the solid particle size less than 2.5 mm.

[0069] Step 2: Preparation of the measurement system: It includes analytical - grade potassium chloride, water - soluble indicator solution, acetic acid - sodium acetate buffer solution, and octadecylamine standard stock solution that are independent of each other. Among them, the water - soluble indicator solution is prepared by the following steps: Weigh sodium bromophenol blue and make a constant volume with distilled water to obtain a water - soluble indicator solution with a concentration of 10 g / L; the acetic acid - sodium acetate buffer solution is prepared by the following steps: Weigh anhydrous sodium acetate and dissolve it in distilled water, add acetic acid to adjust the pH of the solution to obtain an acetic acid - sodium acetate buffer solution with pH = 5.0; the octadecylamine standard stock solution is prepared by the following steps: Accurately weigh a predetermined mass of octadecylamine, dissolve it in C 12 H 26 and make a constant volume to obtain the octadecylamine standard stock solution. Specifically, accurately weigh 0.5000 g of octadecylamine, use C 12 H 26 to make a constant volume to 500 mL, and obtain octadecylamine standard solutions with concentration gradients through dilution, with concentrations of 2, 4, 8, 16, 20, and 24 mg / L respectively.

[0070] Step 3: Plotting the standard curve:

[0071] Step (1): Accurately weigh 5.9011 g of high-grade pure potassium chloride and add it to a volumetric flask. Then, accurately measure 12.00 mL of acetic acid - sodium acetate buffer solution, 0.50 mL of water-soluble indicator solution, and 7.50 mL of distilled water and add them to the volumetric flask. The volume ratio of the buffer solution to the water-soluble indicator solution is 24:1. After shaking and dissolving, the concentration of potassium chloride is 295 g / L.

[0072] According to the volume ratio of organic phase to aqueous phase of 0.2:1, add 4.00 mL of octadecylamine standard stock solution with a concentration of 16 mg / L. After covering the volumetric flask and shaking it well, after sufficient reaction and extraction, let it stand for layer separation, and use C 12 H 26 as the blank, use a quartz cuvette to perform an absorption spectrum scan on the organic phase layer from 800 - 200 nm, and select the measurement wavelength as 568 nm.

[0073] Step (2): Using the same method as in step (1), add 4.00 mL of octadecylamine standard stock solutions with concentrations of 2, 4, 8, 16, 20, and 24 mg / L respectively, measure the absorbance respectively, draw a standard curve, as shown in the figure.

[0074] To determine the detection limit, measure the absorbance of the blank solution 20 times continuously, and obtain the standard deviation of the absorbance σ = 4.12×10 -4 , according to the detection limit formula D.L. = 3σ / r (r is the slope of the standard curve) recommended by IUPAC, calculate that the detection limit of this standard curve is 3.09×10 -2 mg / L (dodecane). Combining the phase ratio (0.2:1) and the potassium chloride concentration (295 g / L), calculate that the detection limit of this measurement standard curve for the octadecylamine content in potassium chloride products is 2.09×10 -2 mg / kg.

[0075] Step 4: Determination of octadecylamine content:

[0076] Accurately weigh 5.9002 g of the potassium chloride sample to be tested and add it to a volumetric flask. Then, accurately measure 12.00 mL of acetic acid - sodium acetate buffer solution, 0.50 mL of water-soluble indicator solution, and 7.50 mL of distilled water and add them to the volumetric flask. The volume ratio of the buffer solution to the water-soluble indicator solution is 24:1. After shaking and dissolving, the concentration of potassium chloride is 295 g / L.

[0077] According to the volume ratio of organic phase to aqueous phase of 0.2:1, add 4.00 mL of C 12 H 26 ; After covering the volumetric flask and shaking it, after sufficient extraction and shaking, let it stand for layer separation, and use C 12 H 26It was blank. A quartz cuvette was used to measure the absorbance of the organic phase layer. The absorbance was 0.401. The content of octadecylamine in the sample was calculated to be 20.13 mg / kg through the standard curve.

[0078] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for determining the content of octadecylamine in a potassium chloride solid sample, characterized in that, The following steps are involved: Step 1: Prepare the assay system: The assay system comprises a mutually independent potassium chloride standard, a water-soluble indicator solution, a buffer solution, and an octadecylamine standard stock solution, wherein the water-soluble indicator solution is prepared by the following steps: weighing the water-soluble indicator and diluting the solution with distilled water to obtain a water-soluble indicator solution; the pH of the buffer solution is 4.5-6.0; the octadecylamine standard stock solution comprises a plurality of octadecylamine standard solutions of different concentrations, wherein the concentrations of the plurality of octadecylamine standard solutions vary in a gradient, and is prepared by the following steps: accurately weighing a predetermined mass of octadecylamine, dissolving the solution in a long-chain alkane to a fixed volume, and then diluting the solution to obtain octadecylamine standard solutions of different concentrations; Step 2, draw the standard curve: Step 2.1, accurately weigh a potassium chloride standard, accurately measure a predetermined volume of a buffer solution, a water-soluble indicator solution, and distilled water and add them to the potassium chloride standard, then add an octadecylamine standard solution at a volume ratio of (0.05-9):1 between the organic phase and the aqueous phase; fully react and extract, let stand for stratification, and use a long-chain alkane as a blank. Using a quartz cuvette, scan the organic phase layer for absorption spectrum in the wavelength range of 800-200 nm, select a measurement wavelength, and select the wavelength corresponding to the peak absorbance as the measurement wavelength. First, select the wavelength corresponding to the maximum absorbance of the symmetrical absorption peak as the measurement wavelength, and proceed to steps 2.2-2.

3. If the obtained standard curve is linear, use this measurement wavelength. If the obtained standard curve is not linear, select the measurement wavelength corresponding to other peaks and proceed to steps 2.2-2.3 until the standard curve is linear; In step 2.2, accurately weigh the same mass of potassium chloride standard as in step 2.1, accurately measure the same volume of buffer solution, water-soluble indicator solution, and distilled water as in step 2.1, and add them to the potassium chloride standard. Then, according to the same volume ratio of organic phase to aqueous phase as in step 2.1, add octadecylamine standard solution with gradient concentrations to obtain equal volumes of octadecylamine standard solution. After sufficient reaction and extraction, stand for stratification, and measure the absorbance of the organic phase layer at the selected measurement wavelength using a quartz cuvette with a long-chain alkane as a blank; Step 2.3, using the concentration of each octadecylamine standard solution as the abscissa and the corresponding absorbance as the ordinate to draw a standard curve; Step 3, determination of octadecylamine content: Accurately weigh the same mass of the potassium chloride sample to be tested as in step 2.1, accurately measure the same volume of buffer solution, water-soluble indicator solution, and distilled water as in step 2.1 and add them to the potassium chloride sample to be tested, add a long-chain alkane according to the same volume ratio of organic phase to aqueous phase as in step 2.1; fully react and extract, stand and separate, measure the absorbance of the organic phase layer with the long-chain alkane as a blank, and calculate the octadecylamine content in the potassium chloride sample to be tested using the standard curve.

2. The method for determining the content of octadecylamine in a potassium chloride solid sample according to claim 1, characterized in that, In step 2 and step 3, the dissolving, extracting and coloring are all carried out in the same closed container, preferably a volumetric flask.

3. The method for determining the content of octadecylamine in a potassium chloride solid sample according to claim 1, characterized in that, The water-soluble indicator is a water-soluble indicator solution with a concentration of 0.1-20 g / L.

4. The method for determining the content of octadecylamine in a solid potassium chloride sample according to claim 1, characterized in that, In the described determination system, the volume ratio of the organic phase to the aqueous phase is (0.05 - 9):

1.

5. The method for determining the content of octadecylamine in a potassium chloride solid sample according to claim 1, characterized in that, The buffer solution is an acetic acid - sodium acetate buffer solution.

6. The method for determining the content of octadecylamine in a potassium chloride solid sample according to claim 5, characterized in that, The acetic acid - sodium acetate buffer solution is prepared by the following steps: Weigh anhydrous sodium acetate and dissolve it in distilled water, add acetic acid to adjust the pH of the solution to obtain an acetic acid - sodium acetate buffer solution with a pH of 4.5 - 6.

0.

7. The determination system of octadecylamine in potassium chloride according to claim 1, characterized in that The water - soluble indicator is sodium bromocresol green, potassium bromocresol green, sodium bromophenol blue or potassium bromophenol blue.

8. The determination system of octadecylamine in potassium chloride according to claim 1, wherein, The long-chain alkane is C n H 2n+2 , where n = 7 - 14, and the long-chain alkane is a mixture of one or two or more kinds.

9. The determination system of octadecylamine in potassium chloride according to claim 1, wherein, In the described determination system, the volume ratio of the buffer solution to the water - soluble indicator solution is (5 - 100):

1.

10. The determination system of octadecylamine in potassium chloride according to claim 1, characterized in that, The concentration of the octadecylamine standard solution is 0.5 mg / L - 100 mg / L.

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