Method for measuring content of sodium thiocyanate in milk

Abstract

The invention discloses a method for measuring the content of sodium thiocyanate in milk, which comprises the following steps: firstly, at least carrying out deproteinization treatment on a milk sample to be measured to obtain a pretreated sample; secondly, uniformly mixing the pretreated sample with a ferric salt solution to form a mixed sample, fully reacting the mixed sample in a static magnetic field, and then detecting the light absorption value of the obtained reaction mixture at the wavelength of 455 nm in the static magnetic field; and then calculating the content of sodium thiocyanate in the milk sample to be detected according to the light absorption value and a standard curve formula. Compared with the prior art, the detection method provided by the invention has the advantages of high precision, sensitivity and accuracy, simplicity in operation, good safety and the like.

Description

Technical Field

[0001] The present application relates to a method for detecting milk, and in particular to a method for determining the content of sodium thiocyanate in milk by combining a magnetic field with ultraviolet spectrophotometry. Background Art

[0002] Milk and dairy products are important sources of high-quality protein in the diet, especially liquid milk represented by cow's milk, which is widely loved by consumers because it is rich in nutrients such as protein, vitamins and minerals, and has special functions such as promoting digestion, promoting absorption and anti-aging, and has become an indispensable part of human diet. However, with the rapid development of the dairy industry, the quality and safety of dairy products have become increasingly prominent and have attracted much attention.

[0003] Sodium thiocyanate is a common chemical raw material, which is widely used in the fields of chemistry, medicine, printing and dyeing. In recent years, some lawless persons have added sodium thiocyanate to fresh milk to inhibit the reproduction of microorganisms in order to save sterilization costs. However, sodium thiocyanate is toxic. Large amounts of intake into the human body can cause acute toxic effects such as nervous system passivation, digestive system disorders, kidney damage, blood cell lesions, and skin tissue damage. Therefore, the sodium thiocyanate content in milk must be tested in a targeted manner to avoid excessive sodium thiocyanate content affecting human health.

[0004] Currently, the commonly used methods for detecting sodium thiocyanate content in milk mainly include spectrophotometry, ion chromatography, high performance liquid chromatography and Raman spectroscopy. Among them, the sensitivity and accuracy of chromatography and spectroscopy are relatively high, but there are generally problems such as narrow linear range of detection, insufficient flexibility, low throughput, high instrument and equipment costs and high detection threshold. In contrast, ultraviolet spectrophotometry has the advantages of simple operation, low cost and wide linear range, but the sensitivity, accuracy and stability of detection still need to be improved. Summary of the invention

[0005] The main purpose of this application is to provide a method for determining the content of sodium thiocyanate in milk to overcome the deficiencies in the prior art.

[0006] In order to achieve the aforementioned invention objectives, the technical solutions adopted in this application include: Some embodiments of the present application provide a method for determining the content of sodium thiocyanate in milk, which comprises the following steps: S1. Deproteinize at least the milk sample to be tested to obtain a pre-treated sample; S2, uniformly mixing the pretreated sample with the iron salt solution to form a mixed sample, and then allowing the mixed sample to fully react in a static magnetic field, and then detecting the absorbance value A of the obtained reaction mixture (also referred to as "test reaction solution") at a wavelength of 455 nm in the static magnetic field, wherein the magnetic field strength of the static magnetic field is 0.5-0.8 T; S3, calculate the sodium thiocyanate content Y in the milk sample to be tested according to the absorbance value A and the following standard curve formula, Y=35.216A+C Among them, the value of C is 0.057~0.331.

[0007] In one embodiment, step S1 specifically includes: fully mixing the milk sample to be tested with the deproteinization solvent in a volume ratio of 1:1-4:1, and performing the deproteinization treatment at 35-55°C, then centrifuging the obtained mixed system, collecting the clarified liquid, and adjusting the pH value of the clarified liquid to 3-6 to obtain the pretreated sample.

[0008] In one embodiment, the deproteinization solvent includes but is not limited to a combination of one or more of trichloroacetic acid solution, acetonitrile, and acetone. Further, the concentration of the trichloroacetic acid solution is 10 wt% to 30 wt%.

[0009] In one embodiment, the deproteinization treatment time is 10 to 30 min.

[0010] In one embodiment, the centrifugal treatment is performed at a centrifugal speed of 8000 rpm or more, preferably 8000-10000 rpm, more preferably 8000-9000 rpm, and the centrifugal time is 20-30 min.

[0011] In some cases, the mixed system may also be filtered to collect the clarified liquid.

[0012] In one embodiment, the pH value of the clarified liquid can be adjusted to 3-6 using hydrochloric acid or a pH buffer solution.

[0013] In one embodiment, the volume ratio of the pretreated sample to the iron salt solution in step S2 is 5:1-20:1, and the concentration of the iron salt solution is 1-4 mg / L.

[0014] In one embodiment, the iron salt solution contains iron salts including but not limited to FeCl 3 , Fe 2 (SO 4 ) 3 、Fe(NO 3 ) 3 A combination of one or more of .

[0015] In one embodiment, when detecting the absorbance value A in step S2, the transmission direction of the ultraviolet light used is perpendicular to the magnetic field direction of the static magnetic field.

[0016] In one embodiment, step S2 is performed in an environment with a temperature of 5-8°C.

[0017] In one embodiment, the reaction time of the reaction is 8 to 12 min.

[0018] In one embodiment, step S2 specifically includes: adding the pretreated sample and the iron salt solution to a quartz cuvette in sequence, and then uniformly mixing them to form the mixed sample, wherein the optical path of the quartz cuvette is 1 cm; Furthermore, when detecting the absorbance value A, the direction of the magnetic lines of force of the static magnetic field vertically penetrates the rough side wall of the quartz cuvette and fully acts on the mixed sample.

[0019] Among them, the pretreated sample and the iron salt solution should be added to the cuvette successively, otherwise it may lead to incomplete complexation reaction and unstable color development.

[0020] Among them, by maintaining the static magnetic field when detecting the absorbance value A, that is, maintaining the same magnetic field environment from reaction to detection, the interaction between the reactants can be enhanced, promoting a more complete coordination reaction and a more stable reaction complex, thereby making the data results during detection more stable and repeatable, otherwise the data during detection is prone to fluctuations.

[0021] In one embodiment, the method further comprises: when detecting the absorbance value A, a blank sample is prepared with distilled water and iron salt solution for reference. The specific operation thereof may include: replacing the pre-treated sample in step S2 with distilled water, measuring the absorbance value of the blank sample at a wavelength of 455 nm, and then subtracting the absorbance value of the blank sample from the measured value of the absorbance value of the reaction solution to be tested at a wavelength of 455 nm to obtain A.

[0022] In one embodiment, the method specifically includes: taking a series of sodium thiocyanate solutions of different concentrations as standard samples, and detecting the absorbance values ​​of the reaction mixtures formed by the reaction of different standard samples with the iron salt solution at a wavelength of 455 nm according to the operations of steps S1 to S2, thereby establishing a relationship curve between the sodium thiocyanate content of each standard sample and the corresponding absorbance value, and then obtaining the standard curve formula. Obviously, the concentration of sodium thiocyanate in each standard sample is known. Moreover, the detection of each standard sample and the corresponding pre-treated sample and blank sample is carried out under the same detection conditions.

[0023] In a more specific embodiment of the present application, a method for determining the content of sodium thiocyanate in milk specifically comprises: (1) Milk containing sodium thiocyanate is used as the milk sample to be tested. After deproteinization, centrifugation or filtration, the resulting clarified liquid is adjusted to acidity (pH = 3-6) to obtain a pretreated sample.

[0024] (2) The pretreated sample and distilled water are placed in cuvettes respectively, and then the iron salt solution is added and mixed thoroughly to form a mixed sample and a blank sample respectively.

[0025] (3) The cuvette containing the mixed sample is placed in a static magnetic field and reacted fully to obtain a reaction solution to be tested, and then the absorbance value A of the reaction solution to be tested at a wavelength of 455 nm is measured in the static magnetic field. During the detection process, a blank sample is also used as a reference.

[0026] (4) Based on A and the standard curve formula Y=35.216A+C, where C is between 0.057 and 0.331, calculate the sodium thiocyanate content Y in the milk.

[0027] Furthermore, the standard curve corresponding to the standard curve formula is a linear curve of sodium thiocyanate content and absorbance value, and the method for establishing the standard curve may include: taking a series of standard solutions with known and different sodium thiocyanate contents, performing detection according to the operations of steps (1) to (3), determining the relationship between the sodium thiocyanate content Y and the sample absorbance value A at the corresponding concentration, and then establishing the standard curve, and then obtaining the standard curve formula. The detection range corresponding to the formula may be 0.01~20.00 mg / L.

[0028] Furthermore, the determination conditions of the standard curve should completely correspond to the determination conditions of the sodium thiocyanate content in milk.

[0029] Compared with the prior art, when determining the sodium thiocyanate content in milk by ultraviolet spectrophotometry, the present application applies a static magnetic field treatment during the combination of sodium thiocyanate and iron salt solution, and uses the magnetic field to change the electron cloud distribution of the ferric thiocyanate complex, so that the range of the positive and negative electron clouds is close to 455 nm, the absorption peak signal is enhanced, and the peak width is narrowed, thereby effectively improving the precision, sensitivity and accuracy of the detection method. At the same time, the detection method of the present application only requires the application of a magnetic field treatment, which also effectively simplifies the operation steps and improves the safety of the detection method. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the principle of determining the sodium thiocyanate content in milk by using a magnetic field combined with ultraviolet spectrophotometry in a typical embodiment of the present application.

[0031] Figure 2It is the ultraviolet absorption spectrum of the ferric thiocyanate complex in the wavelength range of 380-550 nm under the conditions of applying a magnetic field and not applying a magnetic field in Example 1. DETAILED DESCRIPTION

[0032] In view of the many defects of the prior art, the inventors of this case, after long-term research and extensive practice, were very pleasantly surprised to find that when determining the sodium thiocyanate content in the sample to be tested by ultraviolet spectrophotometry, if a static magnetic field treatment is used during the binding process of sodium thiocyanate and trivalent iron ions, not only can the structure of the binding product be made more stable, but also the sensitivity and accuracy of the detection can be improved. The principle is that sodium thiocyanate is composed of sodium ions ( ) and thiocyanate ion ( ). Sodium ions are metal cations, and thiocyanate ions are anions. Ionic bonds are formed between anions and cations through electrostatic interactions. The principle of ultraviolet spectrophotometry for detecting sodium thiocyanate is mainly based on the color reaction between sodium thiocyanate and ferric chloride to generate a blood-red ferric thiocyanate complex, which absorbs monochromatic light of a specific wavelength (455 nm). The content of sodium thiocyanate is determined by measuring its absorbance. In theory, a static magnetic field may affect the electron cloud distribution of ions, thereby changing the radius of the electron cloud, further affecting the distance and interaction force between anions and cations, and thus changing the stability of ionic bonds. For example, if the static magnetic field reduces the radius of cations and increases the radius of anions, the effective distance between anions and cations may be shortened, and the bond energy of ionic bonds increases, thereby enhancing the absorbance of monochromatic light passing through a solution containing an absorbing substance, namely the ion complex, and improving detection sensitivity and accuracy.

[0033] Based on the above unexpected discovery, the applicant was able to propose the technical solution of this application, see Figure 1 As shown, it mainly provides a method for determining the content of sodium thiocyanate in milk by using a magnetic field combined with ultraviolet spectrophotometry, comprising the following steps: S1. Deproteinize, centrifuge or filter the milk sample to be tested in sequence to obtain a pre-treated sample.

[0034] S2, the pre-treated sample and the iron salt solution are uniformly mixed in a container 1 such as a quartz cuvette to form a mixed sample 2, and then the mixed sample is fully reacted in a static magnetic field with an intensity of 0.5~0.8 T, and then the absorbance value A of the obtained reaction solution to be tested at a wavelength of 455 nm is detected in the static magnetic field. The static magnetic field can be formed by a permanent magnet 3, etc., and when detecting the absorbance value, the direction of the magnetic field lines 4 of the static magnetic field vertically penetrates the rough side wall of the cuvette, and the transmission direction of the ultraviolet visible light 6 emitted by the light source 5 vertically penetrates the smooth side wall of the cuvette, that is, perpendicular to the magnetic field direction of the static magnetic field. In the detection process, a blank sample is also made of distilled water and iron salt solution for reference.

[0035] S3, calculate the sodium thiocyanate content Y in the milk sample to be tested according to the absorbance value A and the following standard curve formula, Y=35.216A+C Among them, the value of C is 0.057~0.331.

[0036] The method for obtaining the standard curve formula mainly includes: using a series of sodium thiocyanate solutions of different and known concentrations as standard samples, and detecting the absorbance value of the reaction solution to be tested formed by each standard sample at a wavelength of 455 nm according to the operations of the aforementioned steps S1 to S2, and then establishing a standard curve based on the concentration of sodium thiocyanate in each standard sample and the corresponding absorbance value detected, and finally summarizing the standard curve formula based on the standard curve.

[0037] The method of the present application has the advantages of high detection precision, sensitivity and accuracy, simple operation and good safety.

[0038] The technical solution, its implementation process and principle, etc. will be further explained in conjunction with several embodiments as follows. However, it should be understood that within the scope of this application, the above-mentioned technical features of this application and the technical features specifically described in the following (embodiments) can be combined with each other to form a new or preferred technical solution. Due to space limitations, they will not be described one by one here.

[0039] In the following examples of the present application, unless otherwise specified, the various raw materials, reagents, reaction equipment, testing equipment and methods used can be obtained through commercial purchase and other channels.

[0040] In addition, in the following examples of the present application, the calculation methods of the spike recovery θ (%) and the relative deviation (%) of the detection results of different methods are respectively: Spike recovery θ (%): 10 mL pre-treated sample (sodium thiocyanate concentration is Y 0 ) was added with 0.1 mL of 0.5 g / L sodium thiocyanate standard solution and the spiked concentration Y was calculated. 1 , perform the test according to the operation described in steps S1 to S3, obtain the corresponding absorbance value A, and then calculate the measured value Y of the sodium thiocyanate content of the milk to be tested after adding the spike according to the relationship between A and the standard curve 2 , then the spike recovery θ (%) = (Y 2 -Y 0 ) / Y 1 ×100.

[0041] Reproducibility test: After the reaction was completed, the sodium thiocyanate content of the sample was tested once a day for 5 consecutive days, and the relative standard deviation was calculated.

[0042] Relative deviation of the test results of different methods (%): Let the test result of this implementation method be Y a , the control method test result is Y b , then the relative deviation (%) = (Y a -Y b ) / Y c ×100, where Y c is the average of the two test results.

[0043] Example 1 A method for determining the content of sodium thiocyanate in high-calcium milk comprises the following steps: S1. Take 10 mL of high-calcium milk and 5 mL of 20wt% trichloroacetic acid solution and mix them thoroughly. Let it stand in a 45℃ water bath for 20 min to precipitate the protein. Then centrifuge it at 8000 rpm for 25 min, collect the clarified liquid, and adjust the pH value to 4 with 0.1mol / L HCl solution to obtain the pretreated sample.

[0044] S2, take 3 mL of the pretreated sample and place it in a quartz cuvette with an optical path of 1 cm, add 0.3 mL of 2 mg / LFeCl 3 Solution, mix thoroughly to obtain a mixed sample. At the same time, 3 mL of distilled water was used to replace the pretreated sample and a blank sample was prepared by the same operation.

[0045] S3. Place the mixed sample in an ultraviolet spectrophotometer equipped with a magnetic field processing chamber, set the ambient temperature in the chamber to 6°C, the magnetic field type to a static magnetic field, the magnetic field intensity to 0.6 T, the direction of the magnetic field lines to be perpendicular to the rough side wall of the cuvette, and allow to react for 10 min to obtain a reaction solution to be tested. Continue to apply the static magnetic field, and use a blank sample as a reference to measure the absorbance value A of the reaction solution to be tested at a wavelength of 455 nm.

[0046] Standard curve determination: Take a series of sodium thiocyanate solutions with concentrations of 0, 0.1, 0.5, 1, 2, 4, 6, 8, 10, 12, 14, 16, and 18 mg / L as standard samples, and determine the absorbance values ​​of these standard samples at a wavelength of 455 nm according to the operations of steps S1 to S3. By collecting the obtained data and building a model, the relationship between the sodium thiocyanate content Y in the standard sample and the absorbance value A is obtained, Y=35.216A+0.136, and the detection range is 0.136~17.744 mg / L.

[0047] For the high-calcium milk to be tested with unknown sodium thiocyanate content, the operation described in steps S1 to S3 is performed to obtain the corresponding absorbance value A, and then the sodium thiocyanate content in the high-calcium milk to be tested is calculated based on A and the relationship between the above standard curve.

[0048] Figure 2 The results show that when the standard sample with a concentration of 14 mg / L is tested under the conditions of applying and not applying the magnetic field, the sodium thiocyanate and FeCl 3 Ultraviolet absorption spectrum of the ferric thiocyanate complex formed by the reaction in the wavelength range of 380~550 nm.

[0049] The method of this embodiment and the first method ion chromatography (control method) in SN / T 3927-2014 were used to detect the sodium thiocyanate content in 8 portions of high-calcium milk. As shown in Table 1, the relative standard deviation of the detection results of the method of this embodiment was always lower than 1.82%, the spike recovery rate fluctuated between 95.32% and 98.60%, and the relative standard deviation of the detection results for five consecutive days was always below 1.88%, indicating that the method has high precision and reproducibility. In addition, compared with the method described in SN / T 3927-2014, the relative deviation of the detection results was always less than ±2%, and the accuracy was high.

[0050] Table 1 Test results of sodium thiocyanate content in 8 portions of high calcium milk by the method of Example 1

[0051] Example 2 A method for determining the content of sodium thiocyanate in breakfast milk comprises the following steps: S1. Take 10 mL of breakfast milk and 10 mL of acetonitrile and mix them thoroughly. Place the mixture in a 35 °C water bath for 10 min to precipitate the protein. Then centrifuge it at 8500 rpm for 20 min, collect the clarified liquid, and adjust the pH value to 3 with 0.1 mol / L HCl solution to obtain the pretreated sample.

[0052] S2, take 3 mL of the pretreated sample into a quartz cuvette with an optical path of 1 cm, add 0.6 mL of 1 mg / LFeCl 3 Solution, mix thoroughly to obtain a mixed sample. At the same time, 3 mL of distilled water was used to replace the pretreated sample and a blank sample was prepared by the same operation.

[0053] S3. Place the mixed sample in an ultraviolet spectrophotometer equipped with a magnetic field treatment chamber, set the ambient temperature in the chamber to 5°C, the magnetic field type to a static magnetic field, the magnetic field intensity to 0.5 T, the direction of the magnetic field lines to be perpendicular to the rough side wall of the cuvette, allow to react for 12 min to obtain a reaction solution to be tested, and continue to apply static magnetic field treatment. Using a blank sample as a reference, determine the absorbance value A of the reaction solution to be tested at a wavelength of 455 nm.

[0054] Standard curve determination: Take a series of sodium thiocyanate solutions with concentrations of 0, 0.1, 0.5, 1, 2, 4, 6, 8, 10, 12, 14, 16, and 18 mg / L as standard samples, and determine the absorbance values ​​of these standard samples at a wavelength of 455 nm according to the operations described in steps S1 to S3. By collecting the obtained data and building a model, the relationship between the sodium thiocyanate content Y in the standard sample and the absorbance value A is obtained, which is Y=35.216A+0.318, and the detection range is 0.318~13.926 mg / L.

[0055] For breakfast milk to be tested with unknown sodium thiocyanate content, the steps described in steps S1 to S3 are followed to perform detection to obtain its corresponding absorbance value A, and then the sodium thiocyanate content in the breakfast milk to be tested is calculated based on the relationship between A and the above standard curve.

[0056] The sodium thiocyanate content in 8 breakfast milks was tested by the method of this embodiment and the first method ion chromatography (control method) in SN / T 3927-2014, respectively. As shown in Table 2, the relative standard deviation of the test results of the method of this embodiment is always lower than 2.53%, the spike recovery rate fluctuates between 94.72% and 97.30%, and the relative standard deviation of the test results for five consecutive days is always below 2.36%, indicating that the method has high precision and reproducibility. In addition, compared with the method described in SN / T 3927-2014, the relative deviation of the test results is always less than ±3%, and the accuracy is high.

[0057] Table 2 Detection results of sodium thiocyanate content in 8 breakfast milks by the method of Example 2

[0058] Example 3 A method for determining the content of sodium thiocyanate in skim milk comprises the following steps: S1. Take 20 mL of skim milk and 5 mL of 30 wt% trichloroacetic acid solution and mix them thoroughly. Place them in a 55 °C water bath for 30 min to precipitate the protein. Then centrifuge them at 9000 rpm for 30 min, collect the clarified liquid, and adjust the pH value to 6 with phosphate buffer solution to obtain the pretreated sample.

[0059] S2, take 3 mL of the pretreated sample into a quartz cuvette with an optical path of 1 cm, add 0.15 mL of 4 mg / L Fe(NO 3 ) 3 Solution, mix thoroughly to obtain a mixed sample. At the same time, 3 mL of distilled water was used to replace the pretreated sample and a blank sample was prepared by the same operation.

[0060] S3. Place the mixed sample in an ultraviolet spectrophotometer equipped with a magnetic field treatment chamber, set the ambient temperature in the chamber to 8°C, the magnetic field type to a static magnetic field, the magnetic field intensity to 0.8 T, the direction of the magnetic field lines to be perpendicular to the rough side wall of the cuvette, allow to react for 8 min, and continue to apply the static magnetic field treatment. Using the blank sample as a reference, determine the absorbance value A of the reaction solution to be tested at a wavelength of 455 nm.

[0061] Standard curve determination: Take a series of sodium thiocyanate solutions with concentrations of 0, 0.1, 0.5, 1, 2, 4, 6, 8, 10, 12, 14, 16, and 18 mg / L as standard samples, and determine the absorbance values ​​of these standard samples at a wavelength of 455 nm according to the operations described in steps S1 to S3. By collecting the obtained data and building a model, the relationship between the sodium thiocyanate content Y in the standard sample and the absorbance value A is obtained, which is Y=35.216A+0.086, and the detection range is 0.086~17.046 mg / L.

[0062] For the skim milk to be tested with unknown sodium thiocyanate content, the operation described in steps S1 to S3 is performed to obtain the corresponding absorbance value A, and then the sodium thiocyanate content in the skim milk to be tested is calculated based on A and the relationship between the above standard curve.

[0063] The method of this embodiment and the first method ion chromatography (control method) in SN / T 3927-2014 were used to detect the sodium thiocyanate content in 10 portions of skim milk. As shown in Table 3, the relative standard deviation of the detection results of the method of this embodiment was always lower than 2.56%, the spike recovery rate fluctuated between 93.55% and 97.18%, and the relative standard deviation of the detection results for five consecutive days was always below 2.52%, indicating that the method has high precision and reproducibility. In addition, compared with the method described in SN / T 3927-2014, the relative deviation of the detection results was always less than ±3%, and the accuracy was high.

[0064] Table 3 Test results of sodium thiocyanate content in 10 portions of skim milk by the method of Example 3

[0065] Comparative Example 1 A method for determining the content of sodium thiocyanate in high-calcium milk, which is basically the same as the method in Example 1, except that the magnetic field strength of the static magnetic field in step S3 is 0.4 T.

[0066] Standard curve determination: Take a series of sodium thiocyanate solutions with concentrations of 0, 0.1, 0.5, 1, 2, 4, 6, 8, 10, 12, 14, 16, and 18 mg / L as standard samples, and determine the absorbance values ​​of these standard samples at a wavelength of 455 nm according to the steps described in this comparative example. By collecting the obtained data and modeling, the relationship between the sodium thiocyanate content Y in the standard sample and the absorbance value A is obtained, Y=26.269A+0.238, and the detection range is 0.238~15.525 mg / L.

[0067] For the high-calcium milk to be tested with unknown sodium thiocyanate content, the detection is carried out according to the steps described in this comparative example to obtain its corresponding absorbance value A, and then the sodium thiocyanate content in the high-calcium milk to be tested is calculated based on A and the relationship between the above standard curve.

[0068] The sodium thiocyanate content in 8 portions of high-calcium milk (the same as Example 1) was detected by the method of this comparative example and the first method ion chromatography (control method) in SN / T 3927-2014, respectively. As shown in Table 4, the relative standard deviation of the detection results of the comparative example method varied in the range of 1.74% to 4.71%, the spiked recovery rate fluctuated between 91.53% and 95.24%, and the relative standard deviation of the detection results for five consecutive days varied in the range of 2.14% to 4.78%, indicating that the precision and reproducibility of the method were poor. In addition, compared with the detection results of the method described in SN / T 3927-2014, the relative deviation was large, up to -4.64%, indicating that the accuracy of the detection results was insufficient, which may be related to the low applied magnetic field intensity, resulting in poor stability of the formed ferric thiocyanate complex and weakened absorption signal at a wavelength of 455 nm.

[0069] Table 4 Test results of sodium thiocyanate content in 8 portions of high calcium milk by comparative example 1

[0070] Comparative Example 2 A method for determining the content of sodium thiocyanate in high-calcium milk is substantially the same as the method in Example 1, except that the magnetic field strength of the static magnetic field in step S3 is 1.0 T.

[0071] Standard curve determination: Take a series of sodium thiocyanate solutions with concentrations of 0, 0.1, 0.5, 1, 2, 4, 6, 8, 10, 12, 14, 16, and 18 mg / L as standard samples, and determine the absorbance values ​​of these standard samples at a wavelength of 455 nm according to the steps described in this comparative example. By collecting the obtained data and modeling, the relationship between the sodium thiocyanate content Y and the absorbance value A in the standard sample is obtained, Y=31.573A+0.438, and the detection range is 0.438~15.225 mg / L.

[0072] For the high-calcium milk to be tested with unknown sodium thiocyanate content, the detection is carried out according to the steps described in this comparative example to obtain its corresponding absorbance value A, and then the sodium thiocyanate content in the high-calcium milk to be tested is calculated based on A and the relationship between the above standard curve.

[0073] The sodium thiocyanate content in 8 portions of high-calcium milk (the same as Example 1) was detected by the method of this comparative example and the first method ion chromatography (control method) in SN / T 3927-2014, respectively. As shown in Table 5, the relative standard deviation of the detection results of the comparative example method varied in the range of 2.74% to 4.53%, the spiked recovery rate fluctuated between 90.24% and 94.13%, and the relative standard deviation of the detection results for five consecutive days varied in the range of 2.53% to 4.27%, indicating that the precision and reproducibility of the method were poor. In addition, compared with the detection results of the method described in SN / T 3927-2014, the relative deviation was large, up to 4.94%, indicating that the accuracy of the detection results was insufficient, which may be related to the large applied magnetic field strength, resulting in the deviation of the positive and negative symmetry centers of the electron cloud of the ferric thiocyanate complex.

[0074] Table 5 Test results of sodium thiocyanate content in 8 portions of high calcium milk by comparative example 2

[0075] Comparative Example 3 A method for determining the content of sodium thiocyanate in high-calcium milk is substantially the same as the method in Example 1, except that the direction of the static magnetic field in step S3 is perpendicular to the smooth side wall of the cuvette.

[0076] Standard curve determination: Take a series of sodium thiocyanate solutions with concentrations of 0, 0.1, 0.5, 1, 2, 4, 6, 8, 10, 12, 14, 16, and 18 mg / L as standard samples, and determine the absorbance values ​​of these standard samples at a wavelength of 455 nm according to the steps described in this comparative example. By collecting the obtained data and modeling, the relationship between the sodium thiocyanate content Y in the standard sample and the absorbance value A is obtained, Y=36.715A+0.892, and the detection range is 0.892~15.813 mg / L.

[0077] For the high-calcium milk to be tested with unknown sodium thiocyanate content, the detection is carried out according to the steps described in this comparative example to obtain its corresponding absorbance value A, and then the sodium thiocyanate content in the high-calcium milk to be tested is calculated based on A and the relationship between the above standard curve.

[0078] The sodium thiocyanate content in 8 portions of high-calcium milk (the same as Example 1) was detected by the method of this comparative example and the first method ion chromatography (control method) in SN / T 3927-2014, respectively. As shown in Table 6, the relative standard deviation of the detection results of the comparative example method varied in the range of 3.19% to 4.94%, the spiked recovery rate fluctuated between 88.39% and 92.20%, and the relative standard deviation of the detection results for five consecutive days varied in the range of 2.50% to 4.20%, indicating that the precision and reproducibility of the method were poor. In addition, compared with the detection results of the method described in SN / T 3927-2014, the relative deviation was large, up to 7.87%, indicating that the accuracy of the detection results was insufficient. The magnetic field acted perpendicularly on the smooth side wall and parallel to the direction of the light source. The electron cloud of the ferric thiocyanate complex agglomerated in the direction of the light source, affecting the color development.

[0079] Table 6 Test results of sodium thiocyanate content in 8 portions of high calcium milk by comparative example 3

[0080] Comparative Example 4 A method for determining the content of sodium thiocyanate in high-calcium milk is substantially the same as the method in Example 1, except that in step S3, after the reaction is completed, the magnetic field is removed and the absorbance value A is detected.

[0081] Standard curve determination: Take a series of sodium thiocyanate solutions with concentrations of 0, 0.1, 0.5, 1, 2, 4, 6, 8, 10, 12, 14, 16, and 18 mg / L as standard samples, and determine the absorbance values ​​of these standard samples at a wavelength of 455 nm according to the steps described in this comparative example. By collecting the obtained data and modeling, the relationship between the sodium thiocyanate content Y in the standard sample and the absorbance value A is obtained, Y=25.016A+0.413, and the detection range is 0.413~14.924 mg / L.

[0082] For the high-calcium milk to be tested with unknown sodium thiocyanate content, the detection is carried out according to the steps described in this comparative example to obtain its corresponding absorbance value A, and then the sodium thiocyanate content in the high-calcium milk to be tested is calculated based on A and the relationship between the above standard curve.

[0083] The sodium thiocyanate content in 8 portions of high-calcium milk (the same as Example 1) was detected by the method of this comparative example and the first method ion chromatography (control method) in SN / T 3927-2014, respectively. As shown in Table 7, the relative standard deviation of the detection results of the comparative example method varied in the range of 2.66% to 4.39%, the spiked recovery rate fluctuated between 88.43% and 92.24%, and the relative standard deviation of the detection results for five consecutive days varied in the range of 2% to 5%, indicating that the precision and reproducibility of the method were poor. In addition, compared with the detection results of the method described in SN / T 3927-2014, the relative deviation was large, up to -4.91%, indicating that no magnetic field was applied during the detection process, the enhancement effect of the ferric thiocyanate complex decreased or even disappeared, the complex structure was unstable, the color development effect was affected, and the detection accuracy decreased.

[0084] Table 7 Test results of sodium thiocyanate content in 8 portions of high calcium milk by comparative example 4

[0085] The above-mentioned embodiments of the present application use sodium thiocyanate in milk as the detection object, and enhance the precision, sensitivity and accuracy of ultraviolet spectrophotometry for detecting the content of sodium thiocyanate by applying a magnetic field. Specifically, by applying a static magnetic field treatment during the combination of sodium thiocyanate and iron ions, the magnetic field is used to change the electron cloud distribution of the iron thiocyanate complex, so that the range of the positive and negative electron clouds is close to 455 nm, the absorption peak signal is enhanced, and the peak width is narrowed, which effectively improves the precision, sensitivity and accuracy of the detection method. In addition, the method provided by the above-mentioned embodiments of the present application only needs to apply a magnetic field treatment, and the process is simple, the operation is convenient, and the safety is high.

[0086] The above is a detailed description of the present application in combination with the embodiments, but the implementation methods of the present application are not limited to the above embodiments, and any other changes, replacements, combination simplifications, etc. made under the core guiding idea of ​​the present application are included in the protection scope of the patent of this application.

Claims

1. A method for determining the content of sodium thiocyanate in milk, characterized in that: The steps include: S1. Deproteinize at least the milk sample to be tested to obtain a pre-treated sample; S2, uniformly mixing the pretreated sample with the iron salt solution to form a mixed sample, and then allowing the mixed sample to fully react in a static magnetic field, and then detecting the absorbance value A of the obtained reaction mixture at a wavelength of 455 nm in the static magnetic field, wherein the magnetic field strength of the static magnetic field is 0.5-0.8 T; S3, calculate the sodium thiocyanate content Y in the milk sample to be tested according to the absorbance value A and the following standard curve formula, Y=35.216A+C Among them, the value of C is 0.057~0.

331.

2. The method according to claim 1, characterized in that Step S1 specifically includes: fully mixing the milk sample to be tested with the deproteinization solvent in a volume ratio of 1:1-4:1, and performing the deproteinization treatment at 35-55°C, then centrifuging the obtained mixed system, collecting the clarified liquid, and adjusting the pH value of the clarified liquid to 3-6 to obtain the pretreated sample.

3. The method according to claim 2, characterized in that: The deproteinization solvent includes a combination of one or more of trichloroacetic acid solution, acetonitrile, and acetone, and the concentration of the trichloroacetic acid solution is 10wt% to 30wt%; And / or, the deproteinization treatment time is 10 to 30 min.

4. The method according to claim 2, characterized in that: The centrifugal treatment is performed at a centrifugal speed of 8000 rpm or more and a centrifugal time of 20 to 30 min.

5. The method according to claim 1, characterized in that: In step S2, the volume ratio of the pretreated sample to the iron salt solution is 5:1-20:1, and the concentration of the iron salt solution is 1-4 mg / L; And / or, the iron salt contained in the iron salt solution includes one or more combinations of FeCl3, Fe2(SO4)3, and Fe(NO3)3.

6. The method according to claim 1, characterized in that: Step S2 is performed in an environment with a temperature of 5-8°C; and / or, the reaction time of the reaction is 8-12 min.

7. The method according to claim 1, characterized in that: When detecting the absorbance value A in step S2, the transmission direction of the ultraviolet light used is perpendicular to the magnetic field direction of the static magnetic field.

8. The method according to claim 7, characterized in that Step S2 specifically includes: adding the pretreated sample and the iron salt solution into a quartz cuvette in sequence, and then uniformly mixing them to form the mixed sample, wherein the optical path of the quartz cuvette is 1 cm; Furthermore, when detecting the absorbance value A, the direction of the magnetic lines of force of the static magnetic field vertically penetrates the rough side wall of the quartz cuvette and fully acts on the mixed sample.

9. The method according to any one of claims 1 to 8, characterized in that Step S2 also includes: when detecting the absorbance value A, a blank sample is prepared with distilled water and iron salt solution for reference.

10. The method according to claim 1, characterized in that Specifically, the method comprises: taking a series of sodium thiocyanate solutions of different concentrations as standard samples, and detecting the absorbance values ​​of the reaction mixtures formed by the reaction of different standard samples with the iron salt solution at a wavelength of 455 nm according to the operations of steps S1 to S2, thereby establishing a relationship curve between the sodium thiocyanate content of each standard sample and the corresponding absorbance value, and then obtaining the standard curve formula.

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