Method for determining iodine content in formula food for special medical purpose

Abstract

The invention relates to the technical field of food detection, in particular to a method for determining the iodine content in formula food for special medical purposes. The determination method comprises the following steps: (1) weighing potassium iodide, and adding water for dissolving to obtain a reference substance working solution; (2) adding water into a test sample to obtain a sample suspension, and performing alkali ashing treatment to obtain a sample solution; (3) adding a sulfuric acid solution and a reagent adopted for alkali ashing treatment into the reference substance working solution, and respectively performing derivatization treatment and organic solvent extraction on the reference substance working solution and the sample solution to obtain a reference substance solution and a test solution; (4) testing by adopting a gas chromatographic method, and calculating the iodine content; reagents adopted in the alkali ashing treatment are a potassium hydroxide solution, a potassium nitrate solution and a potassium permanganate solution (or manganese dioxide); the derivatization treatment comprises the steps of adding a sodium sulfite solution, standing, and adding a ketone reagent and a hydrogen peroxide solution to carry out a derivatization reaction. The method has the advantages of being low in cost, high in safety and high in accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of food detection, and specifically relates to a method for determining the iodine content in formula foods for special medical purposes. Background Art

[0002] Formula foods for special medical purposes, abbreviated as FSMPs, are formula foods specially processed and prepared to meet the special nutritional needs of people with eating restrictions, disorders of digestion and absorption, metabolic disorders, or specific disease states for nutrients or diets. Iodine is one of the essential trace elements for the human body and is often added as a nutrient to FSMPs. Excessive intake of iodine can lead to thyroid dysfunction and affect human health. Therefore, during the formula design process of FSMPs, it is necessary to adjust the product according to the physiological characteristics of users to control the iodine content to meet the nutritional needs of users. Thus, it is particularly important to use a suitable determination method to measure the iodine content in FSMPs for the development and quality control of FSMPs.

[0003] Currently, the detection of iodine content in FSMPs mainly adopts the first method in GB 5009.267-2020 "National Food Safety Standard - Determination of Iodine in Foods" - inductively coupled plasma mass spectrometry (ICP-MS method). The main steps include: weighing a homogenized sample, adding an extraction solution, vortexing until the sample is evenly dispersed, placing it in a constant temperature drying oven or a water bath shaker for extraction, cooling and then making up the volume, taking the supernatant after high-speed centrifugation and filtering. It is measured using an inductively coupled plasma mass spectrometer. Potassium iodide is used as a standard product and an internal standard element (one or several of tellurium, rhodium, indium, and rhenium) is added, and the iodine content in the sample is determined by the standard curve method. The main advantages of this method are that the sample pretreatment process is simple, the determination is fast, and the sensitivity is high. However, the penetration rate of inductively coupled plasma mass spectrometers is relatively low, the use and maintenance costs are relatively high, and tetramethylammonium hydroxide used in the testing process is highly toxic. These factors limit the application of this method to a certain extent.

[0004] Chinese Patent Publication No. CN104215706A discloses a gas chromatography analysis method for determining the iodine content in foods. The specific steps are as follows: (1) Sample ashing: Weigh 0.2 g - 0.5 g of the sample and place it in a porcelain crucible, add 1 ml of 10% potassium carbonate solution and 1 ml of 10% zinc sulfate solution for wetting, mix evenly, and heat until no smoke is generated; transfer it to a muffle furnace for ashing and cool down; (2) Sample derivatization: Dissolve the ashed product with 10 ml of 0.15 mol / L sulfuric acid aqueous solution, then add 1 ml of butanone and 2 ml of 3.5% H2O2, vortex and mix evenly, and let it stand; (3) Sample extraction: Add n-hexane for extraction, combine the organic phases, wash with distilled water until neutral, let it stand, and take the supernatant as the test solution; (4) Sample injection and detection: Use a gas chromatograph to determine the iodine content in the test solution.

[0005] The above method avoids the use of inductively coupled plasma mass spectrometry and toxic solvents. However, when the above method is used in the detection of special medical foods, there are still carbon particle residues after dissolving with sulfuric acid aqueous solution, indicating incomplete ashing. And there is matrix interference in the dissolved residue, and iodine loss occurs during the ashing process, resulting in low accuracy of the detection results.

[0006] Therefore, it is very necessary to develop a method for determining the iodine content in special medical purpose formula foods that can solve the above technical problems. Summary of the Invention

[0007] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for determining the iodine content in special medical purpose formula foods with lower cost, higher safety and higher accuracy.

[0008] The present invention is realized through the following technical solutions: The present invention provides a method for determining the iodine content in special medical purpose formula foods, including the following steps: (1) Prepare the reference solution working solution: Weigh potassium iodide, dissolve it in water to obtain the reference solution working solution; (2) Alkaline ashing treatment: Add water to the test sample to obtain a sample suspension, and perform alkaline ashing treatment to obtain a sample solution; (3) Derivatization treatment: Add sulfuric acid solution and the reagent used in the alkaline ashing treatment in step (2) to the reference solution working solution, and then perform derivatization treatment and organic solvent extraction on the reference solution working solution and the sample solution respectively to obtain a reference solution and a test solution; (4) Testing: Inject the reference solution and the test solution respectively, and use gas chromatography for testing to calculate the iodine content; The reagent used in the alkaline ashing treatment is potassium hydroxide solution, potassium nitrate solution and manganese-containing reagent, and the manganese-containing reagent is at least one of potassium permanganate solution and manganese dioxide; The derivatization treatment includes adding sodium sulfite solution, standing, and adding a ketone reagent and hydrogen peroxide solution for derivatization reaction.

[0009] In the alkaline ashing treatment process of the present invention, potassium hydroxide solution, potassium nitrate solution and potassium permanganate solution, or potassium hydroxide solution, potassium nitrate solution and manganese dioxide are used. Potassium hydroxide is used as a fixative, potassium nitrate is used as an oxidant, and the role of potassium permanganate or manganese dioxide is to accelerate the ashing process and avoid iodine loss during the ashing process. After the ashing residue is dissolved and reduced by sodium sulfite, a clear and colorless solution is obtained, which can completely eliminate the interference of the organic matrix, and at the same time, there is no iodine loss during the ashing process.

[0010] In the ashing reagent of the present invention, potassium permanganate is immediately reduced to tetravalent manganese when added to the sample and loses its oxidizing property. Therefore, its main function is not as an oxidant, but to catalytically accelerate the ashing process and prevent the volatilization of iodine during the ashing process.

[0011] As an embodiment of the present invention, the alkali ashing treatment in step (2) is carried out in a nickel crucible. Compared with crucibles made of other materials such as quartz crucibles and porcelain crucibles, the nickel crucible can improve the iodine recovery rate.

[0012] As an embodiment of the present invention, the ketone reagent includes 3-pentanone. Compared with other ketone reagents, 3-pentanone can improve the response value, indicating that 3-pentanone has higher sensitivity.

[0013] As an embodiment of the present invention, in step (4), the gas chromatography is tested using a 35%-trifluoropropyl-methyl polysiloxane stationary phase capillary column.

[0014] As an embodiment of the present invention, the concentration of the potassium hydroxide solution is 29%, and the volume-mass ratio with the test sample is 3-5 ml / g.

[0015] As an embodiment of the present invention, the concentration of the potassium nitrate solution is 20%, and the volume-mass ratio with the test sample is 3-5 ml / g.

[0016] As an embodiment of the present invention, the concentration of the potassium permanganate solution is 1%, and the volume-mass ratio with the test sample is 0.6-0.9 ml / g, and the mass ratio of manganese dioxide to the test sample is 0.003-0.005 g / g.

[0017] As an embodiment of the present invention, after adding the potassium hydroxide solution, potassium nitrate solution and manganese-containing reagent to the alkali ashing treatment, the water is evaporated to dryness, the temperature is raised to 280 °C, maintained for 40-60 min, then heated to 600 °C and kept for 40-80 min, and water is added to dissolve the residue to obtain a sample solution.

[0018] As an embodiment of the present invention, during the derivatization treatment process, the concentration of the sodium sulfite solution is 3%, the standing time is 60-90 min, and the concentration of the hydrogen peroxide solution is 30%.

[0019] As an embodiment of the present invention, the reaction time of the derivatization reaction is 20-60 min, and the organic solvent is n-hexane.

[0020] As an embodiment of the present invention, the chromatographic conditions of the gas chromatography method in step (4) include: split ratio 10:1; carrier gas flow rate 1 ml / min; initial column temperature 55 °C, held for 5 min, heated to 110 °C at a rate of 10 °C / min and then heated to 280 °C at a rate of 70 °C / min and held for 5 min.

[0021] As an embodiment of the present invention, the chromatographic conditions of the gas chromatography method in step (4) include: injection port temperature 260 °C, ECD detector temperature 300 °C, injection volume 1 μl.

[0022] The special medical purpose formula food (hereinafter referred to as special medical food) of the present invention usually needs to add a variety of nutritional compounding agents. For the needs of extending the shelf life and stabilizing the product quality, some special processes are used for processing (for example, nutrients such as oils and fats will be encapsulated with microcapsules). Inevitably, some factors interfering with the iodine content determination are introduced during these processing processes. This situation makes the iodine content determination method applicable to general foods ineffective when applied to special medical foods.

[0023] The present invention provides a detection method for determining iodine content in special medical foods, which is safe to operate, low in detection cost, strong in popularization and application, and high in sensitivity. The present invention has tested the effects of various iodine content determination methods applied to special medical foods. The alkali ashing-gas chromatography method has higher safety and lower detection cost. The present invention has made some improvements on the basis of the existing technology, including but not limited to the selection of alkali ashing reagents to be applicable to the detection of special medical foods. Compared with inductively coupled plasma mass spectrometry (ICP-MS method), the method of the present invention only uses conventional analytical instruments in the experimental process, does not use highly toxic reagents, and has the same sensitivity as the ICP-MS method, and has the advantages of low cost, strong popularization and application, and safe operation.

[0024] The beneficial effects of the present invention are: In the ashing process of the present invention, potassium nitrate and manganese-containing reagents are added, and potassium hydroxide is used as a fixing agent, which can completely ash the sample. After the ashing residue is dissolved and reduced by sodium sulfite, a clear and colorless solution is obtained, which can completely eliminate the interference of organic matrix, and at the same time there is no loss of iodine during the ashing process.

[0025] The present invention uses 3-pentanone as a derivatizing reagent, and the sensitivity is doubled compared with using butanone in the existing method.

[0026] The present invention avoids the use of highly toxic reagents, and the operation process is safer.

[0027] The present invention only needs to use conventional analytical instruments in the laboratory, has lower detection cost, and is stronger in popularization and application. Description of the Drawings

[0028] Figure 1 It is the chromatogram of the reference solution for Example 1.

[0029] Figure 2 It is the chromatogram of the test solution for Example 1.

[0030] Figure 3 It is the comparison between the solution obtained by adding sulfuric acid for dissolution and then adding sodium sulfite for reduction after the ashing of the special medical purpose food in Example 1 and the solution obtained by adding sulfuric acid for dissolution after the ashing of the special medical purpose food in Comparative Example 1. Detailed implementation manners

[0031] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description progresses. However, these embodiments are merely exemplary and do not constitute any limitation to the scope of the present invention. Those skilled in the art should understand that without departing from the spirit and scope of the present invention, modifications or substitutions can be made to the details and forms of the technical solutions of the present invention, but such modifications and substitutions all fall within the protection scope of the present invention.

[0032] The special medical purpose formula food adopted in each embodiment of the present invention is Jiangzhong Chuyuan Special Medical Purpose Total Nutrition Formula Food.

[0033] Example 1 A method for determining the iodine content in a special medical purpose formula food, comprising the following steps: (1) Preparation of the reference working solution: Weigh accurately about 13 mg of potassium iodide (previously dried in a silica gel desiccator for 24 hours), dissolve it in water and make up the volume to 100 ml and shake well. Take 1 ml and make up the volume to 100 ml with water, and shake well to prepare the reference working solution.

[0034] (2) Preparation of reagents: ① 29% potassium hydroxide (w / w) solution: Weigh 40 g of potassium hydroxide (AR), dissolve it in 100 ml of water, and obtain it after cooling; ② 20% potassium nitrate (w / w) solution: Weigh 25 g of potassium nitrate (AR), dissolve it in 100 ml of water, and obtain it after restoring to room temperature; ③ 1% potassium permanganate (w / v) solution: Weigh 0.1 g of potassium permanganate (AR), dissolve it in 10 ml of water, and prepare it immediately before use; ④ (5 + 95) sulfuric acid solution: Slowly add 50 ml of sulfuric acid to 950 ml of water, stir while adding, and obtain it after dissolution and cooling; ⑤ 3% sodium sulfite (w / v) solution: Dissolve 0.3 g of sodium sulfite in 10 ml of water, and prepare it immediately before use.

[0035] (3)Alkaline ashing: Weigh accurately about 5 g of the powder of the test sample (formula food for special medical purposes), place it in a 50-ml volumetric flask, add 15 ml of warm water at about 40 °C, sonicate for 30 min, cool, dilute with water to the mark, shake well to obtain a sample suspension. Take 5 ml of the sample suspension and place it in a 50-ml nickel crucible. Add 2 ml of 29% potassium hydroxide solution, 2 ml of 20% potassium nitrate solution, and 0.3 ml of 1% potassium permanganate solution. Gently shake and mix well, place it in an oven at 180 °C for 2 hours to evaporate the water to dryness. Cover the crucible lid and raise the temperature to 280 °C, maintain for 40 min. After taking it out, remove the crucible lid and place it in a muffle furnace and heat to 600 °C and keep for 1 h. After the ashing is completed, take out the crucible and cool it to room temperature. Add 6 ml of water to dissolve the residue and transfer it to a 50-ml screw-cap test tube. Wash it twice with 20 ml of (5 + 95) sulfuric acid solution and transfer it to the same screw-cap test tube to obtain the sample solution.

[0036] (4)Derivatization: Take 0.1 ml, 0.3 ml, 0.5 ml, 1 ml, and 1.5 ml of the reference solution working solution in 50-ml screw-cap test tubes respectively, add 1.6 ml, 1.4 ml, 1.2 ml, 0.7 ml, and 0.2 ml of water respectively, add 2 ml of 29% potassium hydroxide solution, 2 ml of 20% potassium nitrate solution, 0.3 ml of 1% potassium permanganate solution, and 20 ml of (5 + 95) sulfuric acid solution respectively to obtain standard solutions with different concentrations. Add 0.3 ml of 3% sodium sulfite solution to the sample solution and the above standard solutions respectively, shake well and let stand for 1 h. After standing, add 0.5 ml of 3-pentanone and 0.3 ml of 30% hydrogen peroxide respectively, cover the stopper and shake well to mix. After the derivatization reaction for 20 min, add 5 ml of n-hexane and shake vigorously for 20 s. After standing and separating, draw 3.5 ml of the upper n-hexane layer into a 15-ml centrifuge tube, add 10 ml of water and shake vigorously for 20 s. After standing and separating, take the upper clear liquid and transfer it to an injection vial to obtain the test sample solution and the reference solution.

[0037] (5)Gas-phase testing: Use a 35%-trifluoropropyl-methyl polysiloxane stationary phase capillary column (DB-200) for testing. The chromatographic conditions are as follows: injection port temperature 260 °C, split ratio 10:1, carrier gas flow rate 1 ml / min, initial column temperature 55 °C, hold for 5 min, increase the temperature to 110 °C at a rate of 10 °C / min and then increase the temperature to 280 °C at a rate of 70 °C / min and hold for 5 min. ECD detector temperature 300 °C, injection volume 1 μl. Inject the test sample solution and the reference solution for testing respectively, record the peak areas, and calculate the iodine content using the standard curve method.

[0038] The chromatograms of the reference solution and the test sample solution in this example are shown in Appendix Figure 1 and Appendix Figure 2 .

[0039] Example 2 Crucible Comparison Weigh 10g of food for special medical purposes (hereinafter referred to as FSMP) and add 30ml of warm water at approximately 40°C. Ultrasonicate for 30 minutes. After cooling, add water to 100ml. Shake well to obtain a sample suspension. Three 5ml aliquots of the sample suspension were added to porcelain crucibles. Sample 1 was used as a background, and samples 2 and 3 were added with 0.35ml of the reference working solution (iodine concentration of 1.0151μg / ml). Another three 5ml aliquots of the sample suspension were added to quartz crucibles. Sample 1 was used as a background, and samples 2 and 3 were added with 0.35ml of the reference working solution (iodine concentration of 1.0151μg / ml). Another three 5ml aliquots of the sample suspension were added to nickel crucibles. Sample 1 was used as a background, and samples 2 and 3 were added with 0.35ml of the reference working solution (iodine concentration of 1.0151μg / ml). All samples were measured according to the method in Example 1. The results are shown in Table 1. Here, "equivalent to" means the weight of the special medical food that should be contained in each 5 ml sample suspension obtained by concentration calculation after 10 g of special medical food is added to water and ultrasonically treated to constant volume.

[0040] Table 1 Comparison of ashing recovery rates of different crucibles

[0041] The test results in Table 1 show that the recovery rate of nickel crucibles is higher. The reason for the lower recovery rates of porcelain and quartz crucibles may be that potassium hydroxide corrodes the crucible during the ashing process, forming a glassy layer of melt. This corrosion layer encapsulates some iodine, resulting in a lower recovery rate.

[0042] Example 3 Comparison of Ketone Derivatization Reagents Derivatization treatment was performed using 2-butanone and 3-pentanone as derivatization reagents, respectively, and the sensitivity of the two derivatization reagents was compared: two sets of 5 standard solutions of different concentrations were prepared according to the method of Example 1, and 3-pentanone and 2-butanone were used as derivatization reagents to prepare test solutions, respectively. The same conditions as in Example 1 were used for testing. The results are shown in Table 2 below.

[0043] Table 2 Comparison of derivatization reagents

[0044] From the results in Table 2, it can be seen that for the same amount of iodine under the same experimental conditions, the response of 3-pentanone as a derivatization reagent is twice as high as that of 2-butanone, indicating that 3-pentanone has higher sensitivity as a derivatization reagent.

[0045] Comparative Example 1 The method described in Example 1 of Chinese Patent Publication No. CN104215706A was used to determine the iodine content in formula foods for special medical purposes. The test samples in Comparative Example 1 and Example 1 were the same.

[0046] The same batch of special medical foods was tested according to the methods of Example 1 and Comparative Example 1, and a spike recovery experiment was carried out. ① Test of Comparative Example 1: Weigh 0.5 g of a certain special medical food in triplicate and add it to a porcelain crucible. Sample No. 1 was used as the blank, and 0.3 ml of the reference substance working solution (iodine concentration: 1.0151 μg / ml) was added to Samples No. 2 and No. 3, and the test was carried out according to the method described in Comparative Example 1; ② Test of Example 1: Weigh 5 g of the same batch of special medical food, dissolve it in water, make up the volume to 50 ml, shake well, and prepare a sample suspension according to the method of Example 1. Take 5 ml of the sample suspension in triplicate and add it to a nickel crucible. Sample No. 1 was used as the blank, and 0.3 ml of the reference substance working solution (iodine concentration: 1.0151 μg / ml) was added to Samples No. 2 and No. 3, and the test was carried out according to the method of Example 1. During the test, the samples in Comparative Example 1 were not completely ashed. After the ashing was completed, there were still carbon particles remaining after dissolving with a sulfuric acid aqueous solution. The samples by the method of Example 1 were completely ashed. After the ashing was completed, the solution was colorless and clear after dissolving with a sulfuric acid aqueous solution and reducing with sodium sulfite. See the appendix for details. Figure 3 Among them, Samples A - C represent Samples No. 1 - No. 3 of Example 1, and Samples D - F represent Samples No. 1 - No. 3 of Comparative Example 1. The recovery test results are shown in Table 3 below. After the present invention uses potassium permanganate - potassium hydroxide - potassium nitrate for ashing, potassium manganate is generated in the ashing residue. Potassium permanganate is generated after dissolving with a sulfuric acid aqueous solution. The addition of sodium sulfite for reduction is to eliminate the interference of excess potassium permanganate on the derivatization reaction.

[0047] Table 3 Comparison of recovery rates between Example 1 and Comparative Example 1

[0048] It can be seen from the results in Table 3 that the method of Comparative Example 1 is not applicable to the detection of special medical foods. In order to explore the reasons for the inapplicability of this method, the present invention further carried out the following tests: Weigh 0.5 g of special medical food in quadruplicate and add it to a porcelain crucible, and carry out ashing according to the method described in Comparative Example 1 to obtain four ashing residues. The four residues were dissolved with a sulfuric acid solution, mixed together, and made up the volume to 50 ml. Take 10 ml of the mixed solution in quadruplicate. Among them, Solution No. 1 was used as the blank solution, and 0.3 ml of the reference substance working solution (iodine concentration: 1.0151 μg / ml) was added to Solutions No. 2 - No. 4, and derivatization - gas phase determination was carried out respectively. The results are shown in Table 4 below.

[0049] Table 4 Spike recovery rate of the ashing residue in Comparative Example 1

[0050] The results in Table 4 indicate that matrix interference is present in the dissolved residue, and this ashing method is ineffective in removing matrix interference from FSMPs. The overall recovery rate for the method in Comparative Example 1, shown in Table 3, is only 30%-40%, significantly different from the spiked residue recovery rates in Table 4. This suggests that some iodine is lost during the ashing process in the FSMPs.

[0051] Comparative Example 2 Comparison of Alkali Ashing Reagents Two different ashing reagent combinations, potassium nitrate-potassium hydroxide and potassium nitrate-potassium hydroxide-potassium permanganate, were used to test the same batch of special medical foods according to the method of Example 1, and spiked recovery experiments were conducted. The total spiked recovery and the residue spiked recovery were tested. The total spiked recovery was tested by taking three 5ml portions of the same sample suspension, adding them to nickel crucibles, and adding 0.3ml of a reference substance working solution (iodine concentration of 1.0151 μg / ml) to each portion. Testing was performed according to the method of Example 1, and the total spiked recovery was calculated by comparing the iodine content with that of the background sample. The residue spiked recovery was tested by taking two portions of the sample ashing residue, dissolving them in water, and transferring them to the same 50ml volumetric flask to volume. Two 20ml portions of the solution were taken, one portion added with 0.3ml of the reference substance working solution (iodine concentration of 1.0151 μg / ml), and the other portion was added with 0.3ml of water. The iodine content of the two solutions was determined according to the derivatization and determination methods described in Example 1 to obtain the residue spiked recovery.

[0052] When using potassium nitrate-potassium hydroxide for ashing, the degree of sample ashing was significantly affected by the ashing time. After ashing in a muffle furnace for 60 minutes, a large amount of carbon particles remained in the sample. However, extending the ashing time to 100 minutes completely ashed the sample, leaving no carbon particles. The total recovery and residue spike recovery at different ashing times were tested, and the results are shown in Table 5.

[0053] Table 5 Potassium nitrate-potassium hydroxide ashing spike recovery

[0054] The results show that when potassium nitrate-potassium hydroxide is used for ashing, when the ashing time is short, the matrix interference in the FSMP samples cannot be effectively removed, resulting in poor parallelism of the test results and low recovery rate; when the ashing time is long, the matrix interference in the FSMP samples can be effectively removed, but a large amount of iodine is lost during the ashing process, resulting in poor parallelism of the test results and low recovery rate.

[0055] Adding 0.3 ml of 1% potassium permanganate solution before sample treatment can increase the ashing efficiency and prevent iodine loss during the ashing process, as shown in Table 6 below.

[0056] Table 6 Potassium nitrate-potassium hydroxide-potassium permanganate ashing spike recovery

[0057] Ashing with potassium nitrate - potassium hydroxide - potassium permanganate for 60 min can achieve the effect of complete ashing. By comparing the spike recovery test results of the two ashing reagent combinations, it can be seen that adding potassium permanganate can accelerate the ashing of the sample and avoid the loss of iodine during the ashing process.

[0058] Using an equimolar amount of manganese dioxide (1.7 mg) to replace potassium permanganate for ashing, with the other conditions the same as in Example 1, the results can also achieve a comparable recovery effect, as shown in Table 7 specifically.

[0059] Table 7 Spike recovery rate of potassium nitrate - potassium hydroxide - manganese dioxide ashing

[0060] Test Example 1 Recovery rate test Weigh 10 g of a particular medical food, add about 30 ml of warm water at 40 °C, perform ultrasonic treatment for 30 min, cool and then make up the volume to 100 ml with water and shake well to obtain a sample suspension. Take 12 nickel crucibles, add 5 ml of the sample suspension to each. Samples 1 - 3 are used as background samples (Background 1 - Background 3), samples 4 - 6 are respectively added with 0.18 ml of the reference substance working solution (iodine concentration is 1.0151 μg / ml) (Low concentration 1 - Low concentration 3), samples 7 - 9 are respectively added with 0.35 ml of the reference substance working solution (iodine concentration is 1.0151 μg / ml) (Medium concentration 1 - Medium concentration 3), and samples 10 - 12 are respectively added with 0.7 ml of the reference substance working solution (iodine concentration is 1.0151 μg / ml) (High concentration 1 - High concentration 3). Measure according to the method of Example 1, and the recovery rate test results are shown in Table 8 and Table 9 below.

[0061] Table 8 Test results of background samples

[0062] Table 9 Test results of spike recovery rate of spiked samples

[0063] From the test results, it can be seen that within the range of 50% - 200% of the content, spike recovery tests are carried out at three concentration levels of low, medium, and high. The measured recovery rate is 94.2% - 100.2%, the average recovery rate is 97.4% (n = 9), and the measured RSD is 2.0%. This shows that the accuracy test of the method of the present invention meets the requirements, and the measurement method is accurate and reliable.

[0064] Test Example 2 Eight approved iodine-containing special medical foods were randomly selected and tested according to the first method of the national standard GB5009.267-2020 - inductively coupled plasma mass spectrometry (ICP-MS method) and the method of Example 1, respectively. The measurement results are shown in Table 10 below.

[0065] Table 10 Comparison of test results between Example 1 and ICP-MS method

[0066] It can be seen from the measurement results that the relative average deviation between the measurement results of Example 1 and the test results of the first method of the national standard GB5009.267-2020 is less than 5%, indicating that the test results of the method of the present invention are accurate and can be used as an alternative method to the inductively coupled plasma mass spectrometry method.

[0067] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or change without departing from the present invention shall be included within the scope of the technical solution of the present invention.

Claims

1. A method for determining the iodine content in a formula food for special medical purposes, characterized in that, It includes the following steps: (1) Prepare the reference solution working solution: Weigh potassium iodide, dissolve it in water to obtain the reference solution working solution; (2) Alkaline ashing treatment: Add water to the test sample to obtain a sample suspension, and perform alkaline ashing treatment to obtain a sample solution; (3) Derivatization treatment: Add sulfuric acid solution and the reagent used in the alkaline ashing treatment in step (2) to the reference solution working solution, and then perform derivatization treatment and organic solvent extraction on the reference solution working solution and the sample solution respectively to obtain a reference solution and a test sample solution; (4) Testing: Inject the reference solution and the test sample solution respectively, and perform testing by gas chromatography to calculate the iodine content; The reagent used in the alkaline ashing treatment is potassium hydroxide solution, potassium nitrate solution and manganese-containing reagent, and the manganese-containing reagent is at least one of potassium permanganate solution and manganese dioxide; The derivatization treatment includes adding sodium sulfite solution, standing still, and adding a ketone reagent and hydrogen peroxide solution for a derivatization reaction.

2. The measurement method according to claim 1, characterized in that, The alkaline ashing treatment in step (2) is carried out in a nickel crucible.

3. The measurement method according to claim 1, characterized in that, The ketone reagent includes 3-pentanone.

4. The measurement method according to claim 1, characterized in that The gas chromatography in step (4) is carried out using a capillary column with a 35%-trifluoropropyl-methyl polysiloxane stationary phase for testing.

5. The measurement method according to claim 1, wherein The concentration of the potassium hydroxide solution is 29%, and the volume-mass ratio with the test sample is 3 - 5 ml / g; the concentration of the potassium nitrate solution is 20%, and the volume-mass ratio with the test sample is 3 - 5 ml / g; the concentration of the potassium permanganate solution is 1%, and the volume-mass ratio with the test sample is 0.6 - 0.9 ml / g; and / or the mass ratio of manganese dioxide to the test sample is 0.003 - 0.005 g / g.

6. The measurement method according to claim 1, characterized in that, The alkaline ashing treatment also includes evaporating the water after adding the potassium hydroxide solution, potassium nitrate solution and manganese-containing reagent, heating up to 280 °C, maintaining for 40 - 60 min, then heating to 600 °C and keeping for 40 - 80 min, adding water to dissolve the residue to obtain a sample solution.

7. The measurement method according to claim 1, wherein The concentration of the sodium sulfite solution is 3%, the standing time is 60 - 90 min, and the concentration of the hydrogen peroxide solution is 30%.

8. The measurement method according to claim 1, characterized in that, The time of the derivatization reaction is 20 - 60 min, and the organic solvent is n-hexane.

9. The measurement method according to claim 1, characterized in that, The chromatographic conditions of the gas chromatography in step (4) include: split ratio 10:1; carrier gas flow rate 1 ml / min; initial column temperature 55 °C, maintaining for 5 min, heating at a rate of 10 °C / min to 110 °C and then heating at a rate of 70 °C / min to 280 °C and maintaining for 5 min.

10. The measurement method according to claim 1, characterized in that The chromatographic conditions of the gas chromatography in step (4) include: injection port temperature 260 °C, ECD detector temperature 300 °C, injection volume 1 μl.

Images