A method for determining iodine content in foods for special medical purposes

Abstract

The present invention relates to the technical field of food testing, and more particularly to a method for determining the iodine content in a food formulated for special medical purposes. The method comprises the following steps: (1) weighing potassium iodide and dissolving it in water to obtain a reference working solution; (2) adding water to a test sample to obtain a sample suspension, and subjecting the suspension to an alkali ashing treatment to obtain a sample solution; (3) adding a sulfuric acid solution and a reagent used for the alkali ashing treatment to the reference working solution, and subjecting the sample solution to a derivatization treatment and organic solvent extraction to obtain a reference solution and a test solution; (4) testing the sample solution using gas chromatography to calculate the iodine content; the reagents used for the alkali ashing treatment are potassium hydroxide solution, potassium nitrate solution, and potassium permanganate solution (or manganese dioxide); the derivatization treatment comprises adding a sodium sulfite solution, allowing the solution to stand, and then adding a ketone reagent and a hydrogen peroxide solution to carry out a derivatization reaction. The present invention has the advantages of low cost, high safety, and high accuracy.

Description

Technical Field

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

[0002] Foods for special medical purposes (FSMPs), or FSMPs, are specially formulated to meet the specific nutrient or dietary needs of individuals with restricted food intake, digestive and absorption disorders, metabolic disorders, or specific disease states. Iodine is an essential trace element for the human body and is often added to FSMPs as a nutrient. Excessive iodine intake can lead to thyroid dysfunction and affect human health. Therefore, during the formulation process for FSMPs, the iodine content must be adjusted to meet the user's physiological characteristics and nutritional needs. Therefore, using appropriate methods to determine the iodine content in FSMPs is crucial for their development and quality control.

[0003] Currently, the iodine content in special medical foods is primarily determined using Method 1 of GB5009.267-2020, "National Food Safety Standard for the Determination of Iodine in Foods," inductively coupled plasma mass spectrometry (ICP-MS). The main steps include weighing a homogenized sample, adding the extraction solution, vortexing until the sample is evenly dispersed, extracting in a constant-temperature drying oven or water bath shaker, cooling, and then adjusting the volume. High-speed centrifugation is performed, and the supernatant is filtered. ICP-MS is used for determination using potassium iodide as a standard, with the addition of internal standard elements (one or more of tellurium, rhodium, indium, and rhenium). The iodine content in the sample is determined using a calibration curve. The main advantages of this method are simple sample pretreatment, rapid measurement, and high sensitivity. However, the low penetration of ICP-MS instruments, the high cost of use and maintenance, and the toxicity of tetramethylammonium hydroxide used in the test process have limited its application.

[0004] Chinese Patent Publication No. CN104215706A discloses a gas chromatography analysis method for determining the iodine content in food, which includes the following steps:

[0005] (1) Sample ashing: Weigh 0.2g-0.5g of sample and place it in a porcelain crucible. Add 1ml of 10% potassium carbonate solution and 1ml of 10% zinc sulfate solution to soak the sample, mix well, and heat until no smoke is generated. Place the sample in a muffle furnace for ashing and cool.

[0006] (2) Sample derivatization: Dissolve the incinerated product in 10 ml of 0.15 mol / L sulfuric acid solution, then add 1 ml of butanone and 2 ml of 3.5% H2O2, vortex to mix, and let stand;

[0007] (3) Sample extraction: extract with n-hexane, combine the organic phases, wash with distilled water until neutral, let stand, and take the supernatant as the test solution;

[0008] (4) Sample injection detection: Use gas chromatography to determine the iodine content in the test solution.

[0009] 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, carbon particles still remain after dissolution with sulfuric acid aqueous solution, indicating incomplete ashing, matrix interference in the dissolved residue, and iodine loss during the ashing process, resulting in low accuracy of the test results.

[0010] 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

[0011] 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 formula foods with low cost, high safety and high accuracy.

[0012] The present invention is achieved through the following technical solutions:

[0013] The present invention provides a method for determining the iodine content in a special medical purpose formula food, comprising the following steps:

[0014] (1) Prepare the reference substance working solution: Weigh potassium iodide and dissolve it in water to obtain the reference substance working solution;

[0015] (2) Alkali ashing treatment: Add water to the test sample to obtain a sample suspension, and then perform alkaline ashing treatment to obtain a sample solution;

[0016] (3) Derivatization treatment: add sulfuric acid solution and the reagent used for alkaline ashing treatment in step (2) to the reference working solution, and then perform derivatization treatment and organic solvent extraction on the sample solution to obtain the reference solution and the test solution;

[0017] (4) Testing: The reference solution and the test solution were injected separately, tested by gas chromatography, and the iodine content was calculated;

[0018] The reagents used in the alkaline ashing treatment are potassium hydroxide solution, potassium nitrate solution and a manganese-containing reagent, and the manganese-containing reagent is at least one of potassium permanganate solution and manganese dioxide;

[0019] The derivatization treatment includes adding a sodium sulfite solution, allowing the solution to stand, and then adding a ketone reagent and a hydrogen peroxide solution to carry out a derivatization reaction.

[0020] The present invention uses potassium hydroxide solution, potassium nitrate solution, and potassium permanganate solution, or potassium hydroxide solution, potassium nitrate solution, and manganese dioxide during the alkaline ashing process. Potassium hydroxide serves as a fixative, potassium nitrate serves as an oxidant, and the potassium permanganate or manganese dioxide accelerates the ashing process and prevents iodine loss during the ashing process. After the ashing residue is dissolved, it is reduced with sodium sulfite to obtain a clear, colorless solution, which completely eliminates interference from the organic matrix. At the same time, no iodine is lost during the ashing process.

[0021] The potassium permanganate in the ashing reagent of the present invention is immediately reduced to tetravalent manganese upon addition to the sample and loses its oxidizing property. Therefore, its main function is not to act as an oxidant, but to catalyze and accelerate the ashing process and prevent the volatilization of iodine during the ashing process.

[0022] As an embodiment of the present invention, the alkali ashing treatment in step (2) is performed in a nickel crucible. Compared with crucibles made of other materials, such as quartz crucibles and porcelain crucibles, nickel crucibles can improve the recovery rate of iodine.

[0023] 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.

[0024] As an embodiment of the present invention, the gas chromatography method in step (4) is tested using a 35%-trifluoropropyl-methylpolysiloxane stationary phase capillary column.

[0025] As an embodiment of the present invention, the concentration of the potassium hydroxide solution is 29%, and the volume mass ratio of the potassium hydroxide solution to the test sample is 3-5 ml / g.

[0026] As an embodiment of the present invention, the concentration of the potassium nitrate solution is 20%, and the volume mass ratio of the potassium nitrate solution to the test sample is 3-5 ml / g.

[0027] As an embodiment of the present invention, the concentration of the potassium permanganate solution is 1%, the volume mass ratio of the potassium permanganate solution to the test sample is 0.6~0.9ml / g, and the mass ratio of manganese dioxide to the test sample is 0.003~0.005g / g.

[0028] As an embodiment of the present invention, the alkaline ashing treatment further includes adding potassium hydroxide solution, potassium nitrate solution and manganese-containing reagent, evaporating water, heating to 280°C, maintaining for 40 to 60 minutes, then heating to 600°C and maintaining for 40 to 80 minutes, adding water to dissolve the residue to obtain a sample solution.

[0029] As an embodiment of the present invention, during the derivatization process, the concentration of the sodium sulfite solution is 3%, the standing time is 60-90 minutes, and the concentration of the hydrogen peroxide solution is 30%.

[0030] As an embodiment of the present invention, the derivatization reaction time is 20 to 60 minutes, and the organic solvent is n-hexane.

[0031] As an embodiment of the present invention, the chromatographic conditions of the gas chromatography method in step (4) include: a split ratio of 10:1; a carrier gas flow rate of 1 ml / min; an initial column temperature of 55°C, maintained for 5 minutes, 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 maintained for 5 minutes.

[0032] As an embodiment of the present invention, the chromatographic conditions of the gas chromatography method in step (4) include: an injection port temperature of 260°C, an ECD detector temperature of 300°C, and an injection volume of 1 μl.

[0033] The food for special medical purposes (FSMP) of the present invention usually requires the addition of multiple nutritional compounds. In order to extend shelf life and stabilize product quality, these nutritional compounds are processed using special processes (for example, oil-based nutrients are encapsulated using microcapsules). These processing processes inevitably introduce some factors that interfere with the determination of iodine content. This situation makes the iodine content determination method applicable to general foods ineffective when applied to FSMP.

[0034] The present invention provides a method for determining iodine content in foods for special medical purposes that is safe, low-cost, widely applicable, and highly sensitive. The present invention tested the effectiveness of various iodine content determination methods for foods for special medical purposes and found that alkaline ashing-gas chromatography offers greater safety and lower detection costs. The present invention improves upon existing technologies, including but not limited to the selection of alkaline ashing reagents, to facilitate the detection of foods for special medical purposes. Compared to inductively coupled plasma mass spectrometry (ICP-MS), the present method utilizes only conventional analytical instruments and avoids highly toxic reagents. Its sensitivity is comparable to that of ICP-MS, offering the advantages of low cost, widespread applicability, and safe operation.

[0035] The beneficial effects of the present invention are:

[0036] The present invention adds potassium nitrate and a manganese-containing reagent during the ashing process, and uses potassium hydroxide as a fixative, so that the sample can be completely ashed. After the ashing residue is dissolved, it is reduced with sodium sulfite to obtain a clear and colorless solution, which can completely eliminate the interference of the organic matrix. At the same time, no iodine is lost during the ashing process.

[0037] The present invention uses 3-pentanone as a derivatization reagent, which doubles the sensitivity compared to the existing method using butanone.

[0038] The present invention avoids the use of highly toxic reagents, and the operation process is safer.

[0039] The present invention only requires the use of conventional laboratory analytical instruments, has lower detection costs, and has strong popularization and applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is the chromatogram of the reference substance solution of Example 1.

[0041] Figure 2 The chromatogram of the test solution of Example 1 is shown in FIG.

[0042] Figure 3 The solution obtained by dissolving the FSMP food in sulfuric acid after ashing and then reducing it with sodium sulfite in Example 1 is compared with the solution obtained by dissolving the FSMP food in sulfuric acid after ashing in Comparative Example 1. DETAILED DESCRIPTION

[0043] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, these embodiments are merely exemplary and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solutions of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, and such modifications and replacements fall within the scope of protection of the present invention.

[0044] The special medical purpose formula food used in each embodiment of the present invention is Jiangzhong Chuyuan special medical purpose complete nutrition formula food.

[0045] Example 1

[0046] A method for determining the iodine content in a food for special medical purposes comprises the following steps:

[0047] (1) Prepare the reference substance working solution: Accurately weigh about 13 mg of potassium iodide (pre-dried in a silica gel desiccator for 24 hours), dissolve it in water and make up to 100 ml, shake well, take 1 ml and add water to make up to 100 ml, shake well to prepare the reference substance working solution.

[0048] (2) Preparation of reagents: ① 29% potassium hydroxide (w / w) solution: weigh 40 g potassium hydroxide (AR), add 100 ml water to dissolve, and cool to obtain; ② 20% potassium nitrate (w / w) solution: weigh 25 g potassium nitrate (AR), add 100 ml water to dissolve, and return to room temperature to obtain; ③ 1% potassium permanganate (w / v) solution: weigh 0.1 g potassium permanganate (AR), add 10 ml water to dissolve, and prepare it before use; ④ (5+95) sulfuric acid solution: slowly add 50 ml sulfuric acid to 950 ml water, stirring while adding, and dissolve and cool to obtain; ⑤ 3% sodium sulfite (w / v) solution: dissolve 0.3 g sodium sulfite in 10 ml water, and prepare it before use.

[0049] (3) Alkali ashing: Accurately weigh about 5 g of the test sample (special medical purpose formula food) powder, place it in a 50 ml volumetric flask, add 15 ml of warm water at about 40°C, ultrasonically treat for 30 min, let it cool, dilute to the mark with water, shake well, and 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, shake gently to mix, place it in an oven at 180°C for 2 hours to evaporate the water, cover the crucible and heat it to 280°C, maintain it for 40 minutes, remove it after taking it out, remove the crucible cover, place it in a muffle furnace and heat it to 600°C for 1 hour. After 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-capped test tube, wash it twice with 20 ml of (5+95) sulfuric acid solution and transfer it to the same screw-capped test tube to obtain the sample solution.

[0050] (4) Derivatization: Take 0.1 ml, 0.3 ml, 0.5 ml, 1 ml, and 1.5 ml of the reference working solution in 50 ml screw-capped test tubes, respectively. Add 1.6 ml, 1.4 ml, 1.2 ml, 0.7 ml, and 0.2 ml of water, respectively. Then, 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 to obtain standard solutions of different concentrations. Add 0.3 ml of 3% sodium sulfite solution to the sample solution and the above standard solutions, shake well, and let stand for 1 hour. After standing, add 0.5 ml of 3-pentanone and 0.3 ml of 30% hydrogen peroxide respectively, cover the stopcock and shake to mix. After 20 minutes of derivatization, add 5 ml of n-hexane and shake vigorously for 20 seconds. After standing and stratification, 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 seconds. After standing and stratification, take the upper supernatant into the injection bottle to obtain the test solution and reference solution.

[0051] (5) Gas phase method: A 35% trifluoropropyl-methylpolysiloxane stationary phase capillary column (DB-200) was used for the test. The chromatographic conditions were 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, temperature increased at a rate of 10°C / min to 110°C, then at a rate of 70°C / min to 280°C, hold for 5 min. The ECD detector temperature was 300°C, and the injection volume was 1 μl. The test solution and the reference solution were injected separately for testing, and the peak area was recorded. The iodine content was calculated using the standard curve method.

[0052] The chromatograms of the reference solution and the test solution in this example are shown in the attached Figure 1 and attached Figure 2 .

[0053] Example 2

[0054] Crucible Comparison

[0055] 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.

[0056] Table 1 Comparison of ashing recovery rates of different crucibles

[0057]

[0058] 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.

[0059] Example 3

[0060] Comparison of Ketone Derivatization Reagents

[0061] 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.

[0062] Table 2 Comparison of derivatization reagents

[0063]

[0064] 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.

[0065] Comparative Example 1

[0066] The iodine content in the food for special medical purposes was determined by referring to the method described in Example 1 of Chinese Patent Publication No. CN104215706A. The samples for determination in Comparative Example 1 and Example 1 were the same.

[0067] The same batch of FSMP was tested according to the methods of Example 1 and Comparative Example 1, and spike recovery experiments were performed. ① Comparative Example 1 Test: Three 0.5g portions of a FSMP were weighed and placed in porcelain crucibles. Sample #1 was used as the background. Samples #2 and #3 were added with 0.3ml of the reference substance working solution (iodine concentration: 1.0151μg / ml) and tested according to the method described in Comparative Example 1. ② Example 1 Test: 5g of the same batch of FSMP was weighed, dissolved in water to a volume of 50ml, and shaken well. Sample suspensions were prepared according to the method of Example 1. Three 5ml portions of the sample suspension were placed in nickel crucibles. Sample #1 was used as the background. Samples #2 and #3 were added with 0.3ml of the reference substance working solution (iodine concentration: 1.0151μg / ml) and tested according to the method of Example 1. During the test, the sample of Comparative Example 1 was not completely ashed. After the ashing was completed, sulfuric acid aqueous solution was added to dissolve it, and carbon particles still remained. The sample of Example 1 was completely ashed. After the ashing was completed, sulfuric acid aqueous solution was added to dissolve it, and the solution was colorless and clear after sodium sulfite reduction. See the attached Figure 3 . Among them, Sample A to Sample C represent Sample No. 1 to Sample No. 3 of Example 1, and Sample D to Sample F represent Sample No. 1 to Sample No. 3 of Comparative Example 1. The recovery test results are shown in Table 3 below. In the present invention, after potassium permanganate-potassium hydroxide-potassium nitrate is used for ashing, potassium manganate is generated in the ashing residue, which is dissolved by adding sulfuric acid aqueous solution to generate potassium permanganate. Sodium sulfite is added for reduction in order to eliminate the interference of excess potassium permanganate with the derivatization reaction.

[0068] Table 3 Comparison of recovery rates between Example 1 and Comparative Example 1

[0069]

[0070] The results in Table 3 indicate that the method in Comparative Example 1 is not suitable for testing FSMPs. To explore the reasons for this method's inapplicability, the present inventors conducted the following tests: Four portions of 0.5 g of FSMP were weighed and placed in porcelain crucibles. Ashing was performed according to the method described in Comparative Example 1, yielding four portions of ash residue. These four portions were dissolved in sulfuric acid solution and mixed together to a final volume of 50 ml. Four 10 ml portions of the mixed solution were taken, with solution No. 1 serving as the background solution. Solutions Nos. 2-4 were each added with 0.3 ml of the reference substance working solution (iodine concentration: 1.0151 μg / ml). Derivatization-gas phase analysis was performed on each portion. The results are shown in Table 4.

[0071] Table 4 Recovery rate of spiked ash residue in comparative example 1

[0072]

[0073] 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.

[0074] Comparative Example 2

[0075] Comparison of Alkali Ashing Reagents

[0076] 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.

[0077] 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.

[0078] Table 5 Potassium nitrate-potassium hydroxide ashing spike recovery

[0079]

[0080] 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.

[0081] 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.

[0082] Table 6 Potassium nitrate-potassium hydroxide-potassium permanganate ashing spike recovery

[0083]

[0084] Complete ashing can be achieved by using potassium nitrate-potassium hydroxide-potassium permanganate for 60 minutes. Comparison of the spiked recovery test results of the two ashing reagent combinations shows that the addition of potassium permanganate can accelerate the ashing of the sample while avoiding iodine loss during the ashing process.

[0085] An equal amount of manganese dioxide (1.7 mg) was used instead of potassium permanganate for ashing. The other conditions were the same as those in Example 1. The results also achieved a comparable recovery rate, as shown in Table 7.

[0086] Table 7 Recovery of spiked potassium nitrate-potassium hydroxide-manganese dioxide ashing

[0087]

[0088] Test Example 1

[0089] Recovery test

[0090] Weigh 10g of a special medical food and add 30ml of warm water at approximately 40°C. Ultrasonicate for 30 minutes. After cooling, add water to 100ml and shake thoroughly to obtain a sample suspension. Twelve nickel crucibles were each filled with 5ml of the sample suspension. Samples 1-3 served as background samples (Background 1-Background 3). Samples 4-6 were each added with 0.18ml of the reference working solution (iodine concentration: 1.0151μg / ml) (Low Concentration 1-Low Concentration 3). Samples 7-9 were each added with 0.35ml of the reference working solution (iodine concentration: 1.0151μg / ml) (Medium Concentration 1-Medium Concentration 3). Samples 10-12 were each added with 0.7ml of the reference working solution (iodine concentration: 1.0151μg / ml) (High Concentration 1-High Concentration 3). Determination was performed according to the method in Example 1. The recovery test results are shown in Tables 8 and 9 below.

[0091] Table 8 Background sample test results

[0092]

[0093] Table 9 Recovery test results of spiked samples

[0094]

[0095] The test results show that within the range of 50% to 200% of the content, the recovery rate of the sample addition test was 94.2% to 100.2% at three concentration levels: low, medium, and high. The average recovery rate was 97.4% (n=9) and the RSD was 2.0%. This shows that the accuracy test of the method of the present invention meets the requirements and the determination method is accurate and reliable.

[0096] Test Example 2

[0097] Eight approved iodine-containing special medical foods were randomly selected and tested according to the first method of national standard GB5009.267-2020 - inductively coupled plasma mass spectrometry (ICP-MS method) and the method of Example 1. The test results are shown in Table 10 below.

[0098] Table 10 Comparison of test results of Example 1 and ICP-MS method

[0099]

[0100] It can be seen from the measurement results that the relative average deviations between the measurement results of Example 1 and the test results of the first method of national standard GB5009.267-2020 are less than 5%, indicating that the test results of the method of the present invention are accurate and can be used as an alternative to inductively coupled plasma mass spectrometry.

[0101] 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 modification that does not depart from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A method for determining iodine content in a food for special medical purposes, characterized in that: The steps include: (1) Prepare the reference substance working solution: Weigh potassium iodide and dissolve it in water to obtain the reference substance working solution; (2) Alkali ashing treatment: Add water to the test sample to obtain a sample suspension, and then perform alkaline ashing treatment to obtain a sample solution; (3) Derivatization treatment: add sulfuric acid solution and the reagent used for alkaline ashing treatment in step (2) to the reference working solution, and then perform derivatization treatment and organic solvent extraction on the sample solution to obtain the reference solution and the test solution; (4) Testing: The reference solution and the test solution were injected separately, tested by gas chromatography, and the iodine content was calculated; The reagents used in the alkaline ashing treatment are potassium hydroxide solution, potassium nitrate solution and a manganese-containing reagent, and the manganese-containing reagent is at least one of potassium permanganate solution and manganese dioxide; The derivatization treatment includes adding a sodium sulfite solution, allowing the solution to stand, and then adding a ketone reagent and a hydrogen peroxide solution to carry out a derivatization reaction.

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

3. The measuring method according to claim 1, wherein The ketone reagent includes 3-pentanone.

4. The measuring method according to claim 1, wherein The gas chromatography method described in step (4) is tested using a 35%-trifluoropropyl-methylpolysiloxane stationary phase capillary column.

5. The measuring method according to claim 1, wherein The concentration of the potassium hydroxide solution is 29%, and the volume mass ratio of the test sample is 3-5 ml / g; the concentration of the potassium nitrate solution is 20%, and the volume mass ratio of the test sample is 3-5 ml / g; the concentration of the potassium permanganate solution is 1%, and the volume mass ratio of 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 measuring method according to claim 1, wherein The alkaline ashing treatment further includes adding potassium hydroxide solution, potassium nitrate solution and manganese-containing reagent, evaporating water, heating to 280° C., maintaining for 40 to 60 minutes, then heating to 600° C., maintaining for 40 to 80 minutes, and adding water to dissolve the residue to obtain a sample solution.

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

8. The measuring method according to claim 1, wherein The derivatization reaction time is 20 to 60 minutes, and the organic solvent is n-hexane.

9. The measuring method according to claim 1, wherein The chromatographic conditions of the gas chromatography method in step (4) include: a split ratio of 10:1; a carrier gas flow rate of 1 ml / min; an initial column temperature of 55°C, maintained for 5 minutes, 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 maintained for 5 minutes.

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

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