Method for detecting organic iodine in seaweed

Abstract

The invention provides a method for detecting organic iodine in seaweed, which belongs to the technical field of organic iodine detection, and comprises the following steps: drying, crushing and sieving a seaweed sample to obtain seaweed powder; performing hydrolysis and concentration on the seaweed powder, and fixing the volume to obtain a test solution; preparing various organic iodine standard substance solutions, sucking the standard substance solutions, injecting the standard substance solutions into a liquid chromatograph, and recording the relative retention time and the peak area of each organic iodine in the standard substance solutions; the high performance liquid chromatography conditions are as follows: a C18 chromatographic column is used, a 0.1% TFA aqueous solution is used as a mobile phase A, acetonitrile is used as a mobile phase B, and gradient elution is performed; the detection wavelength is 280 nm; and sucking the test solution, injecting the test solution into a liquid chromatograph, and carrying out qualitative and quantitative analysis on the organic iodine in the test solution. According to the high performance liquid chromatography analysis method established by the invention, the amino acid derivative organic iodine in the sample can be quantitatively determined without being interfered by L-tyrosine, L-tryptophan and L-phenylalanine in the sample.

Description

Technical Field

[0001] The invention relates to the technical field of organic iodine detection, and in particular to a method for detecting organic iodine in seaweed. Background Art

[0002] The main forms of iodine in seaweed are inorganic iodine and organic iodine. Inorganic iodine in seaweed mainly exists in the form of iodide ions and a small amount of iodate, while organic iodine in seaweed is the product formed by the combination of iodine in seaweed with organic substances such as proteins, peptides, pigments, polyphenols, and polysaccharides. Hou et al. used neutron activation analysis to study the distribution of iodine in different biomacromolecules of Sargassum and found that iodine is mainly bound to proteins and less bound to other organic substances. Therefore, organic iodine in seaweed can be divided into amino acid derivatives and non-amino acid derivatives. Amino acid derivative organic iodine is the main form of organic iodine in seaweed. Tong et al. studied the metabolism of iodine in Nereocystis luetkeana and analyzed that most of the iodine was bound to tyrosine residues. Coulson found iodine-containing amino acids in the hydrolyzate of seaweed protein. Qualitative analysis showed that these iodine-containing amino acids were 3-iodo-L-tyrosine (monoiodotyrosine, MIT), 3,5-diiodo-L-tyrosine (3,5-diiodotyrosine, DIT), triiodothyronine (triiodothyronine, T3) and thyroxine (thyroxine, T4).

[0003] Kelp is a well-known iodine-rich food that is both a medicine and food. The Compendium of Materia Medica states that "kelp can cure goiter (i.e. goiter) and other edema diseases, and has the function of resolving phlegm and dispersing knots"; the iodine in kelp is composed of organic iodine and inorganic iodine, and the iodine-containing amino acids in organic iodine account for more than 50%. In recent years, foods with kelp extract (organic iodine) as additives have received attention, so it is urgent to establish an accurate and rapid method for detecting the content of organic iodine in amino acid derivatives in kelp. Summary of the invention

[0004] In view of the technical problems existing in the background technology, the present application provides a method for detecting organic iodine in seaweed, aiming to solve the technical problem of accurately and quickly detecting the organic iodine content of amino acid derivatives in kelp.

[0005] In a first aspect, the present application provides a method for detecting organic iodine in seaweed, comprising the following steps: S1. Sample pretreatment: drying, crushing and sieving the seaweed sample to obtain seaweed powder; S2. Preparation of test solution: the seaweed powder is hydrolyzed, concentrated, fixed to volume, and filtered to serve as the test solution; S3. Qualitative and quantitative analysis of organic iodine: prepare various organic iodine standard solutions, draw the standard solutions, inject into liquid chromatograph, record the relative retention time and peak area of ​​each organic iodine in the standard solutions; the HPLC conditions are: use C18 chromatographic column, 0.1% TFA aqueous solution as mobile phase A, acetonitrile as mobile phase B, gradient elution; detection wavelength is 280nm; The test solution is drawn in, injected into a liquid chromatograph, and a spectrum is obtained using the high performance liquid chromatography conditions. The organic iodine in the test solution is qualitatively analyzed according to the relative retention time of each organic iodine in the standard solution. A standard curve is established according to the peak area of ​​each organic iodine in the standard solution, and the organic iodine in the test solution is quantitatively analyzed according to the standard curve.

[0006] Preferably, the hydrolysis comprises the following steps: heating the seaweed powder in a 5 mol / L NaOH solution for hydrolysis, the solid-liquid ratio of the seaweed powder to the NaOH solution being 1:(5-10), the heating temperature being 110°C, and filtering after hydrolysis for 12 hours to obtain a hydrolyzate.

[0007] In the technical solution of the embodiment of the present application, organic iodine is combined with crude protein and exists in cells. The alkaline hydrolysis method can be used to dissolve the organic iodine in water, which is convenient for detection.

[0008] Preferably, the concentration comprises the following steps: adding acid to the hydrolyzate to adjust the pH to 7-9, filtering to obtain a filtrate, passing the filtrate through an HLB solid phase extraction column, washing the solid phase column with distilled water, eluting the HLB extraction column with 10% methanol, and finally eluting the extraction column with methanol to obtain an eluate, and concentrating the eluate under reduced pressure to dryness to obtain a sample to be tested.

[0009] In the technical solution of the embodiment of the present application, solid phase extraction is performed using a solid phase extraction column, which can separate, purify and concentrate the sample, improve the recovery rate of the analyte, effectively separate the analyte from the interfering components, reduce the sample pretreatment process, and is simple to operate, time-saving and labor-saving.

[0010] Preferably, the volume determination comprises the following steps: dissolving the sample to be tested in 0.4 mL of 0.005 mol / L NaOH solution, filtering through a 0.22 μm microporous filter membrane, and obtaining a test solution.

[0011] Preferably, in gradient elution, the volume ratio of mobile phase B in each time period is: 0-1 min, 20% mobile phase B; 1-15 min, 20%-50% mobile phase B; 15-30 min, 50%-80% mobile phase B; 30-35 min, 80%-20% mobile phase B.

[0012] Preferably, the C18 chromatographic column is an InertSustain AQ-C18 chromatographic column of 4.6×250 mm×5 μm.

[0013] Preferably, the column temperature of the chromatographic column is 30° C.; the flow rate of the eluent is 1 mL / min; and the injection volume is 10 μL.

[0014] Preferably, the organic iodine includes one or more of 3-iodo-L-tyrosine, 3,5-diiodo-L-tyrosine, triiodothyronine and thyroxine.

[0015] Preferably, the detection limit of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine is 0.5 ng, and the detection limit of triiodothyronine and thyroxine is 1.0 ng.

[0016] Preferably, in step S1, the drying temperature is 40-80° C., and the product is sieved through a 60-mesh sieve after being crushed.

[0017] Different from the existing technical solutions, the beneficial effects of this application include: The high performance liquid chromatography analysis method established in the present application can quantitatively determine the amino acid derivative organic iodine in the sample, namely 3-iodo-L-tyrosine (MIT), 3,5-diiodo-L-tyrosine (DIT), triiodothyronine (T3) and thyroxine (T4), without being interfered by L-tyrosine, L-tryptophan and L-phenylalanine in the sample; the concentration of the amino acid derivative organic iodine is in the range of 0.1-100 μg / mL, and shows a good linear relationship with the integrated area of ​​the chromatographic peak; according to the signal-to-noise ratio analysis of the spectrum, under the chromatographic analysis conditions, the detection limits of MIT and DIT are 0.5 ng, and the detection limits of T3 and T4 are 1.0 ng.

[0018] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 is a high performance liquid chromatogram of L-tyrosine, L-tryptophan and organic iodine in Example 1 of the present application; Figure 2 The HPLC chromatogram of the kelp powder hydrolyzate in Example 1 of the present application; Figure 3This is the working curve for quantitative analysis of organic iodine of amino acid derivatives in Example 2 of the present application. DETAILED DESCRIPTION

[0021] The following embodiments of the technical solution of the present application will be described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0023] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0024] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0025] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0026] Kelp is a well-known iodine-rich food that is both a medicine and food. The Compendium of Materia Medica states that "kelp can cure goiter (i.e. goiter) and other edema diseases, and has the function of resolving phlegm and dispersing knots"; the iodine in kelp is composed of organic iodine and inorganic iodine, and the iodine-containing amino acids in organic iodine account for more than 50%. In recent years, foods with kelp extract (organic iodine) as additives have received attention, so it is urgent to establish an accurate and rapid method for detecting the content of organic iodine in amino acid derivatives in kelp.

[0027] In order to solve the technical problem of accurately and quickly detecting the content of organic iodine in amino acid derivatives in kelp, the present application provides a method for detecting organic iodine in seaweed, wherein the high performance liquid chromatography analysis method established in the present application can quantitatively determine the amino acid derivative organic iodine in the sample, namely 3-iodo-L-tyrosine (MIT), 3,5-diiodo-L-tyrosine (DIT), triiodothyronine (T3) and thyroxine (T4), without being interfered by L-tyrosine, L-tryptophan and L-phenylalanine in the sample; the concentration of amino acid derivative organic iodine is in the range of 0.1-100 μg / mL, and shows a good linear relationship with the integrated area of ​​the chromatographic peak; according to the signal-to-noise ratio analysis of the spectrum, under the chromatographic analysis conditions, the detection limit of MIT and DIT is 0.5 ng, while the detection limit of T3 and T4 is 1.0 ng.

[0028] In a first aspect, the present application provides a method for detecting organic iodine in seaweed, comprising the following steps: S1. Sample pretreatment: drying, crushing and sieving the seaweed sample to obtain seaweed powder; S2. Preparation of test solution: the seaweed powder is hydrolyzed, concentrated, fixed to volume, and filtered to serve as the test solution; S3. Qualitative and quantitative analysis of organic iodine: prepare various organic iodine standard solutions, draw the standard solutions, inject into liquid chromatograph, record the relative retention time and peak area of ​​each organic iodine in the standard solutions; the HPLC conditions are: use C18 chromatographic column, 0.1% TFA aqueous solution as mobile phase A, acetonitrile as mobile phase B, gradient elution; detection wavelength is 280nm; The test solution is drawn in, injected into a liquid chromatograph, and a spectrum is obtained using the high performance liquid chromatography conditions. The organic iodine in the test solution is qualitatively analyzed according to the relative retention time of each organic iodine in the standard solution. A standard curve is established according to the peak area of ​​each organic iodine in the standard solution, and the organic iodine in the test solution is quantitatively analyzed according to the standard curve.

[0029] In the technical solution of the embodiment of the present application, the molecular structure of the amino acid derivative organic iodine is as follows:

[0030] Monoiodotyrosine (MIT) 3,5-diiodotyrosine (DIT)

[0031] Triiodothyronine (T3) Thyroxine (T4) Both 3-iodo-L-iodotyrosine and 3,5-diiodo-L-tyrosine contain a substituted benzene ring structure, while among the amino acids that make up proteins, only L-tyrosine, L-tryptophan and L-phenylalanine contain a substituted benzene ring structure. L-phenylalanine has no absorption peak at 280nm, so 280nm wavelength can be selected as the detection wavelength to prevent other amino acid components in kelp hydrolysate from interfering with the determination of organic iodine (MIT, DIT, T3 and T4).

[0032] Preferably, the hydrolysis comprises the following steps: heating the seaweed powder in a 5 mol / L NaOH solution for hydrolysis, the solid-liquid ratio of the seaweed powder to the NaOH solution being 1:(5-10), the heating temperature being 110°C, and filtering after hydrolysis for 12 hours to obtain a hydrolyzate.

[0033] Preferably, the concentration comprises the following steps: adding acid to the hydrolyzate to adjust the pH to 7-9, filtering to obtain a filtrate, passing the filtrate through an HLB solid phase extraction column, washing the solid phase column with distilled water, eluting the HLB extraction column with 10% methanol, and finally eluting the extraction column with methanol to obtain an eluate, and concentrating the eluate under reduced pressure to dryness to obtain a sample to be tested.

[0034] Preferably, the volume determination comprises the following steps: dissolving the sample to be tested in 0.4 mL of 0.005 mol / L NaOH solution, filtering through a 0.22 μm microporous filter membrane, and obtaining a test solution.

[0035] Preferably, in gradient elution, the volume ratio of mobile phase B in each time period is: 0-1 min, 20% mobile phase B; 1-15 min, 20%-50% mobile phase B; 15-30 min, 50%-80% mobile phase B; 30-35 min, 80%-20% mobile phase B.

[0036] Preferably, the C18 chromatographic column is an InertSustain AQ-C18 chromatographic column of 4.6×250 mm×5 μm.

[0037] Preferably, the column temperature of the chromatographic column is 30° C.; the flow rate of the eluent is 1 mL / min; and the injection volume is 10 μL.

[0038] Preferably, the organic iodine includes one or more of 3-iodo-L-tyrosine, 3,5-diiodo-L-tyrosine, triiodothyronine and thyroxine.

[0039] Preferably, the detection limit of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine is 0.5 ng, and the detection limit of triiodothyronine and thyroxine is 1.0 ng.

[0040] Preferably, in step S1, the drying temperature is 40-80° C., and the product is sieved through a 60-mesh sieve after being crushed.

[0041] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used without specifying the manufacturer are all conventional products that can be obtained commercially.

[0042] 1. Preparation method Example 1 A method for detecting organic iodine in seaweed comprises the following steps: S1. Sample pretreatment: The seaweed sample used in Example 1 is kelp (Laminaria japonicaAreschoug), which was collected from Weihai, Shandong. The kelp sample was washed with clean water to remove the surface attachments, cut into pieces, and placed in an oven to dry at 60°C. The dried kelp sample was crushed with a high-speed multifunctional crusher and passed through a 60-mesh sieve to obtain kelp powder.

[0043] S2. Preparation of test solution: Weigh 2g of kelp powder, add 5mol / L sodium hydroxide solution at a solid-liquid ratio of 1:5, hydrolyze in an oil bath at 110℃ for 12 hours, and filter. Adjust the pH of the filtrate to 8 with 6mol / L hydrochloric acid and filter with filter paper. Pass the filtrate through an HLB solid phase extraction column, wash the solid phase column with distilled water, elute the HLB extraction column with 10% methanol, and finally elute the extraction column with methanol. Concentrate the methanol elution part to dryness under reduced pressure, dissolve in 0.4mL 0.005M NaOH, pass through a 0.22μm microporous filter membrane, and transfer to an injection bottle to obtain the test solution for testing.

[0044] S3. Qualitative analysis of organic iodine in amino acid derivatives by HPLC Preparation of standard solution: Accurately weigh 0.1000 g of 3-iodo-L-tyrosine, 3,5-diiodo-L-tyrosine, triiodothyronine (T3), thyroxine (T4), L-tyrosine, L-tryptophan and L-phenylalanine standards, respectively dissolve them in 0.005 M NaOH solution, transfer to a 100 ml volumetric flask, dilute to 100 ml, and prepare a 0.1 mg / ml standard stock solution.

[0045] 3-iodo-L-tyrosine, 3,5-diiodo-L-tyrosine, T3, T4, L-tyrosine, L-tryptophan and L-phenylalanine standards were determined under the working conditions of the HPLC, and the working conditions of the HPLC were as follows: InertSustain AQ-C18 chromatographic column (4.6×250mm, 5μm); column temperature was 30℃; flow rate was 1mL / min; injection volume was 10μL; UV detector, detection wavelength was 280nm.

[0046] Mobile phase A was 0.1% TFA in water, and mobile phase B was acetonitrile.

[0047] Gradient elution was used, and the volume ratio of mobile phase B in each time period was: 0-1 min, 20% mobile phase B; 1-15 min, 20%-50% mobile phase B; 15-30 min, 50%-80% mobile phase B; 30-35 min, 80%-20% mobile phase B.

[0048] like Figure 1 As shown, at a detection wavelength of 280 nm, the peak order of the standard sample in the HPLC is L-tyrosine, L-tryptophan, 3-iodo-L-iodotyrosine, 3,5-diiodo-L-tyrosine, T3 and T4.

[0049] The relative retention times of each component in the reversed phase liquid chromatography column are: L-tyrosine: 3.857min; 3-iodo-L-iodotyrosine: 6.797min; L-tryptophan: 7.168min; 3,5-diiodo-L-tyrosine: 9.434min; T3: 16.506min; T4: 18.724min.

[0050] The above HPLC conditions were used to qualitatively analyze the organic iodine in the kelp sample. The chromatogram obtained is shown in Figure 2 ,according to Figure 1 From the chromatogram of the Chinese standard, it was preliminarily judged that the peak at the relative retention time of 6.73min was MIT, 9.49min was DIT, 16.57 was T3, and no T4 chromatographic peak was found.

[0051] Example 2 The steps of S1 sample pretreatment and S2 test solution preparation in Example 2 are the same as those in Example 1, except that: S3. Quantitative Analysis of Amino Acid Derivatives and Organic Iodine by HPLC (1) Preparation of standard organic iodine solution Accurately weigh 24.9 mg of MIT, 25.4 mg of DIT, 25.7 mg of T3, and 25.9 mg of T4, respectively, dissolve them in 0.005 M NaOH solution, make up to 100 mL, and prepare 249 μg / mL standard stock solution.

[0052] Take 4 mL of organic iodine standard solution and dilute it to 10 mL to prepare a 100 μg / mL standard solution; then, use the serial dilution method to prepare standard solutions with concentrations of 50 μg / mL, 10 μg / mL, 5 μg / mL, 1 μg / mL, 0.5 μg / mL, 0.1 μg / mL and 0.01 μg / mL.

[0053] (2) Draw the standard curve: Take the concentrations of organic iodine standard solutions as follows: 0.1μg / ml, 0.5μg / ml, 1μg / ml, 5μg / ml, 10μg / ml, 50μg / ml, 100μg / ml, and measure them according to the working conditions of the HPLC. Draw a standard curve with the mass of organic iodine as the abscissa and the corresponding peak area as the ordinate (see Figure 3 ).

[0054] HPLC working conditions: InertSustain AQ-C18 chromatographic column (4.6×250mm, 5μm); column temperature was 30℃; flow rate was 1mL / min; injection volume was 10μL; UV detector, detection wavelength was 280nm.

[0055] Mobile phase A was 0.1% TFA in water, and mobile phase B was acetonitrile.

[0056] Gradient elution was used, and the volume ratio of mobile phase B in each time period was: 0-1 min, 20% mobile phase B; 1-15 min, 20%-50% mobile phase B; 15-30 min, 50%-80% mobile phase B; 30-35 min, 80%-20% mobile phase B.

[0057] (3) Calculate the content of each organic iodine: aspirate the test solution, inject it into the liquid chromatograph, obtain the spectrum using high performance liquid chromatography conditions, calculate the peak area of ​​each organic iodine in the test solution, and obtain the concentration of the corresponding organic iodine according to the standard curve.

[0058] According to the above method, the contents of 3-iodo-L-tyrosine, 3,5-diiodo-L-tyrosine and triiodothyronine in kelp samples taken from Weihai, Shandong were measured to be 12.7 μg / g, 13.4 μg / g and 0.002 μg / g respectively.

[0059] The concentration of amino acid derivative organic iodine is in the range of 0.1-100 μg / mL, showing a good linear relationship with the integrated area of ​​the chromatographic peak; according to the signal-to-noise ratio analysis of the spectrum, under the chromatographic analysis conditions, the detection limit of MIT and DIT is 0.5 ng, while the detection limit of T3 and T4 is 1.0 ng.

[0060] Comparative Example 1 After cleaning the surface of commercially available dried kelp, dry it at 85°C, cut it into pieces and grind it into fine powder in a mortar. Weigh 0.5000g of kelp sample, add 50mL of methanol (6+4) solution, shake it overnight at 37°C at 150r / min on a shaker, filter it with filter paper, make the filtrate volume to 50mL, filter it with a 0.45μm microporous filter membrane, and measure it with a high-performance gas chromatograph. The steps are as follows: Standard curve drawing: 0.1g / L, weigh 10.0mg of 3,5-diiodotyrosine reference substance (purity not less than 98%) and place it in a 100mL volumetric flask, dissolve it with methanol (6+4) solution and dilute it to the scale, shake it well. Pipette 1, 5, 10, 15, 20μL of DIT standard solution, measure it according to the instrument working conditions, and draw a standard curve with the mass of DIT as the horizontal axis and the corresponding peak area as the vertical axis. The results show that the mass of DIT is linear in the range of 0.1~2μg, and the linear regression equation is y=1.524×105x+2.232×104. The detection limit of the method calculated by 3 times the baseline noise is 1.15ng.

[0061] A ZORBAX Eclipse XDB-C18 column (4.6 mm × 250 mm, 5 μm) was used; the column temperature was 30 °C; the flow rate was 0.5 mL / min; the detection wavelength was 312 nm; the detection time was 12 min; the injection volume was 10 μL. The mobile phase was a mixed solution of methanol and water (50 μL of triethanolamine and tetrahydrofuran were added to 500 mL of water) with a volume ratio of 25:75.

[0062] The kelp sample was measured according to the above steps, and the DIT content in the kelp sample was 0.5318 mg / g.

[0063] Comparative Example 1 is an organic iodine detection method in the prior art. It can be seen from Example 1 and Comparative Example 1 that the detection method of the present application can simultaneously detect four organic iodine compounds, namely 3-iodo-L-tyrosine, 3,5-diiodo-L-tyrosine, triiodothyronine, and thyroxine. The detection limits of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine in Example 1 of the present application are 0.5 ng, and the detection limits of triiodothyronine and thyroxine are 1.0 ng, which are much lower than 1.15 ng in Comparative Example 1, indicating that a higher detection accuracy can be obtained by using the detection method of the present application.

[0064] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and the same effect as the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for detecting organic iodine in seaweed, characterized in that: The steps include: S1. Sample pretreatment: drying, crushing and sieving the seaweed sample to obtain seaweed powder; S2. Preparation of test solution: the seaweed powder is hydrolyzed, concentrated, fixed to volume, and filtered to serve as the test solution; S3. Qualitative and quantitative analysis of organic iodine: prepare various organic iodine standard solutions, draw the standard solutions, inject into liquid chromatograph, record the relative retention time and peak area of ​​each organic iodine in the standard solutions; the HPLC conditions are: use C18 chromatographic column, 0.1% TFA aqueous solution as mobile phase A, acetonitrile as mobile phase B, gradient elution; detection wavelength is 280nm; The test solution is drawn and injected into a liquid chromatograph, a spectrum is obtained using the high performance liquid chromatography conditions, and a qualitative analysis of the organic iodine in the test solution is performed according to the relative retention time of each organic iodine in the standard solution; A standard curve was established according to the peak area of ​​each organic iodine in the standard solution, and the organic iodine in the test solution was quantitatively analyzed based on the standard curve.

2. The method for detecting organic iodine in seaweed according to claim 1, characterized in that: The hydrolysis comprises the following steps: heating the seaweed powder in a 5 mol / L NaOH solution for hydrolysis and filtering to obtain a hydrolyzate, wherein the solid-liquid ratio of the seaweed powder to the NaOH solution is 1:(5-10).

3. The method for detecting organic iodine in seaweed according to claim 2, characterized in that: The concentration comprises the following steps: adding acid to the hydrolyzate to adjust the pH to 7-9, filtering to obtain a filtrate, passing the filtrate through an HLB solid phase extraction column, washing the solid phase column with distilled water, eluting the HLB extraction column with 10% methanol, and finally eluting the extraction column with methanol to obtain an eluate, and concentrating the eluate under reduced pressure to dryness to obtain a sample to be tested.

4. The method for detecting organic iodine in seaweed according to claim 3, characterized in that: The volume determination comprises the following steps: dissolving the sample to be tested in 0.4 mL of 0.005 mol / L NaOH solution, filtering through a 0.22 μm microporous filter membrane, and obtaining a test solution.

5. The method for detecting organic iodine in seaweed according to claim 1, characterized in that: The steps of quantitative analysis of organic iodine are as follows: preparing organic iodine standard solutions of different concentrations, aspirating the standard solutions, injecting into a liquid chromatograph, recording the peak area of ​​the standard solutions, and drawing a standard curve with the mass of organic iodine as the abscissa and the corresponding peak area as the ordinate; The test solution is drawn and injected into a liquid chromatograph, a spectrum is obtained using the high performance liquid chromatography conditions, the peak area of ​​each organic iodine in the test solution is calculated, and the concentration of the corresponding organic iodine is obtained according to the standard curve.

6. The method for detecting organic iodine in seaweed according to claim 1, characterized in that: In the gradient elution, the volume ratio of mobile phase B in each time period is: 0-1 min, 20% mobile phase B; 1-15 min, 20%-50% mobile phase B; 15-30 min, 50%-80% mobile phase B; 30-35 min, 80%-20% mobile phase B.

7. The method for detecting organic iodine in seaweed according to claim 1, characterized in that: The C18 chromatographic column is an InertSustain AQ-C18 chromatographic column of 4.6×250 mm×5 μm.

8. The method for detecting organic iodine in seaweed according to claim 1, characterized in that: The column temperature of the chromatographic column is 30° C.; the flow rate of the eluent is 1 mL / min; and the injection volume is 10 μL.

9. The method for detecting organic iodine in seaweed according to claim 1, characterized in that: The organic iodine includes one or more of 3-iodo-L-tyrosine, 3,5-diiodo-L-tyrosine, triiodothyronine and thyroxine.

10. The method for detecting organic iodine in seaweed according to claim 9, characterized in that: The detection limits of the 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine are 0.5 ng, and the detection limits of the triiodothyronine and thyroxine are 1.0 ng.

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