Method for determination of organic iodine in edible salt by ultra performance liquid chromatography-tandem mass spectrometry

Abstract

This invention belongs to the field of organic iodine detection technology and discloses a method for determining organic iodine in edible salt using ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS / MS). The method includes the following steps: 1) dissolving edible salt in water to obtain a first solution; 2) loading the first solution onto an HLB solid-phase extraction column, and after adsorption, eluting with methanol-water solution followed by methanol elution, filtering the eluent to obtain a second solution; 3) determining the organic iodine in the second solution using UHPLC-MS / MS, and then calculating the organic iodine content in the edible salt. The UHPLC uses a 0.1%–0.12% (v / v) formic acid aqueous solution as mobile phase A and methanol as mobile phase B for gradient elution. This invention can efficiently and accurately determine the organic iodine content in edible salt, with advantages such as high detection sensitivity, strong specificity, no loss of target analytes, and short analysis cycle. The detection limits for 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine are both as low as 1 μg / kg, and the quantitation limits are both as low as 2 μg / kg.

Description

Technical Field

[0001] This invention belongs to the field of organic iodine detection technology, specifically relating to a method for determining organic iodine in edible salt by ultra-high performance liquid chromatography-tandem mass spectrometry. Background Technology

[0002] Rational control of iodine content in table salt is of great significance for safeguarding public health. Traditional table salt primarily uses inorganic iodine (such as potassium iodate or potassium iodide) as its main iodine source. In recent years, organic iodine has gradually entered the market as a novel iodine source. 3-Iodo-L-tyrosine (MIT) and 3,5-diiodo-L-tyrosine (DIT) are common forms of organic iodine in table salt. Compared with inorganic iodine, organic iodine has higher stability and bioavailability, thus playing a more sustained and effective role in the human body, and possesses broad market development potential. Although the health benefits of organic iodine are gradually gaining attention, the lack of unified and scientific testing methods in the market has prevented standardized management of the organic iodine content in table salt. This issue not only affects the quality assurance of related products but also limits the promotion and regulation of organic iodized salt products.

[0003] Currently, the main methods for detecting and analyzing organic iodine include titration, amino acid analysis, gas chromatography, and ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS / MS). Among these, titration can only determine the total iodine content in a sample, cannot distinguish between organic and inorganic iodine, and cannot perform qualitative and quantitative analysis of single organic iodine compounds; furthermore, its detection sensitivity is low. Amino acid analysis, lacking mass spectrometry for qualitative analysis, is prone to false positives, and its sensitivity, separation speed, and linear range are all relatively low, making it difficult to meet the need for simultaneous detection of multiple iodoamino acids in complex matrices. Gas chromatography struggles to simultaneously determine multiple organic iodine compounds with significant polarity differences, and its qualitative ability is relatively weak, also prone to false positives. In comparison, UPLC-MS / MS combines the high separation efficiency of liquid chromatography with the high sensitivity of mass spectrometry, making it more suitable for the detection of organic iodine. Researchers have used UPLC-MS / MS to detect organic iodine in other substances, but there are still problems such as poor detection precision, insufficient sensitivity, complex pretreatment, and low detection efficiency. It is difficult to achieve accurate determination of specific organic iodine or trace organic iodine. In addition, some methods require special pretreatment such as high temperature, which is not suitable for high-salt matrix samples.

[0004] As an indispensable condiment in daily diet, the accurate detection of organic iodine content in table salt is of great significance for food safety and quality supervision. However, current technology lacks a detection method suitable for high-salt and complex matrices like table salt, which features simple pretreatment procedures, high detection sensitivity, good repeatability, and accurate determination of specific organic iodine targets. Therefore, it is urgent to optimize existing detection and pretreatment technologies and establish an efficient and reliable detection method for organic iodine in table salt to meet the actual needs of testing and quality supervision of table salt and related products. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for determining organic iodine in edible salt by ultra-high performance liquid chromatography-tandem mass spectrometry, which can efficiently and accurately determine the organic iodine content in edible salt and has the advantages of high detection sensitivity, strong specificity and short analysis cycle.

[0006] To address the technical problem proposed in this invention, this invention provides a method for determining organic iodine in edible salt using ultra-high performance liquid chromatography-tandem mass spectrometry, comprising the following steps: 1) Dissolve table salt in water to obtain the first solution; 2) The first solution is loaded onto an HLB solid-phase extraction column for adsorption and elution. The eluent is then filtered to obtain the second solution. 3) The organic iodine content in the second solution was detected by ultra-high performance liquid chromatography-tandem mass spectrometry.

[0007] In the above scheme, the organic iodine includes one or both of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine.

[0008] In the above scheme, the mass ratio of the edible salt to the volume ratio of the dissolving water is 2g:(5~10)mL.

[0009] In the above scheme, the packing material used in the HLB solid phase extraction column is a hydrophilic-lipophilic balanced copolymer of N-vinylpyrrolidone and divinylbenzene, with a packing amount of 200~500 mg.

[0010] In the above scheme, water is added to the HLB solid-phase extraction column before use to activate the packing material inside the column. Furthermore, the amount of water used for activation is 50% to 85% of the HLB solid-phase extraction column volume.

[0011] In the above scheme, the first solution is loaded onto an HLB solid-phase extraction column. After adsorption, it is sequentially eluted with a methanol-water solution and then eluted with methanol, and the eluent is collected. Further, the volume fraction of the methanol-water solution used for elution is ≤10%, and the amount added is 50%~85% of the volume of the HLB solid-phase extraction column; the amount of methanol used for elution is 65%~85% of the volume of the HLB solid-phase extraction column.

[0012] In the above scheme, the eluent filtration uses a hydrophilic PTFE filter membrane with a pore size ≤0.22μm.

[0013] In the above scheme, the conditions for ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS / MS) are as follows: using a C18 column, with a mobile phase of 0.1%~0.12% formic acid aqueous solution as mobile phase A and methanol as mobile phase B, and performing gradient elution.

[0014] Furthermore, the column temperature of the chromatographic column is 35~40℃, the flow rate is 0.2~0.3mL / min, and the injection volume is 1~2μL.

[0015] Furthermore, in the gradient elution, the volume ratio of mobile phase B in each time period is as follows: 0~1 min, 10%, with the remainder being mobile phase A, the same below; 1~2.5 min, 10%~40%; 2.5~4 min, 40%; 4~5 min, 40%~90%; 5~5.1 min, 90%; 5.1~10 min, 90%~10%.

[0016] In the above scheme, the mass spectrometry conditions in the ultra-high performance liquid chromatography-tandem mass spectrometry detection are as follows: adopting electrospray ionization source negative ion mode and multiple reaction monitoring mode, ion source temperature is 140~150 ℃, desolvation gas temperature is 300~320℃, capillary voltage is 2.4~2.5 kV, and desolvation gas flow rate is 650~700 L / h.

[0017] Furthermore, the qualitative detection ion pair for 3-iodo-L-tyrosine was 306.0 / 134.1, the cone voltage was 36~40V, and the collision energy was 20~24V.

[0018] Furthermore, the quantitative detection ion pair for 3-iodo-L-tyrosine was 306.0 / 127.0, the cone voltage was 36~40V, and the collision energy was 16~20V.

[0019] Furthermore, the qualitative detection ion pair for 3,5-diiodo-L-tyrosine was 432.0 / 371.0, the cone voltage was 40~44V, and the collision energy was 22~26V.

[0020] Furthermore, the quantitative detection ion pair for 3,5-diiodo-L-tyrosine was 432.0 / 127.0, the cone voltage was 40~44V, and the collision energy was 36~40V.

[0021] The method of this invention has a detection limit of as low as 1 μg / kg and a quantification limit of as low as 2 μg / kg for 3-iodo-L-tyrosine.

[0022] The method of this invention has a detection limit of as low as 1 μg / kg and a quantification limit of as low as 2 μg / kg for 3,5-diiodo-L-tyrosine.

[0023] Compared with the prior art, the beneficial effects of the present invention are: This invention addresses the high-salt matrix characteristics of edible salt by developing a proprietary pretreatment method for extracting iodotyrosine using an HLB solid-phase extraction column. This method effectively enriches and extracts target compounds (3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine) from edible salt samples while efficiently removing high levels of inorganic salts and other interfering substances. It solves the problems of existing pretreatment methods being unsuitable for edible salt matrices, having low target compound extraction efficiency, and incomplete interference removal, thus laying a solid foundation for subsequent accurate detection.

[0024] This invention significantly shortens the elution time and improves the detection efficiency by optimizing the extraction and chromatographic separation procedures for iodotyrosine. It also reduces the loss of target analytes during elution, further ensuring the accuracy and repeatability of the detection results. This addresses the shortcomings of existing technologies, such as long elution times, low efficiency, and easy loss of target analytes, resulting in higher detection sensitivity and precision. The detection limit for 3-iodo-L-tyrosine is as low as 1 μg / kg, and the quantitation limit is as low as 2 μg / kg; the detection limit for 3,5-diiodo-L-tyrosine is as low as 1 μg / kg, and the quantitation limit is as low as 2 μg / kg. Attached Figure Description

[0025] Figure 1 The total ion chromatograms are for Example 1 (A), Comparative Example 1-1 (B), Comparative Example 1-2 (C) and Comparative Example 1-3 (D).

[0026] Figure 2 The total ion flow chromatograms are for Comparative Example 2-1 (A), Example 1 (B), Comparative Example 2-2 (C), and Comparative Example 2-3 (D).

[0027] Figure 3 The total ion flow chromatograms are for Example 1 (A), Comparative Example 3-1 (B), and Comparative Example 3-1 (C).

[0028] Figure 4 The bar chart shows the recovery rates of Example 1 and Comparative Examples 4-1, 4-2, and 4-3.

[0029] Figure 5 The bar chart shows the recovery rates of Example 1 and Comparative Examples 5-1, 5-2, 5-3, 5-4, and 5-5.

[0030] Figure 6 The bar chart shows the recovery rates of Example 1 and Comparative Examples 6-1, 6-2, and 6-3. Detailed Implementation

[0031] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0032] Example 1 A method for determining organic iodine in edible salt by ultra-high performance liquid chromatography-tandem mass spectrometry specifically includes the following steps: (1) Solution preparation Weigh 2g of salt, add 6mL of purified water, dissolve and mix well to obtain the first solution.

[0033] (2) Sample pretreatment A 6 mL HLB solid-phase extraction column packed with 200 mg of a hydrophilic-lipophilic balanced copolymer of N-vinylpyrrolidone and divinylbenzene (Poly-Sery HLB Pro, CNW, China) was activated with 3 mL of ultrapure water. After activation, the first solution was quickly loaded onto the column. After the solution had flowed out naturally, 4 mL of 5% (v / v) methanol aqueous solution was added for elution, and the eluent was discarded. After the eluent had completely flowed out, 4 mL of methanol was used for elution, and the eluent was collected. The resulting eluent was filtered through a 0.22 μm hydrophilic PTFE syringe filter to obtain the second solution, which was then transferred to a vial for analysis.

[0034] (3) Sample testing The second solution and the standard solution after the same pretreatment were separately sent to UPLC-MS for collection and analysis.

[0035] The conditions for ultra-high performance liquid chromatography were as follows: column: ACQUITY UPLC BEH C18 (2.1×50 mm, 1.7 μm, Waters Corporation, USA); column temperature: 35~40℃; flow rate: 0.2 mL / min; mobile phase A: 0.1% formic acid aqueous solution; mobile phase B: methanol; gradient elution program is shown in Table 1.

[0036] The mass spectrometry conditions were as follows: negative ion mode and multiple reaction monitoring mode were used with electrospray ionization source, ion source temperature was 150℃, desolvation gas temperature was 300℃, capillary voltage was 2.4kV, desolvation gas flow rate was 650L / h, and ion pair information is shown in Table 2.

[0037] Table 1

[0038] Table 2

[0039] * indicates quantitative ions (4) Calculation of results The analytical results of the standard solution by UPLC-MS were collected. A standard curve was plotted with the peak area of ​​the target organic iodine as the ordinate and the corresponding concentration of the target organic iodine as the abscissa, as shown in Table 3. The peak area of ​​the target organic iodine in the second solution was then substituted into the standard curve to calculate the concentration of the target organic iodine in the second solution. Based on the dilution factor and sample weight during sample pretreatment, the content of the target organic iodine in the salt was calculated. The LOD and LOQ were calculated using a signal-to-noise ratio of 3 and 10, respectively. The LOD for both MIT and DIT was 1 μg / kg, and the LOQ was 2 μg / kg, indicating that the method has good sensitivity.

[0040] Table 3

[0041] The calculated MIT and DIT contents in the salt sample of this embodiment were 103.2 μg / kg and 105.1 μg / kg, respectively.

[0042] Example 2 To examine the accuracy of the method for detecting organic iodine in table salt provided by this invention, a spike recovery experiment was conducted. Spike recovery tests and precision were performed at three concentration levels: low, medium, and high. To ensure the reliability and accuracy of the data, each concentration level was measured independently six times. The specific steps were as follows: add the standard to 6 mL of purified water, perform sample pretreatment according to step (2) of Example 1, and perform the measurement according to step (3), repeating the measurement six times.

[0043] According to the experimental results, when the spiked concentration ranged from 10 to 200 μg / kg, the average recovery rate was 88% to 97.3%, and the inter-day and intra-day relative standard deviations were both less than 0.1%, indicating that the accuracy and precision of the method met the requirements of analytical techniques. The specific results of the average recovery rate and relative standard deviation are shown in Table 4.

[0044] Table 4

[0045] Comparative Example 1 The mobile phase used in ultra-high performance liquid chromatography (UHPLC) in this invention plays a crucial role in the accuracy of the detection results. In liquid chromatography-mass spectrometry (LC-MS), the composition of the mobile phase is a significant factor affecting the ionization efficiency of compounds and the separation effect of chromatographic peaks. The composition of the mobile phase directly influences the ionization efficiency, chromatographic retention behavior, and matrix effect of the analyte. Different mobile phase systems exhibit fundamental differences in separation capability, peak shape symmetry, and response intensity. The only difference between this comparative example and Example 1 is the mobile phase used in UHPLC. Three comparative examples, 1-1, 1-2, and 1-3, were set up: in Comparative Example 1-1, water was used as mobile phase A and methanol as mobile phase B; in Comparative Example 1-2, a 0.1% (v / v) formic acid aqueous solution was used as mobile phase A and acetonitrile as mobile phase B; and in Comparative Example 1-3, a 5 mmol / L ammonium formate buffer solution was used as mobile phase A and methanol as mobile phase B. Figure 1 As can be seen, the three mobile phase combinations in the comparative examples all exhibited varying degrees of peak broadening, tailing, or reduced response. However, when Example 1 used a 0.1% formic acid aqueous solution-methanol system, the target substance had a sharp and symmetrical peak shape, the highest response, and the best separation effect. This effectively improved the chromatographic retention behavior and mass spectrometry ionization efficiency, ensuring the accuracy, reproducibility, and sensitivity of the detection results.

[0046] Comparative Example 2 In this invention, the injection volume of ultra-high performance liquid chromatography (UHPLC) plays a crucial role in ensuring the accuracy of the detection results. The injection volume, by altering the column loading, directly affects the peak shape, resolution, and response intensity of the target analyte. An appropriate injection volume not only improves analytical sensitivity but also avoids peak shape distortion caused by column overload or solvent effects, thereby ensuring good separation. The only difference between this comparative example and Example 1 is the injection volume of the UHPLC. Three comparative examples, 2-1, 2-2, and 2-3, were set up: the injection volume for Comparative Example 2-1 was 1 μL, for Comparative Example 2-2 it was 5 μL, and for Comparative Example 2-3 it was 10 μL. Figure 2 As can be seen, when the injection volume is 1-2 μL, the target analyte peaks are sharp and well-separated, effectively avoiding peak overlap or excessive broadening. With further increases in injection volume, the methanol elution capacity of the dissolved sample is stronger than that of the mobile phase, leading to peak bifurcation due to the solvent effect. Volumes of 5 μL and above show peak broadening or distortion. Therefore, an injection volume of 1-2 μL is considered the optimal choice in this invention, achieving the best balance between sensitivity and separation, ensuring accurate and reliable detection results.

[0047] Comparative Example 3 In this invention, the flow rate of ultra-high performance liquid chromatography (UHPLC) is a key parameter for balancing analysis time and resolution, controlling column efficiency and column pressure, and ensuring optimal performance of the chromatographic and mass spectrometric systems. Changes in flow rate can directly alter the retention behavior, separation efficiency, and response intensity of the target analyte, thereby affecting the detection results. The only difference between this comparative example and Example 1 is the flow rate of the UHPLC. Two comparative examples, Comparative Example 3-1 and Comparative Example 3-2, were set up: the flow rate of Comparative Example 3-1 was 0.3 mL / min, and the flow rate of Comparative Example 3-2 was 0.4 mL / min. Figure 3 As can be seen, at a lower flow rate of 0.2–0.3 mL / min, the target analyte exhibits sharp peaks, good separation, and no significant impurity interference, demonstrating excellent detection performance. However, when the flow rate is further increased to 0.4 mL / min, peak broadening, reduced response, and exacerbated impurity interference occur. This indicates that 0.2–0.3 mL / min is the optimal flow rate, achieving the best balance between sensitivity, separation, and detection efficiency, ensuring accurate detection of the target analyte.

[0048] Comparative Example 4 In this invention, an HLB solid-phase extraction column is used for sample pretreatment. When the sample passes through the solid-phase extraction column, the target compound interacts with the adsorbent inside the column and is effectively captured. However, actual samples often contain other matrix components, which may not only interfere with the separation and detection of the target compound but also affect the lifespan of the chromatographic column. Therefore, the selection of the eluent is crucial. The only difference between this comparative example and Example 1 is the eluent after adsorption by the HLB solid-phase extraction column. Three comparative examples, 4-1, 4-2, and 4-3, are set up: Comparative example 4-1 is eluented with pure water, Comparative example 4-2 is eluented with a 10% (v / v) methanol-water solution, and Comparative example 4-3 is eluented with a 15% (v / v) methanol-water solution.

[0049] Comparative Example 4-1 showed that the contents of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine in the edible salt sample of Example 1 were 110.36 μg / kg and 72.20 μg / kg, respectively; Comparative Example 4-2 showed that the contents of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine in the edible salt sample of Example 1 were 92.49 μg / kg and 90.82 μg / kg, respectively; Comparative Example 4-3 showed that the contents of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine in the edible salt sample of Example 1 were 96.69 μg / kg and 60.89 μg / kg, respectively.

[0050] The test results of Comparative Examples 4-1 and 4-3 differed significantly from those of Example 1. This was because the change in the proportion of methanol in the elution solvent directly altered the solvent polarity and elution capacity, thereby affecting the impurity removal efficiency and the recovery rate of organic iodine. Figure 4The bar chart shows the recovery rates of Example 1 and the three comparative examples. It can be seen that using methanol aqueous solution with a volume fraction of ≤10% as the elution solvent can effectively remove impurities while keeping the recovery rates of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine within the acceptable range of 70% to 120%. It is the optimal elution solvent to ensure accurate and reliable test results.

[0051] Comparative Example 5 In this invention, the selection of the elution solvent for the HLB solid-phase extraction column is also crucial in the solid-phase extraction process, directly determining the efficiency of the desorption of the target compound from the adsorbent and the accuracy of subsequent analysis. The only difference between this comparative example and Example 1 is the elution solvent after adsorption by the HLB solid-phase extraction column. Five comparative examples were set up: Comparative example 5-1 used a 40% (v / v) methanol-water solution for elution; Comparative example 5-2 used a 50% (v / v) methanol-water solution for elution; Comparative example 5-3 used a 60% (v / v) methanol-water solution for elution; Comparative example 5-4 used a 70% (v / v) methanol-water solution for elution; and Comparative example 5-5 used an 80% (v / v) methanol-water solution for elution.

[0052] Comparative Example 5-1 showed that the contents of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine in the edible salt sample of Example 1 were 79.50 μg / kg and 67.06 μg / kg, respectively; Comparative Example 5-2 showed that the contents of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine in the edible salt sample of Example 1 were 98.14 μg / kg and 67.82 μg / kg, respectively; Comparative Example 5-3 showed that the contents of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine in the edible salt sample of Example 1 were 91.70 μg / kg and 67.82 μg / kg, respectively; and Comparative Example 5-4 showed that the contents of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine in the edible salt sample of Example 1 were 95.17 μg / kg and 67.84 μg / kg, respectively. The contents of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine in the edible salt sample of Example 1 were measured to be 89.70 μg / kg and 62.54 μg / kg, respectively, in Comparative Examples 5-5.

[0053] The test results above differed significantly from those in Example 1 because the proportion of methanol in the elution solvent directly affected the elution capacity, thereby altering the elution efficiency and recovery rate of the target compounds (3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine). Figure 5The bar chart shows the recovery rates of Example 1 and the five comparative groups. It can be seen that as the methanol content increases, the recovery rate of 3,5-diiodo-L-tyrosine gradually increases, and the recovery rate of 3-iodo-L-tyrosine remains stable within the acceptable range. The 100% methanol group (Example 1) showed the highest target analyte recovery rate, and all results met the requirements. This indicates that using pure methanol as the elution solvent can achieve sufficient elution of the target analyte, making it the optimal elution solvent for ensuring accurate and reliable detection results.

[0054] Comparative Example 6 In this invention, the volume of the elution solvent in the HLB solid-phase extraction column is also a crucial factor affecting the recovery rate and analytical efficiency of the target compound during the solid-phase extraction process. During elution, if the volume of the elution solvent is too small, the target compound may not be completely desorbed from the solid material, thus reducing the recovery rate and affecting the accuracy of the experiment. Conversely, if the volume of the elution solvent is too large, while ensuring complete elution of the target compound, it will dilute the concentration of the target compound, which is detrimental to subsequent quantitative analysis. The only difference between this comparative example and Example 1 is the amount of elution solvent added after adsorption by the HLB solid-phase extraction column. Three comparative examples, 6-1, 6-2, and 6-3, were set up: 1 mL was added in Comparative Example 6-1, 2 mL in Comparative Example 6-2, and 3 mL in Comparative Example 6-3, corresponding to 17%, 33%, and 50% of the HLB solid-phase extraction column volume, respectively.

[0055] Comparative Example 6-1 showed that the contents of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine in the edible salt sample of Example 1 were 1.51 μg / kg and 2.82 μg / kg, respectively; Comparative Example 6-2 showed that the contents of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine in the edible salt sample of Example 1 were 241.94 μg / kg and 171.22 μg / kg, respectively; Comparative Example 6-3 showed that the contents of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine in the edible salt sample of Example 1 were 166.32 μg / kg and 125.01 μg / kg, respectively.

[0056] The above test results differ significantly from those in Example 1 because the volume of the elution solvent directly affects the elution efficiency of the target analyte and the degree of co-elution of impurities, which in turn determines the recovery rate and detection accuracy. Figure 6The bar chart shows the recovery rates of Example 1 and the three comparative examples. It can be seen that: Comparative Example 6-1 had insufficient elution, resulting in extremely low recovery; Comparative Examples 6-2 and 6-3 both had recovery rates exceeding the acceptable range of 70%–120% due to their elution volumes, failing to meet the accuracy requirements for quantitative analysis. In contrast, Example 1 used elution solvent volumes within the range of 65%–85% of the HLB solid-phase extraction column volume, controlling the recovery rate within the acceptable range. The extraction rates of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine both reached the ideal range of 70%–120%, ensuring both high recovery rates and effectively avoiding the dilution effect caused by excessive elution solvent. This ensures the accuracy and reliability of the target analyte detection results.

[0057] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for determining organic iodine in edible salt by ultra-high performance liquid chromatography-tandem mass spectrometry, characterized in that, Includes the following steps: 1) Dissolve table salt in water to obtain the first solution; 2) Load the first solution onto the HLB solid-phase extraction column. After adsorption is complete, wash with methanol-water solution and elute with methanol in sequence. Filter the eluent to obtain the second solution. 3) The organic iodine in the second solution was determined by ultra-high performance liquid chromatography-tandem mass spectrometry, and the organic iodine content in the edible salt was calculated. The ultra-high performance liquid chromatography used a gradient elution with a mobile phase of 0.1%~0.12% formic acid aqueous solution as mobile phase A and methanol as mobile phase B.

2. The method for determining organic iodine in edible salt by ultra-high performance liquid chromatography-tandem mass spectrometry according to claim 1, characterized in that, In the gradient elution, the volume ratio of mobile phase B in each time period is as follows: 0~1 min, 10%; 1~2.5 min, 10%~40%; 2.5~4 min, 40%; 4~5 min, 40%~90%; 5~5.1 min, 90%. 5.1~10 min, 90%~10%.

3. The method for determining organic iodine in edible salt by ultra-high performance liquid chromatography-tandem mass spectrometry according to claim 1, characterized in that, The ultra-high performance liquid chromatography uses a C18 column with a column temperature of 35~40℃ and a flow rate of 0.2~0.3mL / min.

4. The method for determining organic iodine in edible salt by ultra-high performance liquid chromatography-tandem mass spectrometry according to claim 1, characterized in that, The mass spectrometry conditions are as follows: an electrospray ionization source in negative ion mode and multiple reaction monitoring mode are adopted, the ion source temperature is 140~150 ℃, the desolvation gas temperature is 300~320 ℃, the capillary voltage is 2.4~2.5 kV, and the desolvation gas flow rate is 650~700 L / h.

5. The method for determining organic iodine in edible salt by ultra-high performance liquid chromatography-tandem mass spectrometry according to claim 1, characterized in that, The organic iodine is one or both of 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine.

6. The method for determining organic iodine in edible salt by ultra-high performance liquid chromatography-tandem mass spectrometry according to claim 1, characterized in that, For qualitative detection of 3-iodo-L-tyrosine, the monitoring ion pair for mass spectrometry is 306.0 / 134.1, the cone voltage is 36–40 V, and the collision energy is 20–24 V. For quantitative detection, the monitoring ion pair is 306.0 / 127.0, the cone voltage is 36–40 V, and the collision energy is 16–20 V. The detection limit for 3-iodo-L-tyrosine is as low as 1 μg / kg, and the quantitation limit is as low as 2 μg / kg.

7. The method for determining organic iodine in edible salt by ultra-high performance liquid chromatography-tandem mass spectrometry according to claim 1, characterized in that, For qualitative detection of 3,5-diiodo-L-tyrosine, the monitoring ion pair for mass spectrometry was 432.0 / 371.0, the cone voltage was 40–44 V, and the collision energy was 22–26 V. For quantitative detection, the monitoring ion pair was 432.0 / 127.0, the cone voltage was 40–44 V, and the collision energy was 36–40 V. The detection limit for 3,5-diiodo-L-tyrosine was as low as 1 μg / kg, and the quantitation limit was as low as 2 μg / kg.

8. The method for determining organic iodine in edible salt by ultra-high performance liquid chromatography-tandem mass spectrometry according to claim 1, characterized in that, The volume fraction of the methanol aqueous solution used for elution is ≤10%, and the amount added is 50%~85% of the HLB solid phase extraction column volume; the amount of methanol used for elution is 65%~85% of the HLB solid phase extraction column volume.

9. The method for determining organic iodine in edible salt by ultra-high performance liquid chromatography-tandem mass spectrometry according to claim 1, characterized in that, The packing material used in the HLB solid-phase extraction column is a hydrophilic-lipophilic balanced copolymer of N-vinylpyrrolidone and divinylbenzene, with a packing amount of 200~500 mg. Before use, water is added to the HLB solid-phase extraction column to activate the packing material inside the column. The amount of water used for activation is 50%~85% of the volume of the HLB solid-phase extraction column.

10. The method for determining organic iodine in edible salt by ultra-high performance liquid chromatography-tandem mass spectrometry according to claim 1, characterized in that, The mass ratio of the edible salt to the volume ratio of the water used for dissolving it is 2g:(5~10)mL; the eluent is filtered using a hydrophilic PTFE membrane with a pore size ≤0.22μm.

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