Method for determining iodide in domestic drinking water

Abstract

The invention belongs to the technical field of separation and detection, and particularly relates to a method for determining iodide in domestic drinking water. Measuring the iodide in the domestic drinking water by adopting a high performance liquid chromatography-ultraviolet detection method; taking a domestic drinking water sample solution for detection, and quantifying by an external standard method; according to the detection method, a Metrosep A Supp5-250 chromatographic column (250 mm * 4.0 mm, 5 [mu] m) is adopted for separation, 4.5 mmol / L Na2CO3, 1.0 mmol / L NaHCO3 and 35% acetonitrile are adopted as a mobile phase, a DAD detector is adopted, the wavelength is 226 nm, the flow rate is 0.60 mL / min, and the column temperature is 50 DEG C. The invention also discloses a method for detecting the content of the sodium hydroxide in the sample. According to methodology verification, the method can be used for measuring iodide in domestic drinking water, the detection limit is 2.0 mu g / L and is superior to that of a spectrophotometric method and a volumetric method in the national standard, no complex pretreatment process exists, specificity is high, toxic and harmful chemical reagents are not used, online automatic sample injection can be achieved, and the method has obvious advantages for large-batch samples; compared with inductively coupled plasma mass spectrometry, used instruments are relatively cheap, and basic popularization and application are facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of separation and detection, and specifically relates to a method for determining iodide in domestic drinking water. Background Art

[0002] Iodine is one of the essential trace elements for the human body. At different stages of human growth and development, iodine deficiency or iodine excess can cause health damage. Iodine deficiency leads to brain development disorders in infants and young children, goiter in adults, and can also cause miscarriage, premature birth, stillbirth, and congenital malformations. Iodine excess can cause latent autoimmune thyroid diseases to turn into overt diseases, resulting in thyroid diseases such as hyperthyroidism. The intake of iodine by the human body mainly comes from food and domestic drinking water. In the natural environment, iodine mainly exists in the form of iodide and exists in ionic form in water. The "Hygiene Standards for Domestic Drinking Water" promulgated in 2022 also includes iodide in the reference indicators of domestic drinking water quality. Therefore, it is necessary to monitor iodide in domestic drinking water.

[0003] At present, the main methods for determining iodide include spectrophotometry, enzyme immunoassay, iodine electrode method, ion chromatography, high performance liquid chromatography, gas chromatography, inductively coupled plasma mass spectrometry. Some of these methods have complex operations, some use highly toxic reagents and cannot achieve online automation, some have insufficient specificity, some have harsh conditions, some have insufficiently low detection limits, and some have expensive instruments, which are not conducive to popularization and application at the grass-roots level. Therefore, there is an urgent need to establish a method with simple operation, strong specificity, high sensitivity, capable of online automatic sampling, having obvious advantages for a large number of samples, and using relatively inexpensive instruments. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention discloses a method for determining iodide in domestic drinking water using a high performance liquid chromatograph, adopting the principle of ion exchange and ultraviolet detection method, with simple operation, strong specificity, high sensitivity, capable of online automatic sampling for a large number of samples, and being conducive to grass-roots promotion and application.

[0005] The method for determining iodide in domestic drinking water according to the present invention is as follows:

[0006] The iodide in drinking water is determined by high performance liquid chromatography - ultraviolet detection method; the drinking water sample solution is taken for detection, and the external standard method is used for quantification; the detection method is as follows: separation is carried out using a Metrosep A Supp5 - 250 chromatographic column (250 mm × 4.0 mm, 5 μm), with 4.5 mmol / L Na2CO3 + 1.0 mmol / L NaHCO3 + 5% acetone as the mobile phase, or 4.5 mmol / L Na2CO3 + 1.0 mmol / L NaHCO3 + 0% - 35% acetonitrile as the mobile phase, the flow rate is 0.50 - 1.20 mL / min, and the column temperature is 25 - 60 °C.

[0007] Preferably, the drinking water sample solution is passed through a 0.45 μm microporous filter membrane and directly detected on the machine.

[0008] The ultraviolet detection uses a DAD detector. The ultraviolet detection wavelength is 226 nm. The flow rate is 0.60 mL / min. The column temperature is 50 °C.

[0009] Preferably, the mobile phase is 4.5 mmol / L Na2CO3 + 1.0 mmol / L NaHCO3 + 0% - 35% acetonitrile. More preferably, the mobile phase is 4.5 mmol / L Na2CO3 + 1.0 mmol / L NaHCO3 + 35% acetonitrile.

[0010] The drinking water sample is purified water or tap water or mineral water or well water.

[0011] Application of the above - mentioned method in the determination of iodide in drinking water.

[0012] Technical effects: (1) By using a high - performance liquid chromatograph, the present invention adopts the principle of ion exchange and the method of diode array detection, selects a suitable chromatographic column and detection wavelength, and optimizes the mobile phase, the flow rate of the mobile phase and the column temperature, and comprehensively establishes a high - performance liquid - ion exchange chromatography method for determining iodide in drinking water. The results of methodological evaluation and verification show that the content of iodide in 4 kinds of drinking water, namely purified water, tap water, mineral water and well water, can be determined by using the method of the present invention. (2) The detection limit of the detection method of the present invention is 2.0 μg / L, which is better than the spectrophotometry and volumetric method in the national standard. Moreover, the sample is directly filtered through the membrane and detected on the machine without complex pretreatment process, with good accuracy, precision and stability, strong specificity, without using toxic and harmful chemical reagents, and can realize online automatic injection, having obvious advantages for a large number of samples; compared with inductively coupled plasma mass spectrometry, the instrument used is relatively cheap, which is conducive to popularization and application at the grass - roots level. Description of the Drawings

[0013] Figure 1 It is the ultraviolet spectrum of iodide ion;

[0014] Figure 2 It is the exclusive chromatogram of several kinds of domestic drinking water: among which, a is the reference solution, b is pure water, c is tap water, d is mineral water, and e is well water. Detailed implementation manners

[0015] Example 1: Description and exploration of the method of the present invention

[0016] 1 Experimental materials and methods

[0017] 1.1 Instruments, reagents and materials

[0018] Agilent 1200 high performance liquid chromatograph (Agilent Technologies, USA); Milli-Q ultrapure water machine (Millipore Corporation, USA). Acetonitrile (chromatographic grade, Merck KGaA, Germany); acetone (chromatographic grade, Sinopharm Chemical Reagent Co., Ltd.); anhydrous Na2CO3 (superior grade pure, Tianjin Kemiou Chemical Reagent Co., Ltd.); NaHCO3 (superior grade pure, Tianjin Guangfu Technology Development Co., Ltd.); standard substance of iodine ion solution in water (100 mg / L, National Institute of Metrology, China).

[0019] 1.2 Preparation of standard solutions

[0020] Take the standard substance of iodine ion solution in water and dilute it step by step with water to obtain standard series solutions with concentrations of 5.0, 10.0, 50.0, 200.0, 500.0, 1000.0, 5000.0 μg / L respectively.

[0021] 1.3 Sample pretreatment method

[0022] Take the sample solution through a 0.45 μm microporous filter membrane and directly load it onto the machine.

[0023] 1.4 Liquid chromatography conditions

[0024] Chromatographic column: Metrosep A Supp5-250 chromatographic column (250 mm × 4.0 mm, 5 μm); column temperature: 50 °C; injection volume: 100 μl; flow rate: 0.60 mL / min; mobile phase: 4.5 mmol / L Na2CO3 + 1.0 mmol / L NaHCO3 + 35% acetonitrile. Detection wavelength: 226 nm.

[0025] 2 Experimental results

[0026] 2.1 Selection of detection wavelength

[0027] The standard solution of iodine ion was scanned in the ultraviolet band to obtain the ultraviolet absorption diagram of iodine ion, as shown in Figure 1 . From Figure 1It can be known that the maximum absorption wavelength of iodide ion is 226 nm.

[0028] 2.2 Selection of chromatographic column

[0029] In this study, three chromatographic columns, namely Metrosep A Supp4-250, Metrosep A Supp5-250, and Metrosep A Supp7-250, were investigated, and the results are shown in Table 1. It can be seen from Table 1 that the Metrosep A Supp5-250 chromatographic column has the highest peak height, moderate retention time, and the narrowest peak width. Therefore, Metrosep A Supp5-250 was selected as the analytical chromatographic column.

[0030] Table 1 Selection of chromatographic column

[0031] Table 1 Selection of chromatographic column

[0032]

[0033] 2.3 Selection of organic modifier in the mobile phase

[0034] When the selected chromatographic column was Metrosep A Supp5-250, the mobile phase improvement study was carried out based on 4.5 mmol / L Na2CO3 + 1.0 mmol / L NaHCO3 + 15% acetonitrile. In the present invention, 4.5 mmol / L Na2CO3 + 1.0 mmol / L NaHCO3 was used as the mobile phase, and the organic modifier and its dosage were investigated. Generally, in ion chromatography, suitable organic solvents mainly include methanol, acetonitrile, and acetone. Since methanol mainly improves the separation degree in a relatively long time, and this study mainly aims to solve the problem of too long retention time of iodide ion to shorten the analysis time, acetonitrile and acetone were selected.

[0035] When the flow rate was 1.0 mL / min, the dosages of two organic modifiers, acetonitrile and acetone, were investigated. When using acetone, only the eluent with 5% acetone showed a peak, and the response value was lower than that of acetonitrile. At the same time, the peak width was relatively wide, reaching 2 min, and no peaks appeared within 25 min for 10%, 15%, 20%, 25%, 30%, 35%, and 40% acetone; when using acetonitrile, the higher the proportion of acetonitrile is not necessarily better, but the peak height of 35% acetonitrile is the highest and the response value is the largest, and the results are shown in Table 2. Therefore, 35% acetonitrile was selected as the organic modifier.

[0036] Table 2 Investigation of the dosage of organic modifier

[0037] Table 2Investigation of the dosage of organic improvers

[0038]

[0039]

[0040] 2.4 Selection of flow rate

[0041] The flow rate was investigated in the range of 0.50 - 1.20 mL / min. As the flow rate increased, the peak height gradually decreased and the pressure gradually increased. Among them, compared with 0.50 mL / min, the peak height difference was not significant at 0.60 mL / min, and the peak emergence time was 3.292 min less. The results are shown in Table 3. Therefore, the flow rate was selected as 0.60 mL / min.

[0042] Table 3Selection of flow rate

[0043] Table 3Selection of flow rate

[0044]

[0045] 2.5 Selection of column temperature

[0046] Since the operating temperature of the Metrosep A Supp5 - 250 chromatographic column is in the range of 20 - 60 °C, considering that the column temperature of 20 °C is not conducive to control, therefore, in this study, the column temperature in the range of 25 - 60 °C was investigated, and the results are shown in Table 4. The peak height was the highest and the peak area was the largest at 60 °C, but the peak was slightly front - extended. Considering that 60 °C is the maximum operating temperature of this chromatographic column, in order to extend its service life, finally 50 °C, which has a peak height not much different, was selected.

[0047] Table 4Selection of column temperature

[0048] Table 4Selection of column temperature

[0049]

[0050]

[0051] Example 2: Specificity experiment of the method of the present invention

[0052] The test was carried out according to the method described in item 1.4 of Example 1. The chromatogram of the standard solution of iodide is shown in Figure 2At this time, the chromatographic peak has good symmetry and a sharp peak shape. The theoretical plate number is 23762, and the tailing factor is 0.97. The chromatograms of four types of domestic drinking water, namely purified water, tap water, mineral water, and well water, are shown respectively in Figure 2 b in Figure 2 c in Figure 2 d in Figure 2 e in . It can be seen that there is no impurity interference before and after iodide in the chromatograms of purified water, tap water, mineral water, and well water, which can meet the analysis requirements.

[0053] Comparative Example 1: Comparison with the reported methods

[0054] At present, the main methods for the determination of iodide include spectrophotometry [11-13] , enzyme immunoassay

[14] , iodine electrode method

[15] , ion chromatography [16-23] , high performance liquid chromatography [24-27] , gas chromatography [28-29] , inductively coupled plasma mass spectrometry [6,30] . Among them, the spectrophotometry, enzyme immunoassay, and iodine electrode method are complex in operation, require the addition of various reagents, and need to be added manually, making it impossible to achieve online automation; although the ion chromatography is simple in operation and can also achieve online automation, the specificity of the conductivity detector and amperometric detector is inferior to that of the diode array detector of high performance liquid chromatography, and the latter can provide the spectrogram of the target substance; although high performance liquid chromatography has also been reported, among them, He Guangtao et al.

[24] and Liu Yujie et al.

[27] require the injector temperature to be 10°C, which is relatively strict and inconvenient to control, and the peak emergence time is earlier and the retention is weaker. Zhang Xiaotong et al.

[25] adopt reverse ion pair chromatography, and ion pair reagents need to be added to the mobile phase, and the samples need to be derivatized, with complex operations; the detection limit of iodide reported by Li Meng et al.

[26] is only 100 μg / L, which is much higher than the detection limit (2 μg / L) of this method; gas chromatography requires derivatization and has cumbersome operations; inductively coupled plasma mass spectrometry requires expensive instruments and is not conducive to popularization and application at the grass-roots level. In the national standard

[34] , when using the cerium sulfate catalytic spectrophotometry, if 0.3 mL of water sample is taken for determination, the lowest detectable mass concentration is 5.3 μg / L; when using the high-concentration iodide colorimetry, if 10 mL of water sample is taken for determination, the lowest detectable mass concentration is 0.05 mg / L; when using the high-concentration iodide volumetric method, if 100 mL of water sample is taken for determination, the lowest detectable mass concentration is 0.025 mg / L; when using inductively coupled plasma mass spectrometry, the lowest detectable mass concentration is 0.6 μg / L. The detection limit of this method is 2.0 μg / L, which is better than the spectrophotometry and volumetric method in the national standard. Moreover, the sample can be directly filtered through the membrane and injected into the instrument without complex pretreatment process, and no toxic and harmful chemical reagents are used. It can also achieve online automatic sampling, which has obvious advantages for a large number of samples; compared with inductively coupled plasma mass spectrometry, the instrument used is relatively cheap, which is conducive to popularization and application at the grass-roots level.

[0055] Excerpts of attached references:

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[34] GB / T 5750.5-2023. Standard Examination Methods for Drinking Water - Part 5: Inorganic Nonmetallic Indices. National Standards of the People’s Republic of China (Drinking Water Standard Test Methods - Part 5: Inorganic Nonmetallic Indicators. National Standards of the People’s Republic of China).

[0078] Example 3: Methodology Evaluation

[0079] The methodology evaluation was carried out according to the detection method of the present invention described in Example 1.

[0080] 1 Linear Range, Detection Limit and Quantitation Limit

[0081] The prepared standard solution series was injected into the liquid chromatograph and analyzed according to the chromatographic conditions described in item 1.4 of Example 1. With the mass concentration X (μg / L) of the standard as the abscissa and the peak area Y as the ordinate, a linear regression was performed. The concentration at a signal-to-noise ratio (S / N) of 3 was used as the method detection limit (LOD), and the concentration at a signal-to-noise ratio (S / N) of 10 was used as the method quantitation limit (LOQ). The results showed that iodide had a good linear relationship in the range of 5.00 - 5000 μg / L, the linear equation was Y = 0.9837X - 5.7126, and r = 0.9999. The LOD of the method of the present invention was 2 μg / L, and the LOQ was 5 μg / L.

[0082] 2 Stability of Reference Substances

[0083] Take the standard solutions of iodide ions in water with mass concentrations of 100 and 500 μg / L, and perform 6 parallel determinations. The RSD values of the retention time were 0.01% - 0.02%, and the RSD values of the content were 0.42% - 0.44%. Take the above solutions and place them at room temperature, and inject and measure them at 0, 2, 4, 6, 8, 12, 24, and 48 h after preparation to obtain the stability results of the reference substances. The RSD values of the content of the standard solution of iodide ions in water within 48 hours were 0.53% - 0.59%. It shows that the repeatability of the instrument is good, and the reference substance solution has good stability within 48 hours.

[0084] 3 Accuracy and Precision

[0085] Using purified water, tap water, mineral water and well water as matrices respectively, a spike recovery experiment was carried out in a three-level and six-parallel manner (see Table 5). The results showed that at three different spiked levels, the average recoveries of iodide in the above samples were 97.2% - 109.9%, and the relative standard deviations (RSD, n = 6) were all lower than 0.97%. The recovery rate of this method is good and the accuracy is high, and it can determine the content of iodide in drinking water.

[0086] Table 5 Contents, spiked recoveries and relative standard deviations of iodide in real samples (n = 6)

[0087] Table 5 Contents and spiked recoveries and relative standard deviations of iodide in real samples (n = 6)

[0088]

[0089]

[0090] / : no data.

[0091] Example 4: Detection of real samples

[0092] The method described in Example 1 was used to determine iodide in four kinds of drinking water, namely purified water, tap water, mineral water and well water. Except for the well water containing 32.92 μg / L iodide, the other three kinds of drinking water did not contain iodide. The content of iodide in the well water meets the requirement of iodide being lower than 0.1 mg / L in the Hygienic Standard for Drinking Water (GB 5749 - 2022).

[0093] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the detailed contents in detail, nor limit the invention to the specific embodiments described. Obviously, according to the content of this specification, other related modifications can be made. This specification selects and specifically describes these embodiments to better explain the principle and practical application of the present invention, so that those skilled in the art in the relevant technical field can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A method for determining iodide in drinking water, characterized in that: The iodide in drinking water is determined by high performance liquid chromatography - ultraviolet detection method; the drinking water sample solution is taken for detection, and the external standard method is used for quantification; the detection method is as follows: separation is carried out using a Metrosep A Supp5 - 250 chromatographic column (250 mm×4.0 mm, 5 μm), with 4.5 mmol / L Na2CO3 + 1.0 mmol / L NaHCO3 + 5% acetone or 0% - 35% acetonitrile as the mobile phase, the flow rate is 0.50 - 1.20 mL / min, and the column temperature is 25 - 60 °C.

2. The method according to claim 1, wherein: The drinking water sample solution is passed through a 0.45 μm microporous filter membrane and directly detected on the machine.

3. The method according to claim 1, wherein: The ultraviolet detection uses a DAD detector.

4. The method according to claim 3, wherein: The ultraviolet detection wavelength is 226 nm.

5. The method according to claim 1, characterized in that: The flow rate is 0.60 mL / min.

6. The method according to claim 1, characterized in that: The column temperature is 50 °C.

7. The method according to claim 1, wherein: The mobile phase is 4.5 mmol / L Na2CO3 + 1.0 mmol / L NaHCO3 + 0% - 35% acetonitrile.

8. The method according to claim 7, wherein: The mobile phase is 4.5 mmol / L Na2CO3 + 1.0 mmol / L NaHCO3 + 35% acetonitrile.

9. The detection method according to claim 1, characterized in that: The drinking water sample is purified water or tap water or mineral water or well water.

10. Application of the method according to any one of claims 1 - 9 in the determination of iodide in drinking water.

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