A rapid detection and quantification method for iodides based on ultraviolet-visible spectroscopy

Abstract

This invention discloses a rapid detection and quantification method for iodides based on ultraviolet-visible spectroscopy, belonging to the field of analytical detection technology. The method first filters the sample using a 0.45 μm filter membrane, adjusts the pH of the system to 5.0–7.0 with dilute nitric acid, adds sodium thiosulfate as a masking agent to eliminate interference from residual chlorine, and then adds ammonium persulfate as an oxidant. The iodide is then detected and quantified in a water bath at 70–85 °C. ‑ Oxidized to I3 ‑ After the reaction, the sample was cooled and brought to a constant volume. The absorbance was then measured at 352 nm using a UV-Vis spectrophotometer in the 200–500 nm wavelength range. The iodide content was calculated using the standard curve. This method features a well-matched combination of reagents and reaction parameters, strong anti-interference capabilities, and effectively solves the problems of poor selectivity and large result deviations in traditional detection methods. This approach is simple to operate, uses readily available reagents, and has high detection sensitivity. It combines precise laboratory quantification with rapid on-site screening capabilities, exhibits good system stability and reproducibility, and can be widely applied to the detection of iodides in water, food, and other samples.

Description

Technical Field

[0001] This invention relates to the fields of analytical chemistry and environmental testing technology, specifically to a rapid identification and quantitative analysis method for iodides in water samples, food samples, and other samples based on ultraviolet-visible spectroscopy. Background Technology

[0002] Iodides are a key indicator in environmental monitoring, food safety, and clinical diagnostics. Accurate detection of iodide content in various samples is crucial for controlling environmental quality, food safety, and conducting relevant clinical assessments. Therefore, developing efficient and practical iodide detection technologies has significant real-world application value. Currently, several mature iodide detection methods exist in the industry, among which ion chromatography and inductively coupled plasma mass spectrometry (ICP-MS) are widely used due to their accurate results and are the mainstream methods for quantitative iodide detection. However, these two technologies have significant drawbacks. Not only are the supporting detection equipment expensive, but they also require highly skilled personnel and suitable testing sites. Furthermore, the sample pretreatment process is cumbersome, and the overall detection cycle is long. The complexity of these processes makes them unsuitable for rapid on-site screening and large-scale, real-time testing of samples, severely limiting their application scenarios.

[0003] Ultraviolet-visible spectrophotometry is a commonly used technique in analytical testing. Its greatest advantages lie in its simple equipment structure, concise detection process, and fast detection speed, with relatively low hardware costs and low barriers to entry, theoretically making it well-suited for rapid on-site testing. However, directly applying this technique to iodide detection exposes several unavoidable problems. Firstly, the actual sample matrices are often complex and diverse; water, food, and soil samples often contain multiple ions such as chloride and bromide, which can significantly interfere with the detection process. Secondly, iodide ions themselves have weak absorption peak specificity in the ultraviolet region, resulting in a lack of prominent characteristic signals and an inability to effectively distinguish them from interfering substances. Under the combined effect of these multiple factors, the selectivity of traditional ultraviolet-visible spectrophotometry for direct iodide detection decreases significantly, making it difficult to guarantee the accuracy of the final detection data and hindering stable and reliable iodide identification and quantification.

[0004] A review of current detection technologies reveals a polarization in iodide detection methods: high-precision methods rely on sophisticated equipment, are cumbersome and time-consuming, making rapid on-site testing difficult; while ultraviolet-visible spectrophotometry, with its simple equipment and rapid detection, suffers from poor anti-interference capabilities and weak characteristic absorption, resulting in inadequate detection performance for applications. Therefore, there is an urgent need for an iodide detection technology that is highly resistant to interference, accurate, easy to operate, and applicable on-site to better meet the needs of rapid identification and quantitative analysis of iodides in environmental monitoring, food safety, and clinical diagnosis. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a rapid detection and quantification method for iodides based on ultraviolet-visible spectroscopy, comprising the following steps: S1. Take the sample to be tested, filter it using a filter membrane, and adjust the pH of the system to 5.0-7.0 by adding acid; S2. Add masking agent and perform masking treatment; S3. Add an oxidizing agent and heat I under heating conditions. - Oxidized to I3 - ; S4. Cool, bring to volume, place in a UV-Vis spectrophotometer to scan the 200-500nm spectrum, use ultrapure water as a reference, and record the absorbance at 352nm. S5. Quantitatively calculate the iodide content in the sample to be tested based on the iodide content standard curve.

[0006] First, the sample is filtered to remove suspended solids and impurities, preventing interference from scattering light and protecting the detector. Then, the pH of the system is adjusted from a weakly acidic to a neutral range of 5.0–7.0 to facilitate the oxidation of iodide ions to I3. - The reaction provides a suitable chemical environment to ensure complete reaction and stable absorption peaks. A masking agent is then added to eliminate the influence of interfering substances such as residual chlorine in the sample, improving detection selectivity. Next, an oxidant is added and combined with heat treatment, which converts iodine ions with weak UV absorption signals and poor specificity into I3+ ions with strong characteristic absorption. - This process amplifies the detection signal and improves sensitivity, while also accelerating the reaction rate to ensure complete conversion of iodide ions and avoid deviations in quantitative results. After the reaction, the solution is cooled before being brought to a constant volume to standardize the temperature and volume, avoiding systematic errors caused by temperature and volume changes and ensuring that the sample system is consistent with standard detection conditions. Subsequently, a spectral scan is performed in the wavelength range of 200–500 nm, and the absorbance is recorded. This band can accurately capture I3 at 352 nm. - The characteristic absorption peaks are observed while avoiding interference from coexisting ions such as chloride and bromide ions, thus enabling qualitative identification of iodides. Finally, using Lambert-Beer's law and a pre-established standard curve for iodide content, the actual concentration of iodides in the sample is calculated based on the measured absorbance, completing the entire qualitative identification and precise quantitative detection process.

[0007] As an feasible example, the filter membrane has a pore size of 0.1-0.5μm. Using a filter membrane with a pore size of 0.1-0.5μm can effectively trap fine suspended particles and colloidal impurities in the sample. This can completely eliminate the scattering and obstruction of light path by particles, ensuring accurate spectral detection results, while not trapping the iodine ions to be measured, thus avoiding the loss of the target substance. At the same time, it is suitable for the filtration needs of various samples such as water samples and food extracts.

[0008] As an feasible example, the acid includes one of acetic acid, nitric acid, and citric acid. In this invention, nitric acid is preferred for adjusting the pH value. Nitric acid is a strong acid, adjusts pH quickly, can precisely control the pH of the system within the target range, requires a small amount, does not significantly change the solution volume, and is suitable for existing reaction systems. Furthermore, nitrate ions are chemically stable at room temperature and under 70-85℃ water bath conditions, do not possess redox properties, and will not react with sodium thiosulfate, ammonium persulfate, or I-. - I3 - Side reactions occur, ensuring the smooth progress of oxidation and colorimetric reactions; simultaneously, nitric acid and its ions have no characteristic absorption in the 200-500 nm detection band, thus avoiding baseline elevation and interference with I3 at 352 nm. - Detection of characteristic peaks; nitrate ions are not halide ions and do not affect I3. - A balance exists, which can avoid interference from chloride ions, sulfate ions, and other ions. In addition, dilute nitric acid is common, readily available, easy to prepare, and has controllable corrosivity, making it suitable for laboratory testing and rapid on-site screening. It can effectively ensure the stability of the method and the reproducibility of the experiment, and has the best overall compatibility compared to acids such as acetic acid, hydrochloric acid, and sulfuric acid.

[0009] As an implementable example, the masking agent includes one or more of sodium thiosulfate, glycine, aminosulfonic acid, triethanolamine, EDTA-2Na, sodium citrate, and sodium tartrate; sodium thiosulfate is preferred in this invention.

[0010] Furthermore, the amount of masking agent added is 0.1-1 mL, and the molar concentration of the masking agent is 0.1-0.5 mol / L.

[0011] Residual chlorine in the sample is a strong oxidizing agent and easily reacts with iodide ions, affecting the detection results. Sodium thiosulfate, as a moderately strong reducing agent, preferentially reacts with residual chlorine in a redox reaction, completely consuming the chlorine and generating a stable product, thus eliminating interference at the source. After the residual chlorine is completely removed, there are no additional oxidizing impurities in the system, and the subsequently added oxidant can quantitatively oxidize iodide ions to I3. -This ensures the smooth progress of the colorimetric reaction and ultimately guarantees the accuracy and reliability of iodide detection results. Simultaneously, sodium thiosulfate reagent, acting as a masking agent, is stable in a weakly acidic to neutral environment (pH 5.0–7.0), maintaining the system's pH and effectively eliminating interference from premature oxidation of iodide ions by residual chlorine, thus ensuring the normal progress of subsequent oxidation reactions. Furthermore, sodium thiosulfate and its reaction products exhibit no characteristic absorption in the 200–500 nm wavelength range, thus not interfering with I3 at 352 nm. - The detection signal is inexpensive, readily available, safe, non-toxic, easy to operate, and has a fast reaction rate. When used properly, it will not consume subsequent oxidants.

[0012] This invention limits the masking agent molar concentration to 0.1~0.5mol / L and the addition volume to 0.1~1mL. This ensures sufficient reagent quantity to completely neutralize residual chlorine and other oxidizing interferences in the sample, maximizing the masking effect. It also strictly controls the overall dosage to prevent excessive sodium thiosulfate. Excessive dosage will consume the subsequent ammonium persulfate oxidant, resulting in incomplete oxidation of iodide ions and lower detection results. Furthermore, this appropriate concentration and small volume range are suitable for the reaction system and volume adjustment specifications of this method, maintaining the original pH environment and reaction conditions without introducing additional turbidity or spectral interference. It balances masking effectiveness and detection accuracy, standardizes experimental conditions, and improves method repeatability.

[0013] As an implementable example, the oxidant includes one or more of hydrogen peroxide, ammonium persulfate, potassium permanganate, or sodium nitrite; the preferred oxidant in this invention is ammonium persulfate.

[0014] Furthermore, the amount of oxidant added is 0.1-1 mL, and the molar concentration of the oxidant is 0.1-1 mol / L.

[0015] Ammonium persulfate is a preferred oxidant because it is stable in this acidic or alkaline environment and can exert its oxidation effect steadily when the temperature is set, thus enabling it to convert I... - Quantitative and directional oxidation to generate I3 - This effectively avoids the formation of iodate ions due to insufficient or excessive oxidation, ensuring the stability of the target product. Furthermore, both the product itself and its reduction products exhibit no characteristic absorption in the 200–500 nm wavelength range, thus avoiding interference with I3 at 352 nm. -The characteristic absorption peak detection of ammonium persulfate is superior to that of reagents such as potassium permanganate. Furthermore, under standardized dosage, it exhibits good compatibility with sodium thiosulfate, minimizing masking agent consumption and ensuring the orderly execution of the two-step reaction of masking residual chlorine and iodine ion oxidation. In addition, ammonium persulfate is readily available, low-cost, stable in storage, and easy to operate. Its mild reaction conditions make it suitable for both laboratory batch testing and rapid on-site screening. Within a usage range of 0.1–1 mol / L concentration and 0.1–1 mL addition, it demonstrates strong reaction consistency, minimal influence from the sample matrix, stable detection data, and good reproducibility. Its overall performance surpasses that of alternative oxidants such as hydrogen peroxide, potassium permanganate, and sodium nitrite, avoiding the problems of excessive oxidation, spectral interference, poor stability, or toxicity associated with other reagents.

[0016] As an feasible example, in step S3, the heating temperature is 70-85℃, and the heating time is 5-10 minutes. Limiting the heating temperature to 70-85℃ and controlling the duration to 5-10 minutes ensures that iodide ions in the system are rapidly and completely oxidized to I3. - This avoids incomplete reactions that could lead to low results, and also prevents excessive oxidation caused by excessively high temperatures or prolonged times, which could generate iodate and destroy the target analyte. Furthermore, the reaction conditions within this parameter range are mild, and the system exhibits good stability, ensuring the repeatability and accuracy of detection results across different samples, thus enabling rapid qualitative and quantitative detection.

[0017] As an implementable example, the iodide content standard curve is y = 0.0125x + 0.005, R0 2 =0.9995.

[0018] Furthermore, the iodide content standard curve is obtained by testing the potassium iodide standard solution using ultraviolet-visible spectrophotometry.

[0019] Beneficial effects (I) This invention effectively eliminates interference from oxidizing impurities such as residual chlorine in the sample by adding sodium thiosulfate as a masking agent. Simultaneously, a 0.1~0.5μm filter membrane is used to remove suspended particulate matter, avoiding light scattering caused by impurities. The method oxidizes iodide ions to I3. - Subsequently, detection is carried out using its unique characteristic absorption peak at 352nm. Common coexisting ions such as chloride and bromide ions have no absorption in this band. Combined with pH adjustment and reagent system optimization, the influence of matrix and coexisting ions is avoided from multiple dimensions, which greatly improves the detection selectivity. It is suitable for a variety of samples with complex composition, such as water samples and food extracts.

[0020] (ii) Since the original iodide ion has a weak ultraviolet absorption signal, this invention uses ammonium persulfate as the preferred oxidant. Under controllable conditions of a water bath at 70-85°C for 5-10 minutes, iodide ions are quantitatively converted into I3 with a higher molar absorptivity. -This effectively amplifies the detection signal and improves detection sensitivity. The entire set of experimental parameters is strictly limited, including the concentration and volume of the oxidant and masking agent, the acid / alkaline environment, reaction temperature, and reaction time, ensuring a complete reaction without excessive oxidation. Combined with a standard curve for concentration calculation, the detection results are stable, with minimal deviation, and the quantitative results are accurate and reliable.

[0021] (III) This method features a simple sample pretreatment process. The entire process can be completed within ten minutes, consisting of filtration, pH adjustment, reagent addition, water bath reaction, and spectral scanning. The reagents are easy to prepare and use, the reaction conditions are mild, and no large-scale precision equipment or complex operational skills are required. Operators can learn to use the method with minimal training. Unlike time-consuming and cumbersome detection methods such as ion chromatography and mass spectrometry, this method enables rapid batch detection of samples, meeting not only the needs of routine laboratory analysis but also being highly suitable for rapid on-site screening.

[0022] (iv) The core instrument of this invention is a conventional ultraviolet-visible spectrophotometer, whose purchase and operating costs are far lower than those of high-end equipment such as ion chromatographs and inductively coupled plasma mass spectrometers. The reagents used in the experiment, such as ammonium persulfate, sodium thiosulfate, and dilute nitric acid, are all commonly used laboratory consumables, inexpensive, easy to procure, and require no special storage or transportation requirements. The entire detection scheme is economical and feasible, lowering the threshold for iodide detection. It can be widely applied to various matrix samples such as drinking water, surface water, and food, covering multiple fields including environmental monitoring and food safety.

[0023] (V) This method sets clear ranges for pH, reaction temperature, reaction time, and the concentration and amount of various reagents, forming a standardized operating system. Reagents such as dilute nitric acid and ammonium persulfate are chemically stable and will not cause side reactions or spectral interference under the given reaction conditions. Uniform experimental conditions effectively reduce systematic errors, and the detection data from different personnel and different batches of samples show good parallelism and strong reproducibility. The method has a high degree of standardization, making it easy to promote and use in routine testing. Detailed Implementation

[0024] Example 1 S1. Take 100 mL of tap water (containing I) as the test sample. - The solution was filtered using a 0.45 μm filtration membrane, and 10 mL of the filtrate was transferred to a 25 mL colorimetric tube. Dilute nitric acid was added to adjust the pH of the system to 6.0. S2. Add 1 mL of 0.1 mol / L sodium thiosulfate solution and perform masking treatment for 10 min; S3. Add 1 mL of 0.1 mol / L ammonium persulfate solution, heat in a 75°C water bath for 8 minutes, and then add I. - Oxidized to I3 - (The solution is pale yellow at this point); S4. Cool to room temperature (25℃), bring volume to 25mL, transfer to a 1cm quartz cuvette, place in a UV-Vis spectrophotometer to scan the 200-500nm spectrum, use ultrapure water as a reference, and record the absorbance at 352nm. The actual measured absorbance is 0.245. S5. According to the standard curve of iodide content, y = 0.0125x + 0.005 (R 2 =0.9995), the concentration of iodide in the sample was quantitatively calculated to be 19.2 μg / L.

[0025] Comparative Example 1 The specific implementation method of this example is the same as that of Example 1, except that step S3 is not included, that is, no oxidation treatment is performed, no obvious absorption peak is observed at 352nm, and no iodide is detected in the same test sample.

[0026] Results Analysis Example 1: All experimental steps were performed completely. After filtration, pH adjustment, masking, ammonium persulfate oxidation, and spectral detection, the absorbance was measured at 352 nm as 0.245. Based on the standard curve, the concentration of iodide in the tap water sample was calculated to be 19.2 μg / L, thus successfully achieving qualitative identification and accurate quantification of iodide.

[0027] Comparative Example 1 removed the oxidation step, and the remaining operations were completely consistent with Example 1. Finally, no obvious characteristic absorption peak was observed at 352 nm, and iodide could not be detected.

[0028] The two sets of experiments provide a stark contrast, directly demonstrating that the oxidation step is the core and key step in this detection method: the iodine ions (I-) in the raw water sample... - It has no specific absorption in the 200-500 nm wavelength range and cannot be identified by UV-Vis spectroscopy; it can only be identified by oxidation with ammonium persulfate. - Convert to I3 - Only then can a characteristic absorption signal be generated at 352nm. This also verifies that the entire pretreatment, reaction, and detection parameter set of this invention is reasonably matched, and that the oxidation, masking, and pH control processes work synergistically and effectively, resulting in a stable and reliable detection system that can accurately perform qualitative and quantitative analysis of iodides in water samples.

Claims

1. A rapid detection and quantification method for iodides based on ultraviolet-visible spectroscopy, characterized in that, Includes the following steps: S1. Take the sample to be tested, filter it using a filter membrane, and adjust the pH of the system to 5.0-7.0 by adding acid; S2. Add masking agent and perform masking treatment; S3. Add an oxidizing agent and heat I under heating conditions. - Oxidized to I3 - ; S4. Cool, bring to volume, place in a UV-Vis spectrophotometer to scan the 200-500nm spectrum, use ultrapure water as a reference, and record the absorbance at 352nm. S5. Quantitatively calculate the iodide content in the sample to be tested based on the iodide content standard curve.

2. The rapid detection and quantification method for iodides based on ultraviolet-visible spectroscopy according to claim 1, characterized in that, The filter membrane has a pore size of 0.1-0.5 μm.

3. The rapid detection and quantification method for iodides based on ultraviolet-visible spectroscopy according to claim 1, characterized in that, The acid mentioned includes one of acetic acid, nitric acid, and citric acid.

4. The rapid detection and quantification method for iodides based on ultraviolet-visible spectroscopy according to claim 1, characterized in that, The masking agent includes one or more of sodium thiosulfate, glycine, sulfamic acid, triethanolamine, EDTA-2Na, sodium citrate, and sodium tartrate.

5. The rapid detection and quantification method for iodides based on ultraviolet-visible spectroscopy according to claim 4, characterized in that, The amount of masking agent added is 0.1-1 mL, and the molar concentration of the masking agent is 0.1-0.5 mol / L.

6. The rapid detection and quantification method for iodides based on ultraviolet-visible spectroscopy according to claim 1, characterized in that, The oxidizing agent includes one or more of hydrogen peroxide, ammonium persulfate, potassium permanganate, or sodium nitrite.

7. The rapid detection and quantification method for iodides based on ultraviolet-visible spectroscopy according to claim 6, characterized in that, The amount of oxidant added is 0.1-1 mL, and the molar concentration of the oxidant is 0.1-1 mol / L.

8. The rapid detection and quantification method for iodides based on ultraviolet-visible spectroscopy according to claim 1, characterized in that, In step S3, the heating temperature is 70-85℃.

9. The rapid detection and quantification method for iodides based on ultraviolet-visible spectroscopy according to claim 1, characterized in that, In step S3, the heating time is 5-10 minutes.

10. The rapid detection and quantification method for iodides based on ultraviolet-visible spectroscopy according to claim 1, characterized in that, The standard curve for iodide content is: y = 0.0125x + 0.005, R0 2 =0.9995.