A method for detecting ferrous ions (Fe2+) in the environment

Abstract

This invention discloses a method for detecting ferrous ions (Fe2+) in the environment, belonging to the field of heavy metal ion detection. The method includes the following steps: (1) adding a chromogenic agent tetrakis(4-carboxyphenyl)porphyrin and a surfactant to the sample to be tested, adjusting the pH of the system to acidic, mixing thoroughly, and allowing the mixture to stand for reaction; (2) after the reaction is complete, measuring the absorbance of the solution using spectrophotometry, and calculating the concentration of ferrous ions in the sample based on the standard curve of ferrous ions. In this method, ferrous ions react with the chromogenic agent to form a stable orange-red complex, exhibiting high sensitivity, strong anti-interference ability, and stable chromogenic agent. This overcomes the shortcomings of the current o-phenanthroline spectrophotometric method for determining ferrous ions, which suffers from low sensitivity, poor anti-interference ability, and poor chromogenic agent stability. This method does not rely on large instruments and equipment, is easy to operate, and is very suitable for the rapid detection of trace ferrous ions in water.

Description

Technical Field

[0001] This invention belongs to the field of heavy metal ion detection, and particularly relates to a method for detecting ferrous ions in the environment. Background Technology

[0002] Iron ions play a central role in natural cycles and human activities, and are widely distributed in natural water bodies and soil environments. In the environmental field, Fe2+ is abundant in groundwater and surface water. 2+ The content of Fe directly indicates the redox state and dissolved oxygen level of a water body. Its dynamic changes not only affect the sensory characteristics of water quality and drive the migration of pollutants, but may also cause ecological hypoxia. Therefore, it is a key parameter for assessing drinking water safety and ecosystem balance. 2+ The environmental behavior of phosphorus is complex. Its redox processes directly regulate the speciation and migration of heavy metals, the degradation of organic pollutants, and the bioavailability of phosphorus in water, thus profoundly impacting overall ecosystem health, water quality safety, and soil function. Therefore, the environmental impact of Fe... 2+ Accurate and timely concentration monitoring and speciation identification are crucial for assessing environmental pollution, tracing pollution sources, studying elemental geochemical behavior, and implementing effective environmental management and remediation strategies. The current industry standard HJ / T 345-2007 uses the o-phenanthroline spectrophotometric method to determine Fe. 2+ The minimum detection concentration is 0.03 mg / L, resulting in low sensitivity that cannot meet the requirements of high-sensitivity detection items. The chromogenic reagent, o-phenanthroline, is easily decomposed by light, exhibiting poor stability and a short shelf life. Furthermore, o-phenanthroline can form colored complexes with various metal ions, exhibiting poor anti-interference ability. Therefore, there is an urgent need to develop a Fe chromogenic reagent with high sensitivity, good stability, and strong anti-interference ability. 2+ A rapid detection method. Summary of the Invention

[0003] Objective of the Invention: To address the aforementioned technical problems, this invention aims to provide a method for detecting ferrous ions (Fe2+) in the environment. This method employs specific detection techniques and conditions, and utilizes tetrakis(4-carboxyphenyl)porphyrin as a chromogenic reagent containing substances that react with Fe2+. 2+ With highly compatible coordination sites, the method of this invention exhibits high sensitivity, high stability, and simple operation, and can effectively detect Fe in water such as industrial wastewater simultaneously. 2+ The method for detecting ferrous ions in water is simple, highly sensitive, and fully meets the existing maximum limit requirements. It is a new method for detecting ferrous ions in water that is easy to promote and use, and has strong innovative significance and practical value.

[0004] Technical solution: To achieve the above objectives, the present invention provides a method for detecting ferrous ions (Fe2+) in the environment, comprising the following steps:

[0005] (1) Add the colorimetric reagent tetra(4-carboxyphenyl)porphyrin and surfactant to the sample to be tested, adjust the pH of the system to acidic, mix well and let it stand to react;

[0006] (2) After the reaction is complete, the absorbance of the solution is measured by spectrophotometry, and the concentration of ferrous ions in the sample is calculated according to the standard curve of ferrous ions.

[0007] The chromogenic agent tetra(4-carboxyphenyl)porphyrin has the following structural formula: .

[0008] In step (1), the preparation of the indicator tetra(4-carboxyphenyl)porphyrin involves adding pyrrole and 4-carboxybenzaldehyde to acetic acid and refluxing them. After cooling the mixture, anhydrous ethanol is added, and the temperature is lowered to room temperature with stirring. The mixture is then continuously stirred, allowed to stand at low temperature, and the product is collected by vacuum filtration. After washing and drying, tetra(4-carboxyphenyl)porphyrin is obtained.

[0009] The method for preparing the colorimetric reagent tetra(4-carboxyphenyl)porphyrin involves adding pyrrole and 4-carboxybenzaldehyde to acetic acid and heating under reflux at 135°C for 1 hour. The mixture is then cooled to 80°C, anhydrous ethanol is added, and the temperature is lowered to room temperature with stirring for 3 hours. The mixture is then stored in a refrigerator for 24 hours. The product is collected by vacuum filtration and washed with cold acetone. After vacuum drying, the colorimetric reagent is obtained.

[0010] Preferably, the method for preparing the colorimetric reagent involves adding 4.0 mL of pyrrole and 8.59 g of 4-carboxybenzaldehyde to 120 mL of acetic acid and heating under reflux at 135 °C for 1 hour. The mixture is then cooled to 80 °C, 50 mL of anhydrous ethanol is added, and the temperature is lowered to room temperature with stirring for 3 hours. The mixture is then stored in a refrigerator for 24 hours. The product is collected by vacuum filtration and washed with cold acetone. After vacuum drying, tetrakis(4-carboxyphenyl)porphyrin is obtained with a purity of 95% and a yield of 57%.

[0011] In step (1), the surfactant is any one or a combination of hydroxylamine hydrochloride, Tween-80, and sodium dodecyl sulfate (SDS). The amount of surfactant added is 0.4 to 2.0 mL, and the concentration is 1 to 5%.

[0012] Preferably, the surfactant in step (1) is hydroxylamine hydrochloride.

[0013] Furthermore, the surfactant is a 4% hydroxylamine hydrochloride solution, used in a volume of 1 mL.

[0014] In step (1), the amount of the colorimetric reagent tetra(4-carboxyphenyl)porphyrin added is 0.2~5.0 mL, and the concentration is 0.1~2.5 g / L.

[0015] Preferably, in step (1), the amount of chromogenic agent tetra(4-carboxyphenyl)porphyrin added is 2.0 mL, and the concentration of the chromogenic agent is 1 g / L.

[0016] In step (1), hydrochloric acid or sulfuric acid is used to adjust the pH of the system to an acidic level of 3 to 6.

[0017] Preferably, in step (1), a 20% hydrochloric acid solution is used to adjust the pH of the system to 3.

[0018] In step (1), the reaction time after mixing is 5~30 min and the temperature is 10~60℃.

[0019] Preferably, in step (1), the reaction time after mixing is 5~30 min and the temperature is 25~35℃.

[0020] More preferably, the mixing and standing time is 15 minutes and the temperature is 30°C.

[0021] Furthermore, in step (1), the interference of other metal ions is reduced by adding a masking agent, which includes thiourea, sodium citrate, and NaF.

[0022] Preferably, the masking agent comprises 1 mL of 0.1 mol / L thiourea, 1 mL of 0.1 mol / L sodium citrate, and 0.5 mL of 0.02 mol / L NaF.

[0023] In step (2), the absorbance of the solution is measured by spectrophotometry, and the maximum absorption wavelength of ferrous ions is 441 nm.

[0024] The environment mentioned here includes aquatic environment or soil environment.

[0025] The detection method and colorimetric reagent determination and analysis of the present invention mainly include the following steps:

[0026] Measurement condition optimization: By finely controlling the pH value, selecting the appropriate type and concentration of acid solution, optimizing the type and amount of microemulsion, determining the optimal maximum absorption wavelength, and setting the measurement parameters reasonably, the sensitivity, stability, and specific selectivity can be maximized.

[0027] Repeatability study: The same sample is tested multiple times to examine the repeatability of the test results under the same conditions, in order to evaluate the stability of the test method and reagents.

[0028] Method reliability assessment: The detection results of this invention are compared with standard solutions to verify its accuracy and precision, and to ensure the reliability of the detection method.

[0029] A standard curve was plotted using spectrophotometry, with the ferrous iron concentration of each ferrous iron standard solution and the absorbance value of the corresponding standard solution to be tested as the ordinate and the ferrous iron ion concentration as the abscissa.

[0030] Obtain the test solution, pretreat it, and then add acid to adjust the pH value of the test standard solution.

[0031] Add a colorimetric reagent and a homogenizing agent to the test solution, mix, and let stand.

[0032] The test solution containing Fe was analyzed by spectrophotometry. 2+ The detection wavelength was 441nm.

[0033] After the reaction is complete, the absorbance is measured by spectrophotometry. The measured absorbance value is then mapped to the standard curve to obtain the concentration of ferrous ions in the sample.

[0034] The linear equation of the standard curve for detecting divalent iron ions in this invention is y = 0.05237 + 1.02453x (R0). 2 =0.99773). According to this test method, the iron content of 10 blank reagents was determined. The test results showed that S=0.00164, L=3×SD blank / S, the detection limit was 0.0048 mg / L, and the accuracy was expressed as relative standard deviation, with RSD=2.46%.

[0035] This invention has excellent detection sensitivity and extremely low detection limit. Its detection process is green and environmentally friendly, does not rely on large instruments and equipment, and is simple, efficient and easy to operate.

[0036] This invention relates to a chromogenic reagent for detecting ferrous ions (Fe2+) with a molecular structure containing coordination sites that have a specific high affinity for ferrous ions, enabling the formation of stable complexes. Through specific structural optimization, this chromogenic reagent significantly enhances the recognition sensitivity for ferrous ions, resulting in a significant change in absorbance as the concentration of ferrous ions varies, thus achieving highly sensitive detection of low concentrations of ferrous ions. This chromogenic reagent not only possesses excellent selectivity and detection sensitivity but also exhibits ease of operation and good stability, making it suitable for the effective determination of ferrous ion content in water bodies and providing a reliable detection method for environmental monitoring.

[0037] Currently, the existing industry standard HJ / T 345-2007 uses the o-phenanthroline spectrophotometric method to determine ferrous ions, with a detection limit of 0.03 mg / L. This method has low sensitivity, making it difficult to detect trace amounts of ferrous ions, and the determination process also exhibits poor stability. The method of this invention is suitable for Fe... 2+ The detection limit can be as low as 0.0048 mg / L, and the sensitivity is 6 times higher than the current industry standard, meeting the needs of trace analysis. Secondly, the tetrakis(4-carboxyphenyl)porphyrin in the method of this invention... 2+ It exhibits stronger coordination recognition capabilities, better selectivity than o-phenanthroline, and simpler pretreatment procedures, improving Fe... 2+ The oxidative stability of ferrous ions is improved. Therefore, the specific detection method of this invention, through various designs and optimizations, overcomes the shortcomings of traditional industry standard spectrophotometric methods for detecting ferrous ions, providing a new approach for water quality monitoring and pollution control, and has very important practical significance.

[0038] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0039] 1. This invention provides a highly sensitive Fe 2+ The detection method utilizes a specific colorimetric reagent with Fe 2+ The ability to form stable complexes allows for significant absorbance changes even at low concentrations, thus enabling the monitoring of trace amounts of Fe. 2+ This method provides highly efficient detection of trace Fe in environmental water bodies and industrial wastewater. The detection limit is as low as 0.0048 mg / L, making it suitable for the detection of trace Fe. 2+ Simultaneous analysis has significant application value in the fields of environmental monitoring and health risk assessment.

[0040] 2. The detection method employed in this invention is based on a specialized colorimetric reagent and specific detection conditions. The operation process is extremely simple, requiring no expensive or complex large-scale instruments or equipment, significantly reducing the detection threshold and cost. This method features short detection time, high efficiency, and no strict requirements on the detection environment or operation time, exhibiting strong adaptability and enabling rapid determination under various field conditions. This not only greatly improves detection efficiency but also enhances the method's practicality and promotional value, making it particularly suitable for rapid on-site screening and real-time monitoring scenarios. It is of great significance for environmental protection and human health monitoring, providing a reliable and easy-to-implement technical means for instant detection in related fields. Attached Figure Description

[0041] Figure 1 The color change of the complex of the color developer and ferrous ions in this invention;

[0042] Figure 2 This is the ultraviolet absorption spectrum of the colorimetric reagent of this invention;

[0043] Figure 3 The image shows the ultraviolet absorption spectrum of the colorimetric reagent and the ferrous ion complex of this invention.

[0044] Figure 4 The effect of surfactants on the absorbance of ferrous ion complexes;

[0045] Figure 5 The graph shows the effect of different pH values ​​on the absorbance of ferrous ion complexes, where the colorimetric reagent complexes with metal ions under acidic conditions.

[0046] Figure 6 The graph shows the effect of hydroxylamine hydrochloride surfactant and its dosage on the absorbance of ferrous ion complexes.

[0047] Figure 7 The graph shows the effect of the amount of colorimetric reagent on the absorbance of the ferrous ion complex.

[0048] Figure 8 The graph shows the effect of time on the absorbance of the ferrous ion complex.

[0049] Figure 9 The graph shows the effect of temperature on the absorbance of ferrous ion complexes.

[0050] Figure 10 For the present invention Fe 2+ Absorbance standard curve fitting plot for concentrations (0-0.8 mg / L);

[0051] Figure 11 The chromogenic NMR spectrum is shown in the form of a hydrogen NMR spectrum.

[0052] Figure 12 This is the mass spectrum of the chromogenic reagent. Detailed Implementation

[0053] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0054] Unless otherwise specified, all materials and reagents used in the following examples are commercially available. Experimental methods not specifically described in the examples are generally performed under standard conditions or as recommended by the manufacturer.

[0055] The specific configurations of each reagent in the examples are as follows:

[0056] Preparation method of colorimetric reagent solution: Weigh 0.01~0.1 g of tetra(4-carboxyphenyl)porphyrin colorimetric reagent, dissolve it in DMF, and prepare a 100 mL solution with a concentration of 0.1~1.0 g / L.

[0057] Preparation of 20% hydrochloric acid solution: Take 100 g of concentrated hydrochloric acid (mass fraction of 36.5%) and add 82.5 g of water to prepare a 20% hydrochloric acid solution.

[0058] Preparation of 20% sulfuric acid solution: First, add 70 mL of water to a beaker. Measure 12.3 mL of 98% concentrated sulfuric acid and slowly pour it along the wall of the beaker into the water, stirring constantly with a glass rod to ensure even mixing and prevent splashing. After the solution cools to room temperature, add water to bring the volume to 100 mL and make up the difference. This will prepare a 20% sulfuric acid solution.

[0059] Preparation of sodium dodecyl sulfate solution: Weigh 4g of solid and dissolve it in 40ml of water, then dilute to 100ml with water to obtain a 4% sodium dodecyl sulfate solution.

[0060] Preparation of Tween-80 solution: Measure 4 ml of Tween-80, pour it into a beaker, stir well with deionized water, transfer it to a volumetric flask and make up to 100 ml to obtain a 4% Tween-80 solution.

[0061] Preparation of hydroxylamine hydrochloride solution: Weigh 4g of solid hydroxylamine hydrochloride, add 40ml of water to a beaker to dissolve it, transfer it to a volumetric flask, and make up to 100ml to obtain a 4% hydroxylamine hydrochloride solution.

[0062] Preparation of ferrous ammonium sulfate standard solution: Weigh 7.022 g of ferrous ammonium sulfate crystals accurately using an analytical balance, add about 500 mL of boiled and cooled distilled water, add 5 mL of dilute sulfuric acid (1 mol / L) to acidify, and dilute to 1 L in a volumetric flask. The resulting solution concentration is 1 mg / mL. Dilute to 1~5 mg / L before use.

[0063] Preparation of 0.1 mol / L thiourea solution: Accurately weigh 0.761 g of thiourea, dissolve it in a small amount of water, transfer it to a 100 mL volumetric flask, add water to the mark, and shake well to obtain a 0.1 mol / L thiourea solution.

[0064] Preparation of 0.1 mol / L sodium citrate solution: Accurately weigh 2.94 g of sodium citrate dihydrate, dissolve it in a small amount of water, transfer it to a 100 mL volumetric flask, add water to the mark, and shake well to obtain a 0.1 mol / L sodium citrate solution.

[0065] Preparation of 0.02 mol / L NaF solution: Accurately weigh 0.084 g of sodium fluoride, dissolve it in a small amount of water, transfer it to a 100 mL volumetric flask, add water to the mark, and shake well to obtain a 0.02 mol / L sodium fluoride solution.

[0066] Ferrous ammonium sulfate hexahydrate: analytical grade, Shanghai Bid Pharmaceutical Technology Co., Ltd., BD01406944;

[0067] Tween-80: Chemically pure, Shanghai Bid Pharmaceutical Technology Co., Ltd., BD148605;

[0068] Sodium dodecyl sulfate (SDS): analytical grade, Shanghai Bid Pharmaceutical Technology Co., Ltd., BD151446;

[0069] Hydroxylamine hydrochloride: analytical grade, Shanghai Bid Pharmaceutical Technology Co., Ltd., BD105730;

[0070] Hydrochloric acid: analytical grade, Sinopharm Chemical Reagent Co., Ltd., 20250427;

[0071] Sulfuric acid: analytical grade, Sinopharm Chemical Reagent Co., Ltd., 20250408.

[0072] Example 1

[0073] 4.0 mL of pyrrole and 8.59 g of 4-carboxybenzaldehyde were added to 120 mL of acetic acid and refluxed at 135 °C for 1 hour. The mixture was then cooled to 80 °C, and 50 mL of anhydrous ethanol was added. The temperature was lowered to room temperature with stirring for 3 hours. The mixture was then stored at 4 °C for 24 hours. The product was collected by vacuum filtration and washed with cold acetone. After vacuum drying, tetrakis(4-carboxyphenyl)porphyrin was obtained with a purity of 95% and a yield of 57%. The NMR characterization results of the obtained product were as follows: 1 HNMR (400 MHz, DMSO-d6) δ 13.31 (s, 4H), 8.84 (s, 8H), 8.38 (d, J = 8.3 Hz,8H), 8.34 – 8.29 (m, 8H), -2.94 (s, 2H). HR / MS (ESI) m / z: calculated forC 48 H 30 N4O8 [M + 1] + 791.21; found 791.25. The 1H NMR spectrum and mass spectrum of the chromogenic reagent prepared in this embodiment are shown below. Figure 11 and Figure 12 As shown.

[0074] The structure is as follows:

[0075]

[0076] Example 2

[0077] The application of the colorimetric reagent prepared in Example 1 in the detection of ferrous ions includes the following steps:

[0078] (1) The tetra(4-carboxyphenyl)porphyrin prepared in Example 1 is itself a pink liquid ( Figure 1 ),like Figure 2 As shown, an absorption peak is observed at 417 nm under UV-Vis spectrophotometry. When Fe is added... 2+ Occasionally, orange-red complexes TCPP-Fe are present. 2+ generate( Figure 1 That is, when 2 ml of 1 g / L colorimetric reagent solution is added to 5 ml of 2 mg / L ferrous standard solution, an orange-red complex TCPP-Fe is formed. 2+ (Generation), TCPP-Fe 2+ An absorption peak is generated at 441 nm, such as Figure 3 As shown.

[0079] (2) Determination of surfactants: Three different types of surfactants, namely 4% hydroxylamine hydrochloride, Tween-80, and sodium dodecyl sulfate (SDS), were prepared. 1 ml of each type of surfactant and 1 ml of deionized water were added to each, along with 5 ml of 2 mg / L ferrous standard solution and 2 ml of 1 g / L tetra(4-carboxyphenyl)porphyrin chromogenic reagent. 20% hydrochloric acid solution was added until the pH of the system reached 5, and the volume was adjusted to 10 ml with deionized water. After standing at room temperature for 15 min, the solution was measured using a UV spectrophotometer. The surfactant-free TCPP-Fe... 2+ The complex solution served as a control, such as... Figure 4 As shown, the TCPP-Fe of hydroxylamine hydrochloride surfactant 2+ The absorbance of the complex was similar to that of the control TCPP-Fe. 2+ The absorbance of the complex was significantly higher, so hydroxylamine hydrochloride was chosen as the surfactant.

[0080] (3) pH determination: Prepare systems with different pH values. Take 1 mL of 4% hydroxylamine hydrochloride solution, 5 mL of 2 mg / L ferrous standard solution, and 2 mL of 1 g / L colorimetric reagent solution. Add 20% hydrochloric acid solution until the pH of the system is 4-9, and then dilute to 10 mL with deionized water. After standing at room temperature for 15 min, measure the pH using a UV spectrophotometer. Figure 5 As shown, in the system at pH=5, TCPP-Fe 2+ The complex had the highest absorbance value, so a reaction system with pH=5 was ultimately chosen.

[0081] (4) Take 0.4 mL, 0.6 mL, 0.8 mL, 1.0 mL, 1.2 mL, 1.4 mL, 1.6 mL, 1.8 mL, and 2.0 mL of 4% hydroxylamine hydrochloride, respectively, and add 5 mL of 2 mg / L ferrous standard solution and 2 mL of 1 g / L tetra(4-carboxyphenyl)porphyrin colorimetric reagent to each solution. Add 20% hydrochloric acid solution until the pH of the system is 5, and then dilute to 10 mL with deionized water. After standing at room temperature for 15 min, determine the concentration using a UV spectrophotometer. (The last sentence appears to be incomplete and possibly refers to a specific method or method.) 2+ The complex solution served as a control, such as... Figure 6 As shown, the absorbance of 4% hydroxylamine hydrochloride surfactant at a dosage of 1.0 mL is the highest and most stable.

[0082] (5) Determination of the optimal amount of colorimetric reagent: Mix 1 mL of 4% hydroxylamine hydrochloride solution with 5 mL of ferrous standard solution with a concentration of 2 mg / L, and add 0.2 mL, 0.4 mL, 0.7 mL, 1.0 mL, 1.5 mL, and 2.0 mL of tetrakis(4-carboxyphenyl)porphyrin solution (1 g / L) respectively. Add 20% hydrochloric acid solution to the pH of the system to 5, and then dilute to 10 mL with deionized water. After standing at room temperature for 15 min, measure the absorbance of the complex using a UV spectrophotometer. As the amount of colorimetric reagent increases, the absorbance of the complex gradually increases; for example... Figure 7 When the amount of colorimetric reagent reaches 1.5~2.0 mL, the absorbance increases to its maximum and tends to stabilize. Therefore, 2.0 mL was selected as the optimal amount of colorimetric reagent for the determination.

[0083] (6) According to the optimal method in step (5), the static reaction time is 5-30 min. For example... Figure 8 As shown, when the reaction time reaches 15 min, the absorbance increases to its maximum and tends to stabilize.

[0084] (7) According to the optimal method in step (6), the temperature during the static reaction is 10-60 ℃. For example... Figure 9 As shown, the absorbance increases to its maximum when the reaction temperature is 30 °C.

[0085] Example 3

[0086] Prepare the colorimetric reagent solution (concentration of 1 g / L) prepared in Example 1, 20% hydrochloric acid solution, and 4% hydroxylamine hydrochloride solution. At the same time, prepare ferrous ion solutions of different concentrations for later use. Each substance is detected according to the optimal addition amount and optimal detection method in step (7) of Example 2.

[0087] The determination was performed spectrophotometrically. The chromogenic reagent reacted with different concentrations of ferrous ions to form complexes, with a solution of the same concentration of chromogenic reagent serving as a blank control. The absorbance of each concentration of the complex solution and the blank control solution was measured. A standard working curve was plotted with the difference in absorbance as the ordinate and the corresponding ferrous ion concentration as the abscissa. Figure 10 As shown, within the concentration range of 0–0.8 mg / L (ppm), the standard curve regression equation is y = 0.05237 + 1.02453x (R²). 2 =0.99773), the detection limit for ferrous ions was 0.0048 mg / L, and the detection range was 0–0.8 mg / L. Precision was evaluated by relative standard deviation (RSD), which was calculated to be 2.46%.

[0088] Example 4

[0089] 1. Anti-interference experiment

[0090] By adding a masking agent, interference from other metal ions can be reduced, thus achieving the effect of masking Fe. 2+ More accurate detection.

[0091] Experiments have shown that the tetra(4-carboxyphenyl)porphyrin in the method of this invention can produce color changes with Ag, Hg, Pb, Co, Cu, and Zn metal ions. To avoid the influence of other metal ions on Fe... 2+ To detect interference, a mixed masking agent was selected: 1 mL of 0.1 mol / L thiourea, 1 mL of 0.1 mol / L sodium citrate, 0.5 mL of 0.02 mol / L NaF, and 5 mL of 2 mg / L other metal ions and Fe were added according to the optimal method in step (7) of Example 2. 2+ The reaction was shown in Tables 1 and 2. The relative error of the permissible amount of various interfering ions was within ±5%. It was found that after adding the masking agent, other metal ions reacted with Fe. 2+ The coexistence ratio of Zn is: 2+ Pb 2+ Cu 2+ Co 2+ Hg 2+ Ni 2+ Mn 2+ (5); Ag + Cd 2+ (2.5); K + Na + Li + Ca 2+ Mg 2+ Ba 2+ Al 3+ (20) The detection of ferrous iron is not affected by the coexistence of other metal ions.

[0092] Table 1 Permissible amounts of coexisting ions

[0093]

[0094] Table 2 Permissible amounts of coexisting ions

[0095]

[0096] 2. Recovery rate experiment:

[0097] To verify the reliability of this method in actual samples, Fe in actual water samples was analyzed using the optimal method according to step (7) of Example 2. 2+ The detection work was carried out. Two samples were taken: Sample 1 was taken from the pickling solution of iron parts, and Sample 2 was taken from high-phosphorus wastewater from an electroplating company. 50 mL of the stock solution was filtered through a 2 μm filter membrane for analysis. The filtrate was colorless and transparent, without any interfering colors. The experimental environment was consistent with the previously optimized conditions, ensuring the accuracy of the colorimetric reaction. Samples containing 0, 0.3, and 0.6 mg / L Fe were selected. 2+ Spiked recovery experiments were conducted on two types of samples. The optimal method described in Example 2 of this invention, along with ICP-MS, was used to analyze the two groups of samples. As shown in Table 3, the recovery rate of the porphyrin colorimetric-spectrophotometric method ranged from 94.45% to 103.91%, indicating that the method is accurate and reliable, and the measured values ​​showed good consistency with the ICP-MS method. Compared with the industry standard o-phenanthroline spectrophotometric method, the method of this invention has a more stable recovery rate and stronger anti-interference ability at trace levels, making it more suitable for the rapid analysis and detection of trace ferrous ions in actual water samples. Even with complex sample compositions, this method can still detect Fe... 2+ Achieve highly selective recognition.

[0098] Table 3. Actual sample recovery rate

[0099]

[0100] In summary, the detection method of the present invention has higher sensitivity and meets the industry's maximum limit requirements. The method of the present invention is simple, fast, and easy to promote and use.

Claims

1. A method for detecting ferrous ions (Fe2+) in the environment, characterized in that, Includes the following steps: (1) Add the colorimetric reagent tetra(4-carboxyphenyl)porphyrin and surfactant to the sample to be tested, adjust the pH of the system to acidic, mix well and let it stand to react; (2) After the reaction is complete, the absorbance of the solution is measured by spectrophotometry, and the concentration of ferrous ions in the sample is calculated according to the standard curve of ferrous ions. The chromogenic agent tetra(4-carboxyphenyl)porphyrin has the following structural formula: ； The surfactant mentioned in step (1) is 4% hydroxylamine hydrochloride surfactant, with a dosage of 1.0 mL; the pH value of the system is adjusted to 5; the concentration of the colorimetric agent is 1 g / L, and the amount added is 2.0 mL; the reaction time after mixing in step (1) is 15 min, and the temperature is 30℃.

2. The method for detecting ferrous ions (Fe2+) in the environment according to claim 1, characterized in that, In step (1), the preparation of the agent tetra(4-carboxyphenyl)porphyrin involves adding pyrrole and 4-carboxybenzaldehyde to acetic acid and refluxing them. After cooling the mixture, anhydrous ethanol is added, and the temperature is lowered to room temperature with stirring. After stirring continuously and allowing it to stand at low temperature, the product is collected by vacuum filtration, washed, and dried to obtain tetra(4-carboxyphenyl)porphyrin.

3. The method for detecting ferrous ions (Fe2+) in the environment according to claim 1, characterized in that, In step (2), the absorbance of the solution is measured by spectrophotometry, and the maximum absorption wavelength of ferrous ions is 441 nm.

4. The method for detecting ferrous ions (Fe2+) in the environment according to claim 1, characterized in that, The environment includes aquatic or soil environments.

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