Preformed liquid for determining total iron in water, preparation method and determination method

Abstract

The invention discloses a prefabricated liquid for determining total iron in water, a preparation method and a determination method, and belongs to the technical field of water quality detection, every 1000 mL of the prefabricated liquid comprises 45-55 mL of concentrated hydrochloric acid, 20-30 mL of sodium hydroxide, 20-30 mL of sodium hydroxide, and the balance of water. 9 g to 11 g of hydroxylamine hydrochloride; 0.12 g to 0.18 g of phenanthroline hydrate; the acetic acid-sodium acetate buffer salt is used for adjusting the pH value of a final system to 4.5 + / -0.2; and the balance of deionized water. The invention provides a chemically stable and single-solution pre-prepared reagent, a strong acid extracting agent, a high-efficiency reducing agent and an iron ion color developing agent are premixed into a whole, the pre-mixed reagent maintains an extremely low pH value to maintain stability during storage through a specific buffer-stable system design, and after a water sample is added for dilution, the pH value of the system automatically rises to a range required by color development, so that the color development is realized. Therefore, the three-step reaction of acidolysis, reduction and color development can be automatically and continuously carried out. The corresponding determination method is very simple and convenient.

Description

Technical Field

[0001] This invention belongs to the field of water quality testing technology, specifically relating to a pre-prepared solution, preparation method, and testing method for determining total iron in water. Background Technology

[0002] Total iron concentration in water is a crucial indicator for evaluating water quality, assessing pipeline corrosion, and monitoring industrial pollution levels. Currently, the detection technology for iron in water faces several key technical bottlenecks and challenges in practical applications: The multi-component "coexistence-inhibition" challenge: Conventional colorimetric detection methods for iron ions require the sequential introduction of three core reagents—a reducing agent, a buffer, and a colorimetric agent. These three are difficult to coexist in a single stable solution system because the final reaction requires weakly acidic conditions. In this environment, the reducing agent is easily oxidized, and the colorimetric agent is prone to degradation, leading to a significant decrease in reagent stability.

[0003] Cumbersome operation and cumulative error: According to the standard testing procedure, the water sample must first be pretreated with an acidic reducing agent, then a buffer must be added to adjust the pH value, and finally a colorimetric reagent must be introduced for reaction. This multi-step operation is not only complex and time-consuming, but also introduces significant human error due to the multiple additions of reagents and control of reaction conditions, affecting the accuracy and repeatability of the results.

[0004] The trade-off between reagent cost and stability: Currently, commercially available reagent kits typically use aliquot packaging to mitigate inter-reagent interference and stability issues. However, this not only increases packaging and material costs but also adds space requirements for transportation and storage. Furthermore, end-users need to perform multiple preparation and sample addition steps for each test, which is not conducive to rapid screening and real-time monitoring in field or emergency environments.

[0005] Therefore, there is an urgent need in the industry to develop a pre-prepared solution, preparation method, and determination method for the determination of total iron in water that can be prepared at room temperature and integrates the three functions of reduction, color development, and buffering. This is intended to overcome the limitations of existing methods in terms of operability, stability, and applicability, and to improve the efficiency and reliability of iron ion detection. Summary of the Invention

[0006] The purpose of this invention is to provide a pre-prepared solution, preparation method, and determination method for the determination of total iron in water, aiming to solve the technical problems of cumbersome heating digestion, numerous steps, and long time consumption in traditional total iron determination methods.

[0007] To achieve the above-mentioned objectives, the first objective of this invention is to provide a pre-prepared solution for the determination of total iron in water, wherein each 1000 mL of the pre-prepared solution comprises: 45mL-55mL of concentrated hydrochloric acid; 9g-11g of hydroxylamine hydrochloride; 0.12g-0.18g of phenanthridine; The final system pH was adjusted to 4.5 ± 0.2 using an acetate-sodium acetate buffer. The remainder is deionized water.

[0008] Preferably, the concentration of concentrated hydrochloric acid is 50.0 mL, the concentration of hydroxylamine hydrochloride is 10.0 g, and the concentration of phenanthridine is 0.15 g.

[0009] A second objective of this invention is to provide a method for preparing a pre-prepared solution for the determination of total iron in water, wherein the method for preparing 1000 mL of the pre-prepared solution includes: S101. Place a plastic beaker containing 800mL of deionized water on a magnetic stirrer; turn on the magnetic stirrer. S102, add 45mL-55mL of concentrated hydrochloric acid; S103. Add 9-11g of solid hydroxylamine hydrochloride and stir continuously until the solid is completely dissolved and the solution is clear. S104. Add 0.12g-0.18g of solid phenanthridine and stir continuously for more than 30 minutes to completely dissolve the color developer. S105, add acetate-sodium acetate buffer; S106. Add deionized water to a final volume of 1000 mL and mix thoroughly.

[0010] Preferably, it also includes: S106, dispensing 5.00 mL per vial into transparent or brown glass / plastic tubes with rubber stoppers or threaded caps.

[0011] Preferably, the concentrated hydrochloric acid solid is 50.0 mL, the hydroxylamine hydrochloride solid is 10.0 g, and the phenanthridine solid is 0.15 g. Preferably, step S101 includes: placing a 2000 mL plastic beaker containing 800 mL of deionized water on a magnetic stirrer in a fume hood; turning on the magnetic stirrer and setting the speed to 300 rpm.

[0012] Preferably, S103 includes: adding 9g-11g of solid hydroxylamine hydrochloride, increasing the stirring speed to 600rpm, and continuing to stir for 15-20 minutes until the solid is completely dissolved and the solution is clear.

[0013] A third objective of this invention is to provide a method for determining total iron in water, comprising: S1. Add the pre-prepared liquid to the sample to be tested according to the predetermined volume ratio; S2. After mixing, react at room temperature for 10 minutes. S3. Measure the absorbance at a wavelength of 562 nm; S4. Calculate the original concentration based on the standard curve.

[0014] Preferably, based on the range of iron concentration, it is divided into: Standard mode: Applicable to water samples with iron concentration of 0.01 mg / L-10 mg / L. Take 10.0 mL of sample and add 5.0 mL of pre-prepared solution; Extended mode: Applicable to water samples with iron concentration of 2 mg / L-50 mg / L. Take 5.0 mL of sample, dilute with deionized water to 10 mL, and add 5.0 mL of pre-prepared solution.

[0015] Preferably, the method also includes the plotting of a standard curve: using the same volume ratio, prepare a series of standard irons of different concentrations with deionized water for color development, and plot a standard curve, requiring a correlation coefficient R² ≥ 0.99.

[0016] Compared with the prior art, the present invention has the following technical effects: This invention provides a chemically stable, single-solution pre-mixed reagent that premixes a strong acid extractant (such as concentrated hydrochloric acid), a highly efficient reducing agent (such as hydroxylamine hydrochloride), and an iron ion colorimetric agent (such as phenanthroline) in the same system. Through a specific buffer-stabilization system design, this premixed reagent can maintain an extremely low pH (typically below 1.0) during storage, thereby ensuring the long-term stability of each component without decomposition. When diluted with water, the pH of the system automatically rises to the optimal range required for the colorimetric reaction, thus enabling the automatic and continuous execution of the three-step reaction of acidolysis, reduction, and colorimetry without the need for external pH adjustment.

[0017] The corresponding determination method is extremely simple: just take a certain volume of water sample (e.g., 5.00 mL), add the corresponding proportion of premixed single reagent (e.g., 2.50 mL), mix well, and let stand at room temperature for 10 minutes. The reaction will be completely finished. The absorbance can be directly measured at a specific wavelength (e.g., 510 nm), and the result can be calculated based on the standard curve.

[0018] This invention simplifies the traditional multi-step process of "adding acid and heating—cooling—adding reducing agent—adding buffer—adding colorimetric agent" into a single-step process of "sampling—adding a single reagent—reading the value," significantly reducing the barrier to entry and the risk of operational errors. The total detection time is reduced from 30–40 minutes to less than 15 minutes. This premixed reagent exhibits good stability and can be stored at room temperature for at least six months. Its standard 2.50 mL single-use design, provided in ampoules or pre-filled tubes, avoids residue and dosage errors caused by adding multiple reagents in separate doses. It also reduces reliance on professional operators, resulting in lower operating and consumable costs.

[0019] In addition, this reagent system is highly portable, requires no refrigeration or special storage conditions, and can be widely used for rapid on-site detection and large-scale laboratory analysis, including but not limited to monitoring iron content in groundwater, rivers, lakes, drinking water and wastewater.

[0020] The chemical reaction involved in this invention is rapid and thorough, with highly specific colorimetric reactions that do not produce any side reactions or interfering substances, thus ensuring high accuracy and repeatability of the analytical results. Simultaneously, this method significantly reduces sample processing and instrument operation time, greatly improving detection efficiency. In summary, this invention achieves standardization of the detection process, automation of the operation procedure, portability of application scenarios, and cost-effectiveness in the field of water iron analysis, demonstrating clear technological innovation, significant practical value, and broad market application prospects. Attached Figure Description

[0021] Figure 1 This is a flowchart of the preparation method provided in a preferred embodiment of the present invention; Figure 2 The flowchart illustrates the measurement method provided in a preferred embodiment of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are only a part of the embodiments of the present invention, and not all of them. Generally, the embodiments of the present invention described and shown in the accompanying drawings are characteristic technologies and solutions. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0023] A first embodiment provides a pre-prepared solution for the determination of total iron in water, comprising: Each 1000 mL of pre-prepared solution includes: 45mL-55mL of concentrated hydrochloric acid; 9g-11g of hydroxylamine hydrochloride; 0.12g-0.18g of phenanthridine; The final system pH was adjusted to 4.5 ± 0.2 using an acetate-sodium acetate buffer. The remainder is deionized water.

[0024] For example: 50.0 mL of concentrated hydrochloric acid, 10.0 g of hydroxylamine hydrochloride, and 0.15 g of phenanthridine.

[0025] The pre-formulated solution in this invention is a heterogeneous suspension formed by sequentially dissolving specific chemical components at room temperature. The formulation mainly includes the following components: concentrated hydrochloric acid; hydroxylamine hydrochloride; ferrozine; an acetate-sodium acetate buffer, the amount of which must be sufficient to form and maintain an acidic environment of pH 4.5 ± 0.2 during the final dilution and color development stage; and deionized water.

[0026] During storage, the pre-prepared solution exists as a clear, acidic solution containing a large number of fine, undissolved buffer salt particles. These particles are evenly distributed and do not easily settle rapidly under static conditions, thus forming a suspension system with good stability, maintaining compositional homogeneity and functional consistency for a certain period of time.

[0027] Taking the preparation of 1000mL of this pre-prepared solution as an example, the specific content range of each component is as follows: Concentrated hydrochloric acid: 45mL–55mL; Hydroxylamine hydrochloride: 9g–11g; Ferrozine: 0.12g–0.18g; Acetic acid-sodium acetate buffer: The amount added should be adjusted to achieve a stable pH of 4.5. The specific amount should be adjusted slightly according to the buffering capacity of the actual batch. Deionized water: Add an appropriate amount to a total volume of 1000 mL.

[0028] The pre-prepared solution needs to be shaken well before use to ensure that the suspended particles are redispersed evenly, thereby ensuring the accuracy and repeatability of the test results.

[0029] The actual pH value of the pre-prepared solution is below 0.8 after preparation and standing equilibrium.

[0030] Under standard operating conditions, i.e., when the pre-prepared solution is mixed with the water sample at a volume ratio of 2:1 to 1:2, the pH of the final reaction system can be adjusted to the range of 4.5 ± 0.2.

[0031] The shelf life of the pre-prepared liquid under normal temperature and light-proof storage conditions shall not be less than 12 months.

[0032] The packaging unit is a brown glass bottle or polyethylene bottle, equipped with a screw cap with a PTFE liner.

[0033] This invention relates to a pre-mixed, chemically stable single solution specifically designed to simplify water quality testing procedures. This pre-mixed reagent maintains high stability during storage without being mixed with water samples, ensuring its long-term effectiveness and reliability. The pre-mixed solution contains the following key active ingredients in functional order: First, the pH control: By adding concentrated hydrochloric acid or concentrated nitric acid, the initial pH of the reaction system is strictly controlled below 0.8. This low pH environment effectively inhibits the colorimetric reaction of phenanthridine, thus keeping the colorimetric reagent in a "dormant" state during storage, preventing premature color development, and ensuring the shelf life and performance consistency of the reagent.

[0034] Secondly, the buffer-stabilizing system employs a buffer solution composed of sodium acetate and acetic acid, which exhibits excellent pH buffering capacity and chemical stability. When added to the acidic pretreatment solution, it not only helps maintain the stability of the system and prevents component degradation but also participates in pH adjustment in subsequent reactions, ensuring the controllability and repeatability of reaction conditions.

[0035] Finally, the single-liquid, one-step colorimetric mechanism: When the pre-prepared solution comes into contact with the water sample, hydroxylamine hydrochloride reacts rapidly to reduce the ferric ions in the sample, providing the necessary conditions for the colorimetric reaction. Simultaneously, the buffer reacts with the hydrochloric acid to neutralize it, automatically adjusting the system pH to approximately 4.5. This pH change activates the colorimetric function of phenanthroxazine, achieving a rapid and accurate colorimetric reaction. The entire process requires no additional steps or complex operations, greatly improving the convenience, efficiency, and accuracy of the detection.

[0036] Second embodiment, please refer to Figure 1 A method for preparing a pre-formulated solution for the determination of total iron in water, comprising: S101. In a fume hood, place a 2000mL plastic beaker containing 800mL of deionized water on a magnetic stirrer. Turn on the magnetic stirrer and set the speed to 300rpm.

[0037] S102. Add 50.0 mL of concentrated hydrochloric acid.

[0038] S103. Add 10.0g of hydroxylamine hydrochloride solid, increase the stirring speed to 600rpm, and continue stirring for 15-20 minutes until the solid is completely dissolved and the solution is clear.

[0039] S103. Add 0.15g of phenanthridine solid and stir continuously for at least 30 minutes to ensure that the color developer is completely dissolved.

[0040] S104. Add sufficient acetate-sodium acetate buffer.

[0041] S105. Make up to 1000 mL with deionized water and mix thoroughly.

[0042] S106. Accurately dispense 5.00 mL per vial into transparent or brown glass / plastic tubes with rubber stoppers or screw caps, seal, and store away from light. This is the premixed reagent for the determination of total iron in water.

[0043] Third embodiment, please refer to Figure 2 A method for determining total iron in water, comprising: S1. Add the pre-prepared liquid to the sample to be tested according to the predetermined volume ratio; S2. After mixing, react at room temperature for 10 minutes. S3. Measure the absorbance at a wavelength of 562 nm; S4. Calculate the original concentration based on the standard curve.

[0044] To better understand the technical solution of the present invention, the following non-limiting description is provided: This embodiment mainly includes the following steps: Step A, Standard Curve: The specific steps for plotting the standard curve are as follows: Using the same volume ratio, prepare standard iron series of different concentrations with deionized water for color development, and plot standard curves, requiring a correlation coefficient R² ≥ 0.99.

[0045] Step B, Sampling: Accurately measure a predetermined volume V (mL) of the water sample to be tested into a colorimetric tube, that is, take a certain amount (e.g., 10.0 ml) of water sample and place it into the colorimetric tube; Step C, single-step reagent addition: Add V mL (e.g., 5.00 ml) of pre-prepared solution to the water sample at the same time, immediately tighten the cap, shake well and let stand for 10 minutes; Step D, Mixing and Reaction: Immediately seal and thoroughly shake to mix. Allow to stand at room temperature (15℃-30℃) for approximately 10 minutes. During this process, the three steps of acid extraction, iron ion reduction, and colorimetric complexation occur sequentially and continuously automatically, requiring no intermediate steps.

[0046] Step E, Measurement: After the reaction is complete, measure the absorbance of the solution at the characteristic wavelength corresponding to the reagent using a spectrophotometer. This step can be performed using a portable spectrophotometer at a wavelength of 510 nm or by directly measuring the total iron concentration using a multi-parameter metal analyzer under iron program.

[0047] Step F, Result Calculation: Calculate the total iron concentration in the water sample based on the pre-established standard curve. This step compares the measured color depth or absorbance value with the pre-drawn standard curve using iron standard solution to calculate the total iron concentration in the water sample.

[0048] This invention provides two operating modes: Standard mode: Applicable to water samples with iron concentration of 0.01 mg / L-10 mg / L. Take 10.0 mL of sample and add 5.0 mL of pre-prepared solution; Extended mode: Applicable to water samples with iron concentration of 2 mg / L-50 mg / L. Take 5.0 mL of sample, dilute with deionized water to 10 mL, and add 5.0 mL of pre-prepared solution.

[0049] Performance verification, specifically including: S401, stability testing, specifically including: S4011. Place the prepared pre-mixed liquid in a 50℃ oven and heat for 7 days, simulating room temperature storage for 12 months.

[0050] S4012. After removal, cool to room temperature and add 1 mg / L standard iron solution to carry out a colorimetric reaction.

[0051] S4013, the initial absorbance changed from 0.183 to 0.181, RSD: 1.1%, proving excellent stability.

[0052] S402, Anti-interference capability verification, specifically including: Different interfering ions were added to water samples with known iron concentrations, and the recoveries were compared.

[0053] Original concentration: 1.00 mg / L.

[0054] Table 1 shows the experimental test parameters.

[0055] S403. Comparison with the national standard method, the results are as follows: Parallel measurements were performed on 30 water samples of different types (tap water, industrial circulating water, and industrial wastewater), and the results showed that the results obtained by this method were highly consistent with those of the national standard method.

[0056] Table 2 shows the comparison of results.

[0057] In one feasible technical solution, the chemical formulas used for the reaction in S2 include: Fe2O3+6H + →2Fe 3+ +3H2O [Fe-complex] + H + →Fe 3+ +[Protonated ligands] 2Fe 3+ +2NH₂OH·HCl→2Fe 2+ +N2↑+2H2O+4H + +2Cl - .

[0058] The above description is only a preferred embodiment of the present invention. It should be noted that any improvements, modifications, substitutions or variations made by those skilled in the art without departing from the principle of the present invention should be considered as being included within the protection scope of the present invention.

Claims

1. A pre-prepared solution for the determination of total iron in water, characterized in that, Each 1000 mL of pre-prepared solution includes: 45mL-55mL of concentrated hydrochloric acid; 9g-11g of hydroxylamine hydrochloride; 0.12g-0.18g of phenanthridine; The final system pH was adjusted to 4.5 ± 0.2 using an acetate-sodium acetate buffer. The remainder is deionized water.

2. The pre-prepared solution for total iron determination in water according to claim 1, characterized in that, The concentration of concentrated hydrochloric acid is 50.0 mL, hydroxylamine hydrochloride is 10.0 g, and phenanthridine is 0.15 g.

3. A method for preparing a pre-formulated solution for the determination of total iron in water, characterized in that, The preparation methods for each 1000 mL of pre-prepared solution include: S101. Place a plastic beaker containing 800mL of deionized water on a magnetic stirrer; turn on the magnetic stirrer. S102, add 45mL-55mL of concentrated hydrochloric acid; S103. Add 9-11g of solid hydroxylamine hydrochloride and stir continuously until the solid is completely dissolved and the solution is clear. S104. Add 0.12g-0.18g of solid phenanthridine and stir continuously for more than 30 minutes to completely dissolve the color developer. S105, add acetate-sodium acetate buffer; S106. Add deionized water to a final volume of 1000 mL and mix thoroughly.

4. The method for preparing the pre-prepared solution for total iron determination in water according to claim 3, characterized in that, Also includes: S106. Dispense 5.00 mL per vial into clear or brown glass / plastic tubes with rubber stoppers or threaded caps.

5. The pre-prepared solution for total iron determination in water according to claim 3, characterized in that, The solid concentration of concentrated hydrochloric acid is 50.0 mL, the solid concentration of hydroxylamine hydrochloride is 10.0 g, and the solid concentration of phenanthridine is 0.15 g.

6. The method for preparing the pre-formulated solution for total iron determination in water according to claim 3, characterized in that, S101 includes: placing a 2000mL plastic beaker containing 800mL of deionized water on a magnetic stirrer in a fume hood; turning on the magnetic stirrer and setting the speed to 300rpm.

7. The method for preparing the pre-formulated solution for total iron determination in water according to claim 6, characterized in that, S103 includes: adding 9g-11g of solid hydroxylamine hydrochloride, increasing the stirring speed to 600rpm, and stirring continuously for 15-20 minutes until the solid is completely dissolved and the solution is clear.

8. A method for determining total iron in water, characterized in that, include: S1. Add the pre-prepared liquid from claim 1 or 2 to the sample to be tested according to a predetermined volume ratio; S2. After mixing, react at room temperature for 10 minutes. S3. Measure the absorbance at a wavelength of 562 nm; S4. Calculate the original concentration based on the standard curve.

9. The method for determining total iron in water according to claim 8, characterized in that, Based on the range of iron concentration, it is divided into: Standard mode: Applicable to water samples with iron concentration of 0.01 mg / L-10 mg / L. Take 10.0 mL of sample and add 5.0 mL of pre-prepared solution; Extended mode: Applicable to water samples with iron concentration of 2 mg / L-50 mg / L. Take 5.0 mL of sample, dilute with deionized water to 10 mL, and add 5.0 mL of pre-prepared solution.

10. The method for determining total iron in water according to claim 8, characterized in that, It also includes the plotting of standard curves: using the same volume ratio, prepare a series of standard irons of different concentrations with deionized water for color development, and plot a standard curve, requiring a correlation coefficient R² ≥ 0.99.

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