Method for detecting iron content in sodium hypochlorite

Abstract

The invention relates to a method for detecting the iron content in sodium hypochlorite, and belongs to the technical field of analytical chemistry detection. The method comprises the following steps: adjusting the pH value of a sodium hypochlorite solution sample, sequentially adding a reducing agent and a buffer solution, and pre-treating the sodium hypochlorite sample to neutralize the strong oxidizing property of the sodium hypochlorite sample and adjust the pH value of the system; then adding a color developing agent to enable the iron ions to form a stable colored complex, finally determining the absorbance by adopting a spectrophotometer under a specific wavelength, and calculating the iron content through a standard curve. The method is simple and convenient to operate and high in adaptability, interference of oxidability and impurity metal ions can be effectively eliminated, the detection sensitivity, accuracy and repeatability are remarkably improved, and the method is suitable for quality control and conventional analysis of a high-purity sodium hypochlorite product.

Description

Technical Field

[0001] The invention relates to the technical field of chemical analysis and detection, and in particular to a method for detecting iron content in sodium hypochlorite. Background Art

[0002] Sodium hypochlorite is a commonly used, highly effective oxidizing disinfectant widely used in water treatment, industrial bleaching, medical sterilization, and food disinfection. To ensure product quality and safety, my country's national standard "GB 19106-2013 Sodium Hypochlorite" stipulates a limit for iron content and recommends a reduction method combined with colorimetric analysis for quantitative analysis. The current mainstream detection method involves adding hydrogen peroxide to eliminate the oxidizing properties of hypochlorite in the sample, then using a colorimetric reagent to generate a complexing reaction with the iron ions. Finally, spectrophotometry is used to measure absorbance and convert it into iron content.

[0003] However, in actual testing, the current standard method suffers from numerous technical flaws, leading to significant deviations in measurement results and poor reproducibility, seriously compromising analytical accuracy and reliability. First, the national standard uses the discoloration of starch-potassium iodide test paper as the basis for determining "complete removal of hypochlorite." However, experiments have shown that this determination is highly subjective. Even when the test paper appears colorless, residual hydrogen peroxide or other oxidizing substances may remain in the solution. These substances will further oxidize the developer or iron ions during the subsequent color development step, resulting in a low measured value. Second, hydrogen peroxide itself possesses both oxidizing and reducing properties, making its dosage extremely difficult to control. If the dosage is insufficient, hypochlorite is not fully reduced; if it is excessive, the excess hydrogen peroxide may react with the colored complex, resulting in a decrease in absorbance and measurement error. Spike recovery experiments have shown that the standard method often struggles to maintain a stable recovery within the acceptable range of 95% to 105%, indicating significant methodological limitations.

[0004] Therefore, there is an urgent need for a method for detecting the iron content in sodium hypochlorite that can eliminate oxidative interference and adjust the color reaction environment through effective pretreatment methods to achieve accurate, stable, and repeatable determination of trace iron ions in sodium hypochlorite. It is based on this background that the present invention proposes a novel method for detecting the iron content in sodium hypochlorite with multiple control mechanisms. While retaining the advantages of simple and efficient spectrophotometric analysis, the method significantly improves the stability, selectivity, and sensitivity of the method, making it suitable for routine industrial analysis and high-purity product quality control. Summary of the Invention

[0005] The object of the present invention is to provide a method for detecting the iron content in sodium hypochlorite to solve the problems raised by the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for detecting the iron content in sodium hypochlorite, which realizes the detection of the iron content in the sodium hypochlorite solution by optimizing the sample pretreatment process, the color reaction system and the spectrophotometric determination technology, and specifically comprises the following steps:

[0007] (1) Pre-treating the sodium hypochlorite solution sample, adjusting the pH of the sodium hypochlorite solution sample, and then sequentially adding a reducing agent and a buffer solution to neutralize the oxidizing property of the sodium hypochlorite, and adjusting the pH of the reaction environment to 4.0-6.0 to ensure a color reaction environment;

[0008] (2) adding a color developer to the pretreated sample to allow the iron ions in the sample to react specifically with the color developer to form a stable colored complex;

[0009] (3) Use a spectrophotometer to measure the absorbance of the sample at a specific wavelength, and quantitatively calculate the iron content in the sodium hypochlorite solution based on a pre-established standard curve of iron ion concentration and absorbance.

[0010] As a preferred technical solution of the present invention, the pretreatment in step (1) includes adjusting the pH of the sodium hypochlorite solution sample to destroy the stability of hypochlorite; adding a reducing agent to neutralize the oxidizing property of sodium hypochlorite to prevent it from oxidizing the developer or interfering with the color development reaction of iron ions; removing excess reducing agent hydrogen peroxide to prevent it from oxidizing the developer or interfering with the color development reaction of iron ions, thereby improving the sensitivity and accuracy of detection;

[0011] As a preferred technical solution of the present invention, an acidic solution, which is one of a sulfuric acid solution or a hydrochloric acid solution, is added in the pretreatment in step (1) to ensure that the pH value of the sample solution is lower than 1, so that sodium hypochlorite is converted into hypochlorous acid, thereby destroying the stability of sodium hypochlorite and facilitating its reaction with the reducing agent.

[0012] As a preferred technical solution of the present invention, the amount of acidic solution added in the pretreatment in step (1) is 1.0 to 2.0 times the amount of sodium hydroxide in the sample solution. After adding, stir for 1 to 2 minutes, and the sample solution can be observed to turn yellow.

[0013] As a preferred technical solution of the present invention, the reducing agent is one or a combination of sodium sulfite, sodium dithionite, ascorbic acid or hydrazine compounds (peroxides), and the amount added is 0.03 to 0.05 grams of reducing agent per milliliter of sodium hypochlorite solution. After addition, stirring is carried out at room temperature for 2 to 5 minutes.

[0014] As a preferred technical solution of the present invention, the reducing agent is one or a combination of sodium sulfite, sodium dithionite, ascorbic acid, or a hydrazine compound (peroxide). After the reducing agent completely reacts with the hypochlorous acid, the residual agent can be completely removed by heating.

[0015] As a preferred technical solution of the present invention, the pretreatment in step (1) further includes adding a buffer solution to adjust the pH of the sample solution to 4.0-6.0, providing a stable acidic environment, promoting the complexation reaction between iron ions and the developer, and avoiding the decomposition of the developer due to too low pH or the precipitation of iron ions due to too high pH.

[0016] As a preferred technical solution of the present invention, the buffer solution is acetic acid-sodium acetate buffer, citric acid-sodium citrate buffer or phosphoric acid-disodium hydrogen phosphate buffer, and its added amount is 0.5 to 1.0 times the volume of the sodium hypochlorite sample. After addition, stir for 1 to 2 minutes, and use a pH meter or pH test paper to verify whether the pH value is within the target range.

[0017] As a preferred technical solution of the present invention, the color developer in step (2) is one of 1,10-phenanthroline, potassium thiocyanate, 2,2'-bipyridine or salicylic acid, and the color developer is added in the form of an aqueous solution with a concentration of 0.1% to 10% (w / v), and the added amount is 0.2 to 0.3 times the volume of the sodium hypochlorite sample. After addition, the color reaction is completed by standing at 25±2°C for 5 to 10 minutes.

[0018] As a preferred technical solution of the present invention, the measuring wavelength of the spectrophotometer in step (3) is selected according to the type of developer, wherein:

[0019] When using 1,10-phenanthroline, the measurement wavelength is 510±5nm;

[0020] When potassium thiocyanate is used, the measurement wavelength is 480 ± 5 nm;

[0021] When using 2,2'-bipyridine, the measurement wavelength is 520 ± 5 nm;

[0022] Before measurement, the spectrophotometer was zeroed using a blank solution with the same pretreatment conditions as the sample, and the optical path was kept clean during the measurement.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention effectively addresses the problem of interference of strongly oxidizing substances in sodium hypochlorite samples with the iron color development reaction by introducing a multi-component collaborative pretreatment system. Through acid-base neutralization and optimized use of reducing agents, the oxidizing properties of sodium hypochlorite and its decomposition products are successfully removed, ensuring the valence stability of iron ions in the sample. The buffer precisely regulates the pH of the reaction system, providing a suitable acidic environment for the color development complexation reaction, significantly improving the accuracy, sensitivity, and repeatability of the assay.

[0025] The method of the present invention has good compatibility with colorimetric systems and is compatible with a variety of iron ion colorimetric reagents, including 1,10-phenanthroline, potassium thiocyanate, and 2,2'-bipyridine. The measurement wavelength range covers 480nm to 520nm, demonstrating good adaptability and versatility. Combinations of different pretreatment reagents can also be flexibly selected based on the impurity components in the sample, thereby adapting to the testing needs of sodium hypochlorite products from different sources and with different purity levels. Experimental results show that regardless of the combination used, stable spike recovery rates and absorbance repeatability can be achieved, demonstrating that the method maintains high reliability under a variety of technical conditions.

[0026] The method of the present invention is simple to operate, uses readily available reagents, and requires minimal equipment. It is particularly suitable for routine quality control, finished product inspection, and trace metal limit control in industrial production. Compared to the current standard method, this method not only avoids the uncertainty of hydrogen peroxide use but also significantly improves the repeatability and lower limit detection capability of iron content determination. It is particularly suitable for the quality evaluation of high-purity sodium hypochlorite products or electronic-grade disinfectants, where strict control of iron impurities is required. It has broad industrial practical value and promotion prospects. DETAILED DESCRIPTION

[0027] The present invention relates to a method for detecting iron content in a highly oxidizing environment using sodium hypochlorite. By systematically optimizing the sample pretreatment process, color development reaction system, and spectrophotometric measurement technology, this method can accurately and stably detect trace iron ions in complex oxidizing media. The entire method process includes five major steps: adjusting the pH of the sodium hypochlorite solution sample, destabilizing hypochlorite, eliminating oxidative interference, adjusting the system pH, complexation color development, and photometric measurement. Each step works in conjunction with each other to ensure the accuracy, sensitivity, and reproducibility of the measurement results.

[0028] During specific implementation, the sample is first pretreated. This method uses 20.00mL of sodium hypochlorite solution as the detection object, which is diluted to 500mL after weighing and thoroughly mixed to prepare test solution A. Take 50.00mL of test solution A and place it in a 250mL beaker. First, add a certain amount of acidic solution to ensure that the sodium hypochlorite in the solution is converted into hypochlorous acid. Then, add a reducing agent to neutralize the strong oxidizing properties of the sample itself. Reducing agents that can be used include sodium sulfite, sodium dithionite, ascorbic acid or hydrazine compounds / peroxides, etc. Through redox reactions, hypochlorite ions and their decomposition products are converted into non-interfering substances, thereby eliminating their possible destructive effects on subsequent color development reactions. In the experiment of the present invention, hydrogen peroxide is selected as a representative. The amount of reducing agent added is controlled to be 20% to 30% excess after the sodium hypochlorite solution is completely reacted. After addition, it is fully stirred at room temperature for 2 to 5 minutes. When the color of the solution gradually changes from light yellow to colorless or slightly lighter, the treatment is completed. Then, the sample solution is boiled for 10 minutes to remove excess hydrogen peroxide in the solution.

[0029] After the sample solution is treated, the pH value of the reaction system needs to be adjusted to ensure that the iron ions and the color developer can stably complex under appropriate conditions. This method uses a buffer solution to adjust the acidity and alkalinity of the system, and the pH is preferably controlled between 4.0 and 6.0. Within this range, the hydrolysis and precipitation of iron ions can be prevented, and the structural stability of the color developer can be maintained. The type of buffer solution can be selected from acetic acid-sodium acetate, citric acid-sodium citrate or phosphoric acid-disodium hydrogen phosphate buffer systems, and the amount added is 0.5 to 1.0 times the sample volume. Usually, after the buffer solution is added and stirred for 1 to 2 minutes, the final pH is measured by pH paper or pH meter to determine whether it meets the standard. If it is not within the target range, a small amount of buffer component can be added for fine-tuning.

[0030] After completing the above pretreatment process, the color development stage begins. Depending on the experimental purpose, the color developer can be selected from 1,10-phenanthroline, potassium thiocyanate, 2,2'-bipyridine, or salicylic acid, all of which are commonly used highly selective complexing agents for iron ions. The present invention uses 1,10-phenanthroline as an example. A 1% (w / v) aqueous solution is added to the sample solution at a ratio of 0.2 to 0.3 times the sample volume. The solution is then allowed to react at 25±2°C for 5 to 10 minutes. During this time, the solution gradually turns orange-red, indicating that Fe2+ and 1,10-phenanthroline form a tridentate stable complex [Fe(phen)3]2+. This complex has a distinct absorption peak at a wavelength of 510 nm. If a color developer such as potassium thiocyanate or 2,2'-bipyridine is used instead, the corresponding measurement wavelength should be adjusted to 480±5 nm or 520±5 nm, and the colorimetric reaction should be performed using the same method as above.

[0031] After the color development reaction is complete, the photometric measurement phase can begin. A spectrophotometer is used to read the absorbance, and a blank solution prepared under the same pretreatment conditions as the sample is used for zero adjustment to ensure baseline consistency. Using a 3cm pathlength cuvette, the sample absorbance is read at the target wavelength. Combined with a pre-drawn iron ion standard curve, the iron concentration in the sample can be accurately calculated.

[0032] To verify the detection effect and data stability of this method, multiple parallel samples were used for repeated testing, and a 0.02 mg iron standard solution was introduced for spike recovery testing. The following are some experimental results using the 1,10-phenanthroline color development conditions of the present invention:

[0033]

[0034]

[0035] It can be seen that this method showed excellent reproducibility in different samples, with extremely small absorbance deviation and spiked recoveries within a reasonable range, indicating that the pretreatment measures used effectively eliminated oxidation interference and metal competition interference.

[0036] In another experiment, potassium thiocyanate was used as the color developer, sodium dithionite as the reducing agent, tartaric acid as the masking agent, and a citric acid system as the buffer. The results also showed good response sensitivity. Some of the experimental data are as follows:

[0037]

[0038] The above results further verified that this method has good repeatability and stability under different pretreatment conditions and colorimetric reagent systems, and is suitable for trace iron ion detection scenarios in various sodium hypochlorite-derived samples.

[0039] In summary, the detection method described in the present invention is simple to operate, uses universal reagents, and has a low detection limit. It can significantly improve the sensitivity, selectivity, and accuracy of iron content determination and is suitable for quality monitoring, purity testing, and related process control of industrial sodium hypochlorite products. This method can accurately quantify the iron content in sodium hypochlorite samples to below 0.00005%, significantly compensating for the poor adaptability of current standard methods in high-purity systems and possessing broad engineering applications and promotional value.

[0040] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for detecting iron content in sodium hypochlorite, characterized in that, This method realizes the detection of iron content in sodium hypochlorite by optimizing the sample pretreatment process, color reaction system and spectrophotometric determination technology, and specifically includes the following steps: (1) Pre-treating the sodium hypochlorite solution sample by adjusting the pH of the sodium hypochlorite solution sample, then sequentially adding a reducing agent and a buffer solution to neutralize the oxidizing property of the sodium hypochlorite and adjusting the pH of the reaction system to 4.0-6.0; (2) adding a color developer to the pretreated sample to allow the iron ions in the sample to react specifically with the color developer to form a stable colored complex; (3) Use a spectrophotometer to measure the absorbance of the sample at a specific wavelength, and quantitatively calculate the iron content in the sodium hypochlorite solution based on a pre-established standard curve of iron ion concentration and absorbance.

2. The detection method according to claim 1, wherein The pretreatment in step (1) includes adjusting the pH of the sodium hypochlorite solution sample to destroy the stability of hypochlorite; adding a reducing agent to neutralize the oxidizing property of sodium hypochlorite to prevent it from oxidizing the color developer or interfering with the color development reaction of iron ions; and removing excess reducing agent that interferes with the color development reaction of iron ions, thereby improving the sensitivity and accuracy of detection.

3. The detection method according to claim 2, characterized in that An acidic solution, which is one of a sulfuric acid solution or a hydrochloric acid solution, is added in the pretreatment in step (1) to ensure that the pH value of the sample solution is lower than 1, so that sodium hypochlorite is converted into hypochlorous acid, thereby destroying the stability of sodium hypochlorite and making it easy to react with the reducing agent.

4. The detection method according to claim 2, characterized in that The amount of acidic solution added in the pretreatment in step (1) is 1.0 to 2.0 times the amount of sodium hydroxide in the sample solution. After adding, stir for 1 to 2 minutes, and the sample solution can be observed to turn yellow.

5. The detection method according to claim 2, characterized in that The reducing agent is one of sodium sulfite, sodium dithionite, ascorbic acid or hydrazine compounds or a combination thereof, and is added in an amount of 0.03 to 0.05 grams per milliliter of sodium hypochlorite solution, and stirred at room temperature for 2 to 5 minutes after addition.

6. The detection method according to claim 2, characterized in that The reducing agent is one of sodium sulfite, sodium dithionite, ascorbic acid or hydrazine compounds or a combination thereof, and after the reducing agent reacts completely with the hypochlorous acid, the residual reagent can be completely removed by heating.

7. The detection method according to claim 1, characterized in that The pretreatment in step (1) further includes adding a buffer solution to adjust the pH of the sample solution to 4.0-6.0, providing a stable acidic environment to promote the complexation reaction between the iron ions and the developer, while avoiding the decomposition of the developer due to too low a pH or the precipitation of iron ions due to too high a pH.

8. The detection method according to claim 4, characterized in that The buffer solution is acetic acid-sodium acetate buffer, citric acid-sodium citrate buffer or phosphoric acid-disodium hydrogen phosphate buffer, and its added amount is 0.5 to 1.0 times the volume of the sodium hypochlorite sample. After addition, it is stirred for 1 to 2 minutes, and a pH meter or pH test paper is used to verify whether the pH value is within the target range.

9. The detection method according to claim 1, wherein The color developer in step (2) is one of 1,10-phenanthroline, potassium thiocyanate, 2,2'-bipyridine or salicylic acid. The color developer is added in the form of a 0.1% to 10% (w / v) aqueous solution, and the added amount is 0.2 to 0.3 times the volume of the sodium hypochlorite sample. After addition, the solution is allowed to stand at 25±2° C. for 5 to 10 minutes to complete the color development reaction.

10. The detection method according to claim 1, characterized in that The measuring wavelength of the spectrophotometer in step (3) is selected according to the type of developer, wherein: When using 1,10-phenanthroline, the measurement wavelength is 510±5nm; When potassium thiocyanate is used, the measurement wavelength is 480 ± 5 nm; When using 2,2'-bipyridine, the measurement wavelength is 520 ± 5 nm; Before measurement, the spectrophotometer was zeroed using a blank solution with the same pretreatment conditions as the sample, and the optical path was kept clean during the measurement.

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