A method for pretreatment conversion and electrochemical synchronous detection of inorganic arsenic and total mercury in rice

Abstract

The application belongs to the technical field of food safety detection, heavy metal detection and electrochemical analysis, and specifically comprises a pretreatment conversion and electrochemical synchronous detection method for inorganic arsenic and total mercury in rice. The electrochemical synchronous detection method comprises: adding an acid oxidation extraction liquid to the rice powder to be detected, heating and ultrasonicating, so that arsenic and mercury are fully released from the rice matrix and part of the arsenic and mercury is converted into As(V) and Hg(II), centrifuging to obtain an extraction liquid; adding a composite reducing agent to the extraction liquid to further reduce As(V) in the extraction liquid into As(III) to obtain a detection liquid; using an electrochemical method to test the content of As(III) and Hg(II) in the detection liquid to determine the content of inorganic arsenic and total mercury in the rice to be detected; wherein the acid oxidation extraction liquid comprises inorganic acid and persulfate oxidant, and the composite reducing agent comprises sulfite and / or hydroxylamine salt. The detection method can synchronously detect the content of inorganic arsenic and total mercury in the rice sample, and has the characteristics of rapidness, sensitivity and low cost.

Description

Technical Field

[0001] This invention belongs to the field of food safety testing, heavy metal detection and electrochemical analysis technology, specifically including a method for pretreatment conversion and simultaneous electrochemical detection of inorganic arsenic and total mercury in rice. Background Technology

[0002] Rice is one of the most important food crops in the Chinese diet. During its growth, it easily absorbs and accumulates toxic elements such as arsenic and mercury from the soil, irrigation water, and agricultural environment. Arsenic in rice typically exists in various forms, including inorganic and organic arsenic, with inorganic arsenic, especially trivalent arsenic, being highly toxic. Mercury can exist in forms such as divalent mercury and methylmercury (MeHg(I)), with MeHg(I) exhibiting strong bioaccumulation and neurotoxicity. Long-term consumption of rice containing arsenic and mercury may pose potential health risks. Therefore, establishing a rapid and accurate method for detecting inorganic arsenic and total mercury in rice samples is of great significance for food security supervision and pollution risk screening.

[0003] Currently, the main methods for detecting arsenic and mercury in food include atomic fluorescence spectrometry, inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectrometry, and liquid chromatography-ICP-MS. These methods have high sensitivity and accuracy, meeting the needs of laboratory confirmatory analysis. However, these methods typically rely on large instruments, involve complex sample pretreatment processes, have high detection costs, long detection cycles, and require highly skilled operators and specific experimental conditions, making them difficult to meet the needs of grassroots supervision, on-site screening, or rapid batch detection.

[0004] Regarding the extraction and detection of arsenic in grain or rice samples, existing technologies have yielded relevant research and reports. CN116413092A discloses a method for the extraction and detection of inorganic arsenic in grains. This method extracts inorganic arsenic from grain samples using inorganic acids and reducing agents, and then performs detection using a gold-plated screen-printed electrode. This method has some reference value for the rapid detection of inorganic arsenic in grains, but its main target is inorganic arsenic, and it does not involve the simultaneous extraction of mercury, the conversion of MeHg(I) to Hg(II), or the simultaneous detection of arsenic and mercury. Furthermore, there is still room for improvement in its extraction efficiency for inorganic arsenic in complex grain samples, and in the systematic comparison between the detection results and reference methods or actual sample values. CN110411805A discloses a method utilizing... L A rapid and green pretreatment method for extracting mercury speciation from grains using cysteine ​​can achieve rapid extraction of inorganic mercury and MeHg(I) from grains under relatively mild conditions. This method is suitable for mercury speciation preservation and analysis, but it does not address the simultaneous extraction and valence state control of arsenic, nor has it established a simultaneous arsenic and mercury detection system integrated with rapid electrochemical detection. Furthermore, LWhile cysteine ​​at certain concentrations is beneficial for the complexation and stabilization of mercury, excessive amounts... L -Cysteine ​​may have a masking effect on the electrochemical dissolution signals of mercury and arsenic.

[0005] Electrochemical detection offers advantages such as low cost, simple operation, fast response, and portability, making it suitable for rapid detection of heavy metals in food. For example, Talanta 153 (2016) 99-106 has reported on the simultaneous electrochemical detection of As(III) and Hg(II), but these studies primarily focus on relatively simple systems such as standard solutions, spiked water, or wastewater, typically targeting As(III) and Hg(II) already in electrochemically active forms. In contrast, rice matrices are complex, and arsenic and mercury often exist in multiple valence states, bound states, or organic forms. Without effective extraction, form transformation, and valence state regulation, directly using existing electrochemical simultaneous detection methods is insufficient to accurately reflect the content of inorganic arsenic and total mercury in the sample.

[0006] Meanwhile, when arsenic and mercury are simultaneously detected electrochemically in the same system, they may be affected by competitive deposition, complexation reactions, mutual influence of peak signals, and interference from the complex matrix of rice, leading to a decrease in detection accuracy and reproducibility. Existing methods for detecting inorganic arsenic and total mercury typically require strong acid digestion or large-scale instrument analysis, and existing electrochemical methods often lack conversion systems suitable for the pretreatment of complex grain samples. Therefore, developing a method applicable to the complex matrix of rice that simultaneously extracts arsenic and mercury, converts MeHg(I) to Hg(II), regulates arsenic valence state, and enables simultaneous electrochemical detection is of great significance for improving the rapid screening capability of inorganic arsenic and total mercury in rice. Summary of the Invention

[0007] To address the problems of complex pretreatment of rice samples, long detection cycles, difficulty in simultaneous and rapid detection of inorganic arsenic and total mercury, and insufficient adaptability of arsenic and mercury speciation conversion in complex rice matrices to electrochemical detection systems, this invention aims to provide a pretreatment conversion and simultaneous electrochemical detection method for inorganic arsenic and total mercury in rice. The detection method includes pretreatment suitable for the simultaneous release of arsenic and mercury in rice samples, conversion of organic mercury such as MeHg(I) in rice samples, regulation of arsenic reduction valence state, and simultaneous electrochemical detection, achieving rapid, sensitive, and low-cost simultaneous detection of inorganic arsenic and total mercury in rice samples.

[0008] To achieve the above objectives, the technical solution adopted by the present invention includes: This invention discloses a method for pretreatment conversion and simultaneous electrochemical detection of inorganic arsenic and total mercury in rice, comprising the following steps: S1. Add acidic oxidative extract to the rice flour to be tested, heat and sonicate to fully release arsenic and mercury from the rice matrix and convert some of the arsenic and mercury into As(V) and Hg(II), centrifuge to obtain the extract; In step S1, acidic oxidative extract is used to extract arsenic and mercury from rice, which can release arsenic and mercury from rice flour sample from rice matrix. At the same time, organic mercury forms such as MeHg(I) are oxidized and demethylated and converted into Hg(II). The extractable arsenic forms (i.e. inorganic arsenic) in the sample are mainly converted into As(V) after oxidation treatment. S2. Add a composite reducing agent to the extract to further reduce As(V) in the extract to As(III) to obtain the test solution; Step S2 is a valence state control step, which further reduces the arsenic form in the extract, mainly As(V), to As(III), and makes the total mercury exist stably in the test system mainly in the electrochemically responsive form of Hg(II), thereby realizing the electrochemical response normalization detection of inorganic arsenic and total mercury. After the above pretreatment and conversion are completed, the test system contains As(III) and Hg(II) forms suitable for electrochemical detection, and then the electrochemical simultaneous detection in step S3 is performed. S3. The contents of As(III) and Hg(II) in the test solution are tested by electrochemical methods to determine the contents of inorganic arsenic and total mercury in the rice to be tested; The acidic oxidative extract includes inorganic acids and persulfate oxidants, and the composite reducing agent includes sulfites and / or hydroxylamine salts.

[0009] Furthermore, the inorganic acid is hydrochloric acid, and the persulfate oxidant is potassium persulfate and / or ammonium persulfate, preferably potassium persulfate.

[0010] Furthermore, the volume fraction of the inorganic acid is 1-10%; for example, the volume fraction of the inorganic acid can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., preferably 5%.

[0011] Furthermore, the mass fraction of the persulfate oxidant is 0.5-4%; for example, the mass fraction of the persulfate oxidant can be 0.5%, 1%, 2%, 3%, 4%, etc., preferably 1%.

[0012] Furthermore, in step S1, the ultrasonic temperature is 50-85 ℃, preferably 75 ℃, and the ultrasonic time is 3-15 min, preferably 10 min.

[0013] Furthermore, the mass-to-volume ratio of the rice flour to be tested to the acidic oxidative extract is 1 g / 5 mL to 0.2 g / 5 mL.

[0014] To further promote the release of arsenic and mercury from the rice matrix and ensure their stable presence in the extract, while reducing mercury re-adsorption loss, a complexing extractant is added to the system before centrifugation in step S1, and optionally, sonication is performed to achieve complexation stabilization of arsenic and mercury in the system.

[0015] Furthermore, the complexing extractant is selected from... L -cysteine, L One or more of cysteine ​​hydrochloride, mercaptoacetic acid, and mercaptoethanol, preferably L -Cysteine.

[0016] Furthermore, the concentration of the complexing extractant in the system is 0.5-5 mM; for example, the concentration of the complexing extractant in the system can be 0.5 mM, 1 mM, 2 mM, 3 mM, 4 mM, 5 mM, etc., preferably 2 mM.

[0017] Furthermore, the conditions for ultrasonication after adding the complexing extractant are: temperature of 50-85 ℃, preferably 75 ℃, and ultrasonication time of 1-5 min, preferably 1 min.

[0018] Furthermore, the sulfite is sodium sulfite, and the hydroxylamine salt is hydroxylamine hydrochloride.

[0019] Furthermore, the composite reducing agent is a composite reducing system composed of sodium sulfite and hydroxylamine hydrochloride.

[0020] Furthermore, the concentration of sulfite in the extract is 0.01-0.2 g / L, preferably 0.05 g / L.

[0021] Furthermore, the concentration of the hydroxylamine salt in the extract is 0.1-1.0 g / L, preferably 0.5 g / L.

[0022] Furthermore, the rice flour to be tested can be selected from actual rice flour samples, arsenic and mercury-valued rice flour samples, rice standard reference materials, blank rice matrix samples, or blank spiked rice matrix samples. The standard materials used for method validation include, but are not limited to, arsenic single-element solution standard materials, mercury single-element solution standard materials, MeHg(I) single-element solution standard materials, and rice blank matrix standard materials. Preferably, the standard materials include GBW08611 arsenic single-element solution standard materials, GBW08617 mercury single-element solution standard materials, GBW08675 MeHg(I) single-element solution standard materials, and the rice blank sample METAL-DJTZK-50 standard material.

[0023] Of course, during steps S1 and S2, standard solutions of arsenic and mercury can be prepared to form reference solutions, and blank rice matrix samples can be used for blank spiked addition to prepare blank spiked control sample test solutions. These solutions are used to evaluate the extraction efficiency, valence conversion efficiency, and recovery rate of different forms of arsenic and mercury in rice samples during steps S1 and S2. Furthermore, inductively coupled plasma mass spectrometry (ICP-MS) can be used to compare and verify the inorganic arsenic content in the test samples; a mercury analyzer can be used to compare and verify the total mercury content in the test samples; and liquid chromatography-inductively coupled plasma mass spectrometry (LC-ICP-MS) can be used to compare and verify the speciation and valence conversion results of arsenic and mercury in the test samples.

[0024] Furthermore, step S3 further includes: The test solution and electrolyte were mixed, and a gold-modified screen-printed carbon electrode was used as the working electrode. The gold-modified screen-printed carbon electrode was placed in the above mixed solution, and anodic stripping voltammetry was used for detection. As(III) and Hg(II) were enriched on the surface of the gold-modified screen-printed carbon electrode, and corresponding stripping peaks were generated during the anodic scanning process. Based on the current values ​​of the As(III) and Hg(II) stripping peaks, the contents of inorganic arsenic and total mercury in the rice to be tested were calculated.

[0025] Furthermore, the nano-gold modified screen-printed carbon electrode is prepared according to the following steps: A screen-printed carbon electrode is placed in a nano-gold deposition solution containing a gold precursor. After electrodeposition, a nano-gold modification layer is formed on the surface of the screen-printed carbon electrode, which is then obtained as a nano-gold modified screen-printed carbon electrode, denoted as Au@SPCE. The gold-containing precursor includes chloroauric acid, chloroaurate or their hydrates, preferably trichloroauric acid hydrate or tetrachloroauric acid hydrate; The supporting electrolyte in the nano-gold deposition solution is an acidic supporting electrolyte, preferably sulfuric acid, hydrochloric acid or nitric acid, and more preferably sulfuric acid.

[0026] Furthermore, the concentration of the gold-containing precursor in the gold nanoparticle deposition solution is 0.05-1 mM; for example, the concentration of the gold-containing precursor in the gold nanoparticle deposition solution can be 0.05 mM, 0.1 mM, 0.2 mM, 0.3 mM, 0.4 mM, 0.5 mM, 0.6 mM, 0.7 mM, 0.8 mM, 0.9 mM, 1 mM, etc., preferably 0.1 mM.

[0027] Furthermore, the electrodeposition includes constant potential deposition, constant current deposition, or cyclic voltammetric deposition, preferably constant potential deposition.

[0028] Furthermore, the deposition potential of the constant potential deposition is -0.6 to -1.1 V, preferably -0.8 to -1.0 V, and more preferably -1.0 V.

[0029] Furthermore, the anodic stripping voltammetry method includes linear scanning anodic stripping voltammetry, differential pulse anodic stripping voltammetry, or square wave anodic stripping voltammetry, preferably linear scanning anodic stripping voltammetry.

[0030] Furthermore, the enrichment potential set in the linear scanning anodic stripping voltammetry is -0.4 to -1.0 V, preferably -0.5 to -0.8 V, and more preferably -0.6 V; the enrichment time set in the linear scanning anodic stripping voltammetry is 120-360 s, preferably 300 s.

[0031] Further, the volume ratio of the test solution to the electrolyte is 100-400:600-900. In one specific embodiment, 100-400 mL of the test solution is mixed with 600-900 mL of electrolyte to obtain a mixed solution with a total volume of 1 mL. More preferably, 200 mL of the test solution is mixed with 800 mL of electrolyte to obtain a mixed solution.

[0032] In the above-mentioned simultaneous electrochemical detection method for arsenic and mercury, standard curves between concentration and dissolution peak current can be established using standard solutions of As(III) and Hg(II) at different concentrations. The content of inorganic arsenic and total mercury in rice samples can be calculated using the standard curve method or the standard addition method. For rice samples with strong matrix effects, the standard addition method is preferred for quantification. Furthermore, blank spiked control samples can be prepared by adding blank rice matrix samples to evaluate the extraction efficiency, valence conversion efficiency, and recovery rate of the pretreatment conversion method for different forms of arsenic and mercury in rice samples. The content of inorganic arsenic and total mercury in the test samples can also be compared and verified using ICP-MS and a mercury analyzer, and the speciation and valence conversion results of arsenic and mercury in the test samples can be compared and verified using LC-ICP-MS.

[0033] Furthermore, the electrolyte is sulfuric acid, hydrochloric acid, nitric acid, or sodium acetate-chloroacetic acid (pH=3), preferably sulfuric acid; the sulfuric acid concentration is 0.5-1.25 M, and for example, the concentration can be 0.5 M, 0.75 M, 1 M, 1.25 M, preferably 1.0 M.

[0034] Through the above technical solutions, the present invention can achieve the simultaneous release of arsenic and mercury in rice samples, the oxidation and transformation of mercury forms, the regulation of arsenic valence state, and the adaptation of the electrochemical detection system in a short time. This enables inorganic arsenic to enter the electrochemical detection system in the form of As(III) response and total mercury in the form of Hg(II) response. Combined with nano-gold modified screen-printed carbon electrodes, the invention achieves the simultaneous, rapid, and sensitive detection of inorganic arsenic and total mercury in rice.

[0035] Beneficial effects of this invention: This invention provides a method for the pretreatment conversion and simultaneous electrochemical detection of inorganic arsenic and total mercury in rice, which has the following advantages compared with the prior art: (1) To achieve effective extraction of different forms of arsenic and mercury from rice samples and unified control of their valence states.

[0036] This invention utilizes an acidic oxidative extraction system, a complexing extractant, and a composite reducing agent to effectively release arsenic and mercury from rice samples into the extractant, while also converting and regulating different forms of arsenic and mercury. Specifically, the acidic oxidative extraction system promotes the release of arsenic and mercury from the rice matrix, causing organic mercury forms such as MeHg(I) to undergo oxidative demethylation and convert to Hg(II), while extractable arsenic forms are primarily converted to As(V) after oxidation. Subsequently, the composite reducing agent regulates the valence state, reducing As(V) to As(III) suitable for anodic stripping voltammetry detection, while simultaneously ensuring that mercury exists stably in the strongly electrochemically responsive Hg(II) form. Therefore, this invention enables the simultaneous electrochemical detection of inorganic arsenic and total mercury in rice samples, after oxidation and reduction treatment, primarily in the As(III) responsive form. This method solves the problem that arsenic and mercury in rice samples have complex forms and different electrochemical responses, making direct and simultaneous detection difficult. It provides a stable and clear target for the subsequent simultaneous electrochemical detection of inorganic arsenic and total mercury.

[0037] (2) The pretreatment conditions are relatively mild and easy to operate, and can improve the response stability in the simultaneous detection of arsenic and mercury.

[0038] The pretreatment process of this invention does not rely on complex equipment such as high-temperature, high-pressure sealed digestion or microwave digestion. It can complete the extraction, oxidation conversion, complexation stabilization, and reduction of arsenic and mercury in rice samples under relatively mild conditions. It has the advantages of simple operation steps, small reagent consumption, short processing time, and suitability for batch sample processing. Simultaneously, this invention constructs an integrated technical system combining acidic oxidation extraction, complexation stabilization, composite reduction, and detection using a nano-gold modified electrode. Specifically, the pretreatment system can convert arsenic and mercury in rice samples into target response forms suitable for electrochemical detection; the nano-gold modified layer has good conductivity, a large effective active area, and the ability to enrich As(III) and Hg(II), which can enhance the deposition and dissolution response of these two substances on the electrode surface. Furthermore, by combining the composite reduction system with the nano-gold modified electrode detection system, this invention helps to improve the electrochemical response stability of As(III) and Hg(II) in the same detection system, reduce the effects of peak current suppression, peak position shift or signal masking that may occur during synchronous detection, and improve the resolution and detection stability of arsenic and mercury dissolution peaks, thereby providing technical support for the synchronous detection of inorganic arsenic and total mercury in a single injection.

[0039] (3) Simultaneous detection of inorganic arsenic and total mercury in rice is achieved, and the detection results are reliable.

[0040] This invention employs a gold-modified screen-printed carbon electrode as the working electrode and combines it with anodic stripping voltammetry to detect the pretreated test solution. In the test solution treated by this invention, inorganic arsenic is predominantly in the As(III) response form, while total mercury is predominantly in the Hg(II) response form. As(III) and Hg(II) can be enriched on the surface of the gold-modified screen-printed carbon electrode and produce distinguishable stripping peaks during anodic scanning. Based on the peak current values ​​corresponding to As(III) and Hg(II), the contents of inorganic arsenic and total mercury in the rice sample can be calculated separately, thereby achieving simultaneous detection of inorganic arsenic and total mercury in a single injection within the same system. Furthermore, the detection results of this invention can be verified through various auxiliary methods. For example, standard curves can be established using As(III) and Hg(II) standard solutions, and the accuracy, recovery rate, and precision of the method can be evaluated using rice samples with arsenic and mercury fixed values, blank rice matrix samples, and blank spiked samples. The results of inorganic arsenic and total mercury measured by this invention can also be compared with the results of ICP-MS and mercury analyzers, and the results of arsenic and mercury speciation or valence state transformation can be compared with the results of LC-ICP-MS coupled technology, thereby verifying the accuracy, reliability, and applicability of the method of this invention in the detection of actual rice samples.

[0041] (4) It is low in cost and simple to operate, and has the potential to be used for rapid screening and portable testing of rice samples.

[0042] This invention uses a screen-printed carbon electrode as the substrate electrode and prepares a nano-gold modification layer by electrodeposition. The electrode preparation method is simple, low-cost, and easy to mass-produce. Meanwhile, the invention consumes less sample and reagents during the detection process, and the pretreatment and detection operations are relatively simple. It can be used in conjunction with miniaturized or portable electrochemical detection equipment, eliminating the need for large instruments such as ICP-MS as detection readout devices. Furthermore, this invention can simultaneously detect inorganic arsenic and total mercury in rice samples within the same detection system, reducing the sample processing and detection steps required for separate detection and improving detection efficiency. Therefore, this invention has good potential for rapid screening and portable detection applications, and is suitable for food safety supervision, grassroots testing, and rapid on-site or near-site screening of arsenic and mercury contamination in rice samples. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the simultaneous detection process of arsenic and mercury in rice samples according to the present invention.

[0044] Figure 2 shows the LC-ICP-MS images of mercury and arsenic valence state transformation during the pretreatment process. In Figure 2, A represents the mercury morphology transformation under different acidic oxidative extraction conditions, and B represents the arsenic and mercury morphology changes before and after oxidative extraction and combined reduction treatment.

[0045] Figure 3 shows the optimization diagram of the composite reduction system and electrochemical detection conditions. In Figure 3, A shows the effect of different reduction systems on the reduction effect of As(V) and the simultaneous electrochemical detection signals of Hg(II) and As(III). In Figure 3, B shows the effect of different detection electrolyte systems on the simultaneous dissolution signals of As(III) and Hg(II). In Figure 3, C shows the effect of sulfuric acid concentration on the response signals of As(III) and Hg(II).

[0046] Figure 4 shows the simultaneous electrochemical detection signals and linear relationships of As(III) and Hg(II) in the spiked blank rice matrix sample. In Figure 4, A represents the fixed As(III) concentration of 100. g / L, Hg(II) concentration in the range of 1-300 g / L The synchronous detection signal and linear relationship when increasing within the range of g / L; B in Figure 4 is the fixed Hg(II) concentration of 100 g / L. g / L, As(III) concentration between 1-300 g / L The synchronous detection signal and linear relationship when As(III) and Hg(II) concentrations increase simultaneously within the range of g / L; C in Figure 4 represents the synchronous detection signal and linear relationship when As(III) and Hg(II) concentrations increase simultaneously (1-300 g / L). Synchronous detection signal and linear relationship (g / L). Detailed Implementation

[0047] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. It should be understood that the described embodiments are merely some, not all, of the embodiments of the present 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.

[0048] Figure 1 As shown, this invention provides a method for the pretreatment conversion and simultaneous electrochemical detection of inorganic arsenic and total mercury in rice, comprising two parts: rice sample pretreatment and electrochemical detection. After acidic oxidation extraction, arsenic and mercury in the rice sample are released from the rice matrix. The extractable arsenic forms are mainly converted to As(V) after oxidation treatment, and organic mercury such as MeHg(I) is converted to Hg(II) after demethylation oxidation. Subsequently, a complexation extraction / stabilization treatment is performed to obtain an extract containing Hg(II) and mainly As(V), with a small amount of As(III). Then, a composite reduction treatment is performed to further convert the arsenic forms, mainly As(V), to As(III), and to make the total mercury exist stably in the test system mainly in the form of Hg(II) with a strong electrochemical response, thereby achieving electrochemical response normalization detection of inorganic arsenic content in rice samples. The reduction system used in the composite reduction treatment achieves the conversion of As(V) to As(III) without significantly masking or interfering with the electrochemical responses of Hg(II) and As(III). During detection, a screen-printed carbon electrode is electrodeposited using a deposition solution containing Au(III) precursor to prepare a gold-modified screen-printed carbon electrode (Au@SPCE). The dissolution responses of Hg(II) and As(III) in the test solution are simultaneously detected using anodic stripping voltammetry. A standard curve is then established using standard solutions and spiked blank matrix samples to calculate the inorganic arsenic and total mercury content in the rice sample. For residual incompletely converted mercury forms or potential matrix effects, corrections or evaluations can be performed through standard reference comparison, blank matrix spike recovery, and verification using reference methods.

[0049] Sample Representativeness and Specificity: In the embodiments of this invention, the selected rice flour sample is a fixed-value sample with clearly defined mercury presence characteristics. Analysis by liquid chromatography-inductively coupled plasma mass spectrometry (LC-ICP-MS) shows that the mercury in this sample is mainly in the form of MeHg(I), exhibiting typical characteristics of samples from MeHg(I) contaminated areas. Generally, mercury contamination in Chinese rice is mainly in the coexistence of Hg(II) and MeHg(I), with MeHg(I) generally accounting for a lower proportion than in aquatic products and usually not being the primary mercury form. This invention selects a fixed-value rice flour sample with a relatively high proportion of MeHg(I) as the verification object to investigate the ability of the acidic oxidation treatment system to convert organic mercury to Hg(II). If this system can effectively convert samples with MeHg(I) as the primary mercury form, then it can also meet the requirements for unified mercury form conversion and subsequent electrochemical detection for general rice samples with a lower proportion of MeHg(I) and the coexistence of Hg(II) and MeHg(I).

[0050] Example 1: Simultaneous Detection Method of Inorganic Arsenic and Total Mercury in Rice Samples This embodiment provides a method for the simultaneous detection of inorganic arsenic and total mercury in rice samples, specifically including the following steps.

[0051] 1) Rice sample pretreatment Accurately weigh 0.2 g of rice flour sample and place it in a 10 mL centrifuge tube. The rice flour sample is a pre-determined sample, containing 0.198 mg / kg of arsenic and 0.041 mg / kg of mercury. Add 4.5 mL of acidic oxidative extraction solution to the centrifuge tube. The acidic oxidative extraction solution is a 1% potassium persulfate solution prepared with 5% hydrochloric acid (v / v). Place the sample after adding the acidic oxidative extraction solution in an ultrasonic device with a power of 200 W and sonicate at 75 °C for 10 min to ensure thorough mixing of the acidic oxidative extraction solution with the rice sample, promoting the release of bound arsenic and bound mercury from the rice matrix. During the above acidic oxidative extraction process, the extractable arsenic forms in the sample are mainly converted to As(V) after oxidation treatment; organic mercury such as MeHg(I) is converted to Hg(II) after oxidation and demethylation. Thus, total mercury mainly enters the test system in the form of Hg(II) with a strong electrochemical response, providing a basis for subsequent detection of inorganic arsenic and total mercury.

[0052] After acidic oxidation extraction, add 0.5 mL of a 2 mmol / L solution to the centrifuge tube. L- Cysteine ​​solution was used as a complexing extractant. Subsequently, the mixture was sonicated at 75 °C for 5 min to perform complexing extraction / stabilization treatment on arsenic and mercury in the system. This ensured that the arsenic and mercury released from the rice sample by oxidation existed in a more stable form after entering the extract, reducing the possibility of reverse adsorption by the rice matrix and minimizing the volatilization, adsorption, or loss of mercury during pretreatment. After complexing extraction / stabilization treatment, the sample was centrifuged at 8000 rpm for 1 min, and the supernatant was used as the extract. In the obtained extract, mercury mainly existed in the form of Hg(II), while arsenic was mainly in the form of As(V) with a small amount of As(III). The mercury speciation and extraction content in the extract could be analyzed and confirmed by LC-ICP-MS, as shown in Figure 2A(1).

[0053] 2) Composite reduction treatment Because the extract contains excess potassium persulfate, arsenic and mercury in the extract mainly exist as As(V) and Hg(II), respectively. Since the response signal of As(V) in electrochemical detection is significantly weaker than that of As(III), it is necessary to reduce As(V) to As(III) suitable for electrochemical detection. The complexation extraction / stabilization treatment described above... L Cysteine ​​can complex and stabilize arsenic and mercury in the system, but its addition is insufficient to fully reduce As(V) to As(III). Furthermore, excessive amounts... L -Cysteine ​​can mask the electrochemical signal of mercury during electrochemical detection, therefore it is not advisable to increase its concentration. L - The amount of cysteine ​​used is used to reduce As(V).

[0054] Based on this, this embodiment uses a mixed reduction system composed of sodium sulfite and hydroxylamine hydrochloride to perform a composite reduction treatment on the extract. Specifically, sodium sulfite and hydroxylamine hydrochloride are added to the extract, making the concentration of sodium sulfite 0.05 g / L and the concentration of hydroxylamine hydrochloride 0.5 g / L in the system. After mixing, a reduction reaction is carried out, and the mixture is sonicated at 75 ℃ for 5 min to obtain the test solution. After treatment with this composite reduction system, the arsenic form, mainly As(V), in the extract can be effectively reduced to As(III), while mercury mainly remains in the form of Hg(II). The changes in the speciation of arsenic and mercury after acidic oxidation extraction and composite reduction treatment are analyzed and confirmed by LC-ICP-MS, and the results are shown in Figure 2A(2).

[0055] Furthermore, the aforementioned composite reduction system does not significantly mask or interfere with the electrochemical signals of Hg(II) and As(III). When tested using subsequent electrochemical detection conditions, As(III) dissolution signals at approximately 0.1–0.2 V and Hg(II) dissolution signals at approximately 0.5–0.6 V were observed, as shown in Figure 3A. This demonstrates the feasibility of this composite reduction system in simultaneously achieving the conversion of As(V) to As(III) while maintaining the simultaneous electrochemical detection of Hg(II) and As(III).

[0056] 3) Preparation of Au@SPCE and simultaneous detection of arsenic and mercury A screen-printed carbon electrode was used as the substrate electrode. The activated screen-printed carbon electrode was placed in 1 mL of 0.1 mol / L sulfuric acid solution containing 0.1 mmol / L Au(III) for constant potential deposition. The electrodeposition solution volume was 1 mL, the deposition potential was -1.0 V, and the deposition time was 120 s. After deposition, the electrode was removed and washed with deionized water to obtain a gold nanoparticle-modified screen-printed carbon electrode, denoted as Au@SPCE.

[0057] For detection, 1 mol / L sulfuric acid was used as the electrolyte. Specifically, 0.8 mL of 1 mol / L sulfuric acid was added to 0.2 mL of the above-mentioned test solution, and the mixture was prepared as the detection solution. The prepared Au@SPCE was placed in the detection solution and enriched at a enrichment potential of -0.6 V for 300 s to enrich Hg(II) and As(III) on the Au@SPCE surface; then, linear scanning stripping voltammetry was used for detection to obtain the stripping peak currents of As(III) and Hg(II).

[0058] To achieve quantitative analysis of inorganic arsenic and total mercury in samples, a series of mixed standard solutions matching the matrix of the test solution were prepared. These mixed standard test solutions contained potassium persulfate at concentrations identical or similar to those in the sample test solution. L Cysteine, sodium sulfite, and hydroxylamine hydrochloride were used as matrix-matching components, and different concentrations of As(III) and Hg(II) standard solutions were added, respectively. The concentration ranges of As(III) and Hg(II) were 1-100 g / L. g / L. During detection, 0.2 mL of the aforementioned series of mixed standard test solutions was added to 0.8 mL of 1 mol / L sulfuric acid. The detection was performed using the same electrochemical detection procedure as the sample test solution, obtaining the dissolution peak currents of As(III) and Hg(II) respectively, and establishing standard curves. Specifically, three types of standard curves were included: the first type with a fixed As(III) concentration of 100 g / L. Hg(II) standard curves with varying Hg(II) concentrations (g / L); the second type has a fixed Hg(II) concentration of 100 g / L. The third type is the standard curve of As(III) when the concentration of As(III) changes by g / L; the standard curve of simultaneous detection when the concentrations of As(III) and Hg(II) change simultaneously.

[0059] The blank matrix spiked samples and actual rice samples underwent pretreatment, compound reduction treatment, and electrochemical detection using the same method as described above. Based on the obtained As(III) and Hg(II) dissolution peak currents and the corresponding standard curves, the concentrations of arsenic and mercury in the test solution were calculated. Furthermore, the inorganic arsenic and total mercury content in the rice samples was calculated based on the sample weight, extract volume, final test solution volume, and dilution factor during the detection process. The test results are shown in Table 3 for the fixed-value samples, including recovery rate and RSD.

[0060] Experimental Example 1: Effect of Acidic Oxidation Extraction Conditions on Mercury Speciation Conversion To investigate the effect of acidic oxidative extraction conditions on the pretreatment of rice samples, this experiment examined the effects of acid type, extraction temperature, and extraction time on the conversion of mercury speciation, focusing on the oxidative demethylation effect of MeHg(I) to Hg(II). Except for the different acidic oxidative extraction conditions, the sample weight, complexation / stabilization treatment, centrifugation conditions, and speciation analysis methods for each experimental group were the same as step 1) in Example 1. After complexation / stabilization treatment and centrifugation, the supernatant was used as the extraction solution, and the mercury speciation in the extraction solution was analyzed by LC-ICP-MS, as shown in Figure 2A. Under the preferred acidic oxidative extraction conditions, the oxidative conversion results of arsenic are shown in Figure 2B (upper part).

[0061] It should be noted that the mercury speciation analysis of the rice flour sample used in this experiment showed that its original mercury speciation was mainly MeHg(I). Therefore, Figure 2A is mainly used to evaluate the effect of different acidic oxidation extraction conditions on the conversion of MeHg(I) to Hg(II) in a sample matrix dominated by MeHg(I). The initial mercury speciation composition in rice samples from different sources or batches may vary, and the method of this invention can still promote the conversion of MeHg(I) to Hg(II) even for samples dominated by MeHg(I), thereby facilitating the normalization of the total mercury electrochemical response speciation.

[0062] Preferred group (i.e., Example 1): A 1% potassium persulfate solution prepared with 5% hydrochloric acid (v / v) was used as the acidic oxidative extraction solution, and the solution was ultrasonically treated at 75 °C for 10 min. The LC-ICP-MS analysis results are shown in Figure 2A(1). The results show that under these conditions, the mercury form in the extract was mainly converted to Hg(II), indicating that the 5% hydrochloric acid-1% potassium persulfate system combined with ultrasonic treatment at 75 °C for 10 min can effectively promote the oxidative demethylation of MeHg(I), allowing mercury to enter the test system mainly in the Hg(II) response form suitable for subsequent electrochemical detection.

[0063] Comparative Group 1: The acidic oxidative extract in Example 1 was replaced with a 1% potassium persulfate solution prepared with 5% sulfuric acid (v / v), while all other conditions remained unchanged. The rice sample was ultrasonically treated at 75 °C for 10 min to ensure thorough mixing. The LC-ICP-MS results are shown in Figure 2A(2). The relative peak area ratios of Hg(II) and MeHg(I) in the extract were 8.28% and 91.72%, respectively. The results indicate that in the 5% sulfuric acid-1% potassium persulfate system, MeHg(I) still exists in its main form, with a low degree of oxidative demethylation, which is not conducive to the total mercury entering the test system primarily in the electrochemically responsive form of Hg(II).

[0064] Comparative Group 2: The acidic oxidative extract in Example 1 was replaced with a 1% potassium persulfate solution prepared with 5% nitric acid (v / v), while all other conditions remained unchanged. The rice sample was ultrasonically treated at 75 °C for 10 min to ensure thorough mixing. The LC-ICP-MS results are shown in Figure 2A(3). The relative peak area ratios of Hg(II) and MeHg(I) in the extract were 6.53% and 93.47%, respectively. This result indicates that under the 5% nitric acid-1% potassium persulfate system, the oxidative demethylation effect of MeHg(I) is weak, and mercury mainly exists in the form of MeHg(I), which is insufficient to meet the requirements of subsequent electrochemical quantitative detection of total mercury for the response form of Hg(II).

[0065] Comparative Group 3: The acidic oxidative extraction conditions in Example 1 were changed to: using a 1% potassium persulfate solution prepared with 5% hydrochloric acid (v / v) and ultrasonic treatment at room temperature for 10 min, while keeping the other steps unchanged. The LC-ICP-MS results are shown in Figure 2A(4). The relative peak area ratios of Hg(II) and MeHg(I) in the extract were 14.79% and 85.21%, respectively. These results indicate that although MeHg(I) can undergo a certain degree of oxidative demethylation under ultrasonic treatment at room temperature for 10 min, the conversion is still insufficient. Compared with room temperature conditions, increasing the extraction temperature is beneficial to promoting the conversion of MeHg(I) to Hg(II).

[0066] As shown in Figure 2A, using a 1% potassium persulfate solution prepared with 5% hydrochloric acid and ultrasonic treatment at 75 °C for 10 min effectively promotes the release of mercury from the rice matrix and the oxidative conversion of MeHg(I) to Hg(II), allowing mercury to enter the subsequent electrochemical detection system mainly in the Hg(II) responsive form. These results indicate that this acidic oxidative extraction condition is suitable as the preferred pretreatment condition for the simultaneous detection of inorganic arsenic and total mercury in rice samples in this invention.

[0067] Experimental Example 2: Effect of Complex Extraction / Stabilizer on the Extraction Efficiency of Hg and As To investigate the effects of different complexing extractants / stabilizers on the extraction efficiency of Hg and As in rice samples, this experiment included an optimal group (Example 1), a comparative group 4, a comparative group 5, and a comparative group 6, which were respectively subjected to... L -cysteine, L Cysteine ​​hydrochloride, 2-mercaptoethanol, and 2-mercaptoacetic acid were compared as complexing extractants / stabilizers. Except for the different types of complexing extractants / stabilizers, the acidic oxidative extraction conditions, complexing extraction / stabilization treatment conditions, centrifugation conditions, and determination methods for each group were the same as in Example 1. The results are shown in Table 1.

[0068]

[0069] Specifically, the rice flour sample was subjected to acidic oxidation extraction according to the method of Example 1. The acidic oxidation extraction conditions were as follows: a 1% potassium persulfate solution prepared with 5% hydrochloric acid (v / v) was used, and the sample was ultrasonically treated at 75 °C for 10 min. After the acidic oxidation extraction was completed, a 2 mmol / L solution was added to the preferred group. L 0.5 mL of cysteine ​​solution was added to control group 4, and a concentration of 2 mmol / L of cysteine ​​solution was added to control group 4. L 0.5 mL of cysteine ​​hydrochloride solution was added to group 5, and 0.5 mL of 2 mmol / L 2-mercaptoethanol solution was added to group 6. All groups were further sonicated at 75℃ for 5 min. After complexation extraction / stabilization, the samples were centrifuged, and the supernatant was used as the extraction solution. The contents of Hg and As in the extraction solution were determined, and the relative extraction rate was calculated. The relative extraction rate is the ratio of the element content measured in the extraction solution to the sample's fixed content or the total amount measured by ICP-MS (mercury analyzer).

[0070] It should be noted that the role of the complexing extractant / stabilizer in this experimental example is mainly to ensure the stable presence of Hg and As released after acidic oxidation extraction in the extract, reducing the possibility of adsorption, re-adsorption, or loss during pretreatment. Different thiol compounds can achieve complexing extraction or stabilization of Hg and As to some extent, but their overall extraction effects on Hg and As vary. Furthermore, excessive amounts of thiol complexing agents may form strong complexes with Hg(II) or As(III), thus affecting the enrichment, deposition, or dissolution response of target ions on the electrode surface during subsequent anodic stripping voltammetry detection. Therefore, this invention uses a lower amount of complexing extractant / stabilizer to balance the stable presence of Hg and As during pretreatment with the signal response of subsequent electrochemical detection.

[0071] As shown in Table 1, the preferred group adopts... L - Cysteine ​​was used as a complexing extractant / stabilizer, and the relative extraction rates of Hg and As were 86.13% and 94.21%, respectively; Comparative group 4 used... L Using cysteine ​​hydrochloride as a complexing extractant / stabilizer, the relative extraction rates of Hg and As were 69.26% and 90.15%, respectively. In comparison group 5, 2-mercaptoethanol was used as the complexing extractant / stabilizer, with relative extraction rates of 70.53% and 74.26% for Hg and As, respectively. In comparison group 6, 2-mercaptoacetic acid was used as the complexing extractant / stabilizer, with relative extraction rates of 72.78% and 54.29% for Hg and As, respectively. These results indicate that, under the same acidic oxidative extraction conditions and complexing extraction / stabilization treatment conditions, the optimal extraction groups showed the best results. L Cysteine ​​showed a higher relative extraction rate for both Hg and As, and its overall extraction / stabilization effect was superior to that of comparison groups 1-3. L 2-Cysteine ​​hydrochloride, 2-mercaptoethanol, and 2-mercaptoacetic acid. Therefore, L - Cysteine ​​is more suitable as a preferred complexing extractant / stabilizer in the rice sample pretreatment system of this invention.

[0072] Experimental Example 3: The Influence of the Composite Reduction System on the Simultaneous Electrochemical Detection Signal of Hg and As To investigate the effects of different reduction systems on the reduction efficiency of As(V) and the simultaneous electrochemical detection signals of Hg(II) and As(III), this experimental example sets up an optimal group (i.e., Example 1) and comparative groups 7-12 for comparison. The optimal group uses a composite reduction system composed of sodium sulfite and hydroxylamine hydrochloride; comparative group 7 uses... L - Cysteine ​​was used as a reducing agent; Comparative group 8 used hydroxylamine hydrochloride as a reducing agent; Comparative group 9 used hydrazine hydrochloride as a reducing agent; Comparative group 10 used... L -Ascorbic acid was used as a reducing agent; comparative group 11 used... LThe reduction system consisted of a mixture of cysteine ​​and hydroxylamine hydrochloride; comparative group 12 used sodium sulfite as the reducing agent. Except for the different composition of the reduction system, the sample pretreatment steps, electrode types, electrochemical detection conditions, and other operations of each group were the same as in Example 1.

[0073] Specifically, following the method in Example 1, rice flour samples were sequentially subjected to acidic oxidation extraction and complexation extraction / stabilization treatment. After centrifugation, the supernatant was used as the extraction solution. Subsequently, different reduction systems were added to the extraction solution for reduction treatment, converting As(V) in the extraction solution into As(III) suitable for anodic stripping voltammetry detection. Linear anodic stripping voltammetry detection was then performed using Au@SPCE, and the results are shown in Figure 3A.

[0074] It should be noted that the role of the reduction system in this invention is not only to promote the conversion of As(V) to As(III), but also to be compatible with the simultaneous electrochemical detection system of Hg(II) and As(III). If the reducing agent or its reaction products have a strong complexing effect on Hg(II) or As(III), or cause competitive adsorption, increased background current, peak distortion, or other effects on the electrode surface, the accuracy of simultaneous detection of Hg and As may be reduced. Therefore, the reduction system suitable for this invention needs to simultaneously meet the requirements of high As(V) reduction efficiency and minimal interference with the dissolution signals of Hg(II) and As(III).

[0075] As shown in Figure 3A, when the preferred group uses a composite reduction system composed of sodium sulfite and hydroxylamine hydrochloride, both Hg and As can obtain clear dissolution response signals with good peak shapes, and the signal differentiation between the two target elements is high. This indicates that the composite reduction system can promote the reduction of As(V) while maintaining the synchronous electrochemical response of Hg(II) and As(III).

[0076] Comparison group 7 adopted L When cysteine ​​acts as a reducing agent, due to L - Cysteine ​​contains sulfhydryl and amino groups, which may form strong complexes with Hg(II) or As(III), thereby affecting the enrichment and dissolution process of target ions on the electrode surface, resulting in the suppression or interference of Hg and As detection signals.

[0077] When comparative group 8 uses hydroxylamine hydrochloride as a single reducing agent, although it has a certain reducing ability, in the detection system of this invention, the overall effect of As(V) reduction and simultaneous dissolution response of Hg and As is not as good as that of the preferred group, and the target peak response and peak shape are relatively weak.

[0078] When hydrazine hydrochloride was used as a reducing agent in Comparative Group 9, its reducing power was strong, but it was prone to causing changes in background signal or abnormal peak shape in subsequent electrochemical detection, which was not conducive to the simultaneous and stable detection of Hg and As.

[0079] Comparison group 10 adopted L - When ascorbic acid is used as a reducing agent, it can promote the reduction of As(V) to a certain extent. However, it may introduce a high background current or affect the reaction process on the electrode surface in the electrochemical system, which will affect the identification and quantitative stability of the dissolution peaks of Hg and As.

[0080] Comparison group 11 adopted L When a mixed reduction system consisting of cysteine ​​and hydroxylamine hydrochloride is used, the system still contains... L -Cysteine ​​may have a complexing effect on Hg(II) or As(III), resulting in a lower overall detection effect than the preferred group.

[0081] When sodium sulfite was used as the single reducing agent in Comparative Group 12, although sodium sulfite could participate in the reduction process of As(V), its effect on improving the simultaneous electrochemical response of Hg and As was limited when used alone, and its overall performance was not as good as the composite reduction system composed of sodium sulfite and hydroxylamine hydrochloride.

[0082] As shown in Figure 3A, different reduction systems significantly affect the reduction process of As(V) and the simultaneous electrochemical responses of Hg(II) and As(III). Compared with comparative groups 7-12, the preferred group, using a composite reduction system composed of sodium sulfite and hydroxylamine hydrochloride, can better balance the reduction efficiency of As(V) and the stability of the simultaneous electrochemical detection signals of Hg and As, without significant masking interference to the dissolution signals of the target elements. Therefore, the composite reduction system composed of sodium sulfite and hydroxylamine hydrochloride is more suitable as the preferred reduction system for detecting inorganic arsenic and total mercury in rice samples in this invention.

[0083] Experimental Example 4: Optimization of conditions for simultaneous electrochemical detection of Hg and As To further improve the sensitivity, stability, and applicability of simultaneous electrochemical detection of As(III) and Hg(II), this experimental example optimized the type of detection electrolyte and the concentration of sulfuric acid electrolyte. Except for the electrochemical detection conditions to be optimized, the remaining steps were the same as in Example 1. A mixed standard solution of As(III) and Hg(II) was used as the test system, with Au@SPCE as the working electrode. The dissolution peak currents of As(III) and Hg(II) were recorded using anodic stripping voltammetry. The peak current intensity, peak shape, background current, and peak separation effect were used as evaluation indicators. The results are shown in Figures B and C of Figure 3.

[0084] First, the effects of different detection electrolyte systems on the simultaneous dissolution signals of As(III) and Hg(II) were investigated, and the results are shown in Figure 3B. The electrochemical responses of As(III) and Hg(II) differed significantly in different electrolyte systems. The buffer salt system exhibited relatively insufficient background current and peak shape stability, with some systems showing low peak currents or poor peak separation for As(III) and Hg(II). Acidic electrolyte systems were more conducive to the reduction and enrichment of As(III) and Hg(II) on the Au@SPCE surface and subsequent anodic dissolution. Among these, the sulfuric acid system showed relatively obvious dissolution peaks for both As(III) and Hg(II), with good peak shapes and superior separation of the two target peaks; therefore, sulfuric acid was chosen as the subsequent detection electrolyte.

[0085] After determining sulfuric acid as the detection electrolyte, the effect of sulfuric acid concentration on the response signals of As(III) and Hg(II) was further investigated, and the results are shown in Figure 3C. With changes in sulfuric acid concentration, the dissolution peak currents of As(III) and Hg(II) changed significantly. At lower sulfuric acid concentrations, As(III) achieved a higher response, but the response of Hg(II) was relatively weak, which was not conducive to the simultaneous and sensitive detection of the two elements. As the sulfuric acid concentration increased, the peak current of Hg(II) gradually increased, while As(III) maintained a relatively high detectable response. When the sulfuric acid concentration further increased, the responses of both As(III) and Hg(II) decreased, indicating that excessively high acidity may affect the enrichment or dissolution process of target ions on the electrode surface. Considering the response intensity, peak shape, background current, and applicability of simultaneous detection for As(III) and Hg(II), a sulfuric acid concentration of 1.0 mol / L was selected.

[0086] Example 2: Verification of non-interference between blank rice matrix spiked calibration and simultaneous arsenic and mercury detection To verify the quantitative applicability of the method of the present invention in rice sample matrix and to investigate the mutual influence of As(III) and Hg(II) during simultaneous detection, a calibration relationship between As(III) and Hg(II) was established by spiking a blank rice matrix. Except for the spiking method, the sample pretreatment, electrode preparation, and electrochemical detection conditions were all the same as those in Example 1. The detection results are shown in Figure 4 and Table 2.

[0087]

[0088] Blank rice samples that were not detected or whose target analyte content was negligible were selected and subjected to acidic oxidation extraction, complexation extraction / stabilization treatment, and reduction treatment according to the method described in Example 1 to obtain a blank rice matrix extract. Subsequently, As(III) and Hg(II) standard solutions of different concentrations were added to the blank rice matrix extract to prepare a spiked blank rice matrix sample, and anodic stripping voltammetry was performed using Au@SPCE to record the stripping peak currents of As(III) and Hg(II).

[0089] This embodiment sets three matrix spiking methods: First, the As(III) concentration is fixed at 100%. Under the condition of g / L, the Hg(II) concentration is kept between 1-300 g / L. The concentration was increased gradually within the range of g / L (denoted as Hg(II)-1), and the results are shown in Figure 4A; secondly, the Hg(II) concentration was fixed at 100 g / L. Under the condition of g / L, the As(III) concentration is kept between 1-300 g / L. The concentrations were increased gradually within the range of g / L (denoted as As(III)-1), and the results are shown in Figure 4B; third, the concentrations of As(III) and Hg(II) were kept within the range of 1-300 g / L. Simultaneous increases within the g / L range (denoted as As(III)-2 and Hg(II)-2), the results are shown in Figure 4C. Using the above three methods, the effects of As(III) coexistence on Hg(II) detection, the effects of Hg(II) coexistence on As(III) detection, and the linear response when both change synchronously were investigated.

[0090] As shown in Figure 4A, under the condition of fixed As(III) concentration and increasing Hg(II) concentration, i.e. the first spiking method, the Hg(II) dissolution peak current gradually increases with increasing concentration and shows a good concentration dependence. At the same time, the position and peak current of As(III) dissolution peak change little, indicating that in the detection system of the present invention, the coexistence of fixed concentration of As(III) has no significant interference with the electrochemical detection of Hg(II).

[0091] As shown in Figure 4B, under the condition of fixed Hg(II) concentration and increasing As(III) concentration, i.e. the second spiking method, the As(III) dissolution peak current gradually increases with its concentration and shows a good concentration dependence; at the same time, the Hg(II) dissolution peak changes little, indicating that the coexistence of fixed concentration of Hg(II) has no significant interference with the electrochemical detection of As(III).

[0092] As shown in Figure 4C, under the condition of simultaneous increase of As(III) and Hg(II) concentrations, i.e. the third spiking method, both As(III) and Hg(II) show clear and distinguishable dissolution peaks. The peak currents of both increase with increasing concentration, indicating that the method of the present invention can achieve simultaneous electrochemical detection of As(III) and Hg(II) in rice matrix, and the two target substances do not produce obvious mutual masking or peak overlap interference within the concentration range.

[0093] As shown in Table 2, under the conditions of spiked blank rice matrix, As(III) and Hg(II) exhibited piecewise linear response characteristics in the range of 1-300 mg / L. Specifically, the response range of 1-100 mg / L was [not specified in the original text]. The low concentration range (g / L) exhibits a high slope and good linearity, making it suitable for sensitive detection of trace As and Hg in rice samples; 100-300 g / L The high g / L concentration range maintains a good linear relationship, making it suitable for quantitative analysis of samples at higher concentration levels. The correlation coefficients of the linear regression equations for each segment are all greater than 0.99, indicating that segmented calibration can more accurately reflect the enrichment and dissolution response of As(III) and Hg(II) on the Au@SPCE surface, improving the reliability of quantification at different concentration levels.

[0094] Table 2 also shows that the method of the present invention has low limits of detection and quantitation, and good repeatability. When the concentration of one target analyte changes, the response signal of the other target analyte remains essentially stable; even when both are increased simultaneously, good peak separation and piecewise linear response are still maintained. Therefore, a piecewise calibration relationship established by spiking a blank rice matrix can be used for simultaneous quantitative analysis of As and Hg in actual rice samples.

[0095] Example 3: Detection of fixed-value rice samples and verification of spiked recovery of mixed speciation in blank matrix To verify the accuracy and practical applicability of the method of the present invention for the simultaneous detection of arsenic and mercury in rice samples, spiked samples in the mixed form of blank rice matrix extract and fixed-value rice samples were used for determination, and the results are shown in Table 3.

[0096] Blank rice samples were taken, and blank rice matrix extracts were prepared according to the method described in Example 1. Different concentrations of arsenic and mercury standard solutions were added to obtain three spiking levels of blank matrix spiked samples: low, medium, and high. The mercury spikes included MeHg(I) and Hg(II), and the arsenic spike was As(III). After acidic oxidation extraction, oxidative demethylation, complexation extraction / stabilization, and composite reduction treatment, the spiked samples were subjected to anodic stripping voltammetry detection using Au@SPCE under the preferred electrochemical detection conditions determined in Example 5. Based on the segmented calibration relationship of the blank rice matrix spikes established in Example 2, the detection values ​​of Hg and As were calculated. The recovery rate and relative standard deviation were calculated after subtracting the blank value from the theoretical spiking amount.

[0097] Simultaneously, a fixed-value rice flour sample was taken and analyzed using the same pretreatment and detection steps as the above-mentioned sample. The obtained detection values ​​were compared with the fixed-value results of the sample to evaluate the accuracy of the method of the present invention for the simultaneous detection of arsenic and mercury in real rice samples. The values ​​in parentheses in Table 3 are the concentration results obtained by ICP-MS and mercury analyzer after sample dilution.

[0098]

[0099] Table 3 shows that in the mixed-form spiking system of blank rice matrix extract, the method of the present invention has good recovery effects for both Hg and As. Specifically, at the low, medium, and high spiking levels, the recoveries of Hg were 90.37%, 86.83%, and 86.04%, respectively, and the recoveries of As were 93.02%, 95.27%, and 94.28%, respectively. The relative standard deviations were all within acceptable ranges, indicating that the method of the present invention has good detection accuracy and repeatability for arsenic and mercury under rice matrix conditions.

[0100] For the rice flour sample with a fixed value, the Hg and As contents measured by the method of this invention were 33.86 mg / L and 183.21 mg / L, respectively, which are basically consistent with the fixed value results of 41.11 mg / L and 198.23 mg / L, with detection rates of 81.26% and 90.87%, respectively. This indicates that the method of this invention can be applied to the simultaneous detection of arsenic and mercury in real rice samples. Combining the results of the blank matrix mixed speciation spiked and the results of the fixed value sample determination, it can be seen that the method of this invention can achieve simultaneous pretreatment, simultaneous electrochemical detection and quantitative analysis of Hg and As in the complex matrix of rice samples, and has good practical application applicability.

[0101] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All embodiments falling under the scope of the present invention... Obvious variations or modifications derived from the technical solution are still within the scope of protection of this invention.

Claims

1. A method for pretreatment conversion and simultaneous electrochemical detection of inorganic arsenic and total mercury in rice, characterized in that, Includes the following steps: S1. Add acidic oxidative extract to the rice flour to be tested, heat and sonicate to fully release arsenic and mercury from the rice matrix and convert some of the arsenic and mercury into As(V) and Hg(II), centrifuge to obtain the extract; S2. Add a composite reducing agent to the extract to further reduce As(V) in the extract to As(III) to obtain the test solution; S3. The contents of As(III) and Hg(II) in the test solution are tested by electrochemical methods to determine the contents of inorganic arsenic and total mercury in the rice to be tested; The acidic oxidative extract includes inorganic acids and persulfate oxidants, and the composite reducing agent includes sulfites and / or hydroxylamine salts.

2. The detection method according to claim 1, characterized in that, The inorganic acid is hydrochloric acid, and the persulfate oxidant is potassium persulfate and / or ammonium persulfate; Preferably, the volume fraction of the inorganic acid is 1-10%; Preferably, the mass fraction of the persulfate oxidant is 0.5-4%; Preferably, the mass-to-volume ratio of the rice flour to be tested to the acidic oxidative extract is 1 g / 5 mL to 0.2 g / 5 mL.

3. The detection method according to claim 1, characterized in that, The sulfite is sodium sulfite, and the hydroxylamine salt is hydroxylamine hydrochloride; Preferably, the composite reducing agent is sodium sulfite and hydroxylamine hydrochloride; Preferably, the concentration of sulfite in the extract is 0.01-0.2 g / L; Preferably, the concentration of the hydroxylamine salt in the extract is 0.1-1.0 g / L.

4. The detection method according to claim 1, characterized in that, In step S1, the ultrasonic temperature is 50-85 ℃ and the ultrasonic time is 3-15 min.

5. The detection method according to claim 1, characterized in that, Before centrifugation in step S1, a complexing extractant is further added to the system to achieve complexation stabilization of arsenic and mercury in the system. Preferably, the complexing extractant is selected from... L -cysteine, L One or more of cysteine ​​hydrochloride, mercaptoacetic acid, and mercaptoethanol; Preferably, the concentration of the complexing extractant in the system is 0.5-5 mM.

6. The detection method according to claim 1, characterized in that, Step S3 further includes: The test solution and electrolyte were mixed, and a nano-gold modified screen-printed carbon electrode was used as the working electrode. The anodic stripping voltammetry was used for detection. The content of inorganic arsenic and total mercury in the rice to be tested was calculated based on the stripping peak current values ​​of As(III) and Hg(II).

7. The detection method according to claim 6, characterized in that, The nano-gold modified screen-printed carbon electrode was prepared according to the following steps: The screen-printed carbon electrode is placed in a nano-gold deposition solution containing a gold precursor. After electrodeposition, a nano-gold modification layer is formed on the surface of the screen-printed carbon electrode, thus obtaining the desired product. The gold-containing precursor includes chloroauric acid, chloroaurate or their hydrates, preferably trichloroauric acid hydrate or tetrachloroauric acid hydrate; The supporting electrolyte in the nano-gold deposition solution is an acidic supporting electrolyte, preferably sulfuric acid, hydrochloric acid, or nitric acid.

8. The detection method according to claim 7, characterized in that, The concentration of the gold precursor in the nano-gold deposition solution is 0.05-1 mM; The concentration of the supporting electrolyte in the gold nanoparticle deposition solution is 0.5-1.25 M.

9. The detection method according to claim 6, characterized in that, The electrodeposition includes constant potential deposition, constant current deposition, or cyclic voltammetric deposition; Preferably, the deposition potential of the constant potential deposition is -0.6 to -1.1 V.

10. The detection method according to claim 6, characterized in that, The volume ratio of the test liquid to the electrolyte is 100-400:600-900.

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