Preparation method and application of electrode capable of simultaneously detecting amaranth, carmine and indigo

Abstract

The application relates to the field of electrochemical analysis methods, and particularly discloses a preparation method of an electrode capable of simultaneously detecting amaranth, carmine and indigo and application of the electrode; the electrode preparation method is as follows: firstly, Fe / Co Prussian blue seed modified carbon fiber paper is prepared through a chemical deposition method; secondly, the Fe / Co Prussian blue seed modified carbon fiber paper is subjected to a hydrothermal reaction to prepare hollow cubic octahedral Fe / Co Prussian blue nanomaterial modified carbon fiber paper electrode; finally, the hollow cubic octahedral Fe / Co oxide nanomaterial modified carbon fiber paper electrode (CoFe2O4@CFP) is obtained through calcination. The CoFe2O4@CFP electrode is used as a working electrode, and the content of the three pigments, i.e. amaranth, carmine and indigo, in a sample to be detected can be simultaneously detected by adopting a differential pulse voltammetry method combined with a chronoamperometry method. Compared with other methods, the method has the advantages of simple preparation, rapid detection, wide application in simultaneous determination of amaranth, carmine and indigo in actual samples such as candies, tap water and beverages, high detection sensitivity, wide detection range and great practical application potential.

Description

Technical Field

[0001] This invention relates to an electrochemical sensor and its applications, particularly to the preparation and application methods of an electrode for the simultaneous detection of three pigments: indigo (IC), carmine (Pon), and amaranth (Amar). This electrode can be widely used in the simultaneous quantitative analysis of IC, Pon, and Amar pigments in the food, pharmaceutical, and environmental fields. Technical Background

[0002] Pigments are important additives in many fields such as food, cosmetics, and textiles. They are particularly widely used as colorants in food and pharmaceuticals, with natural or synthetic pigments such as indigo, carmine, and amaranth being widely applied. However, with the excessive use of these pigments, their potential health hazards have gradually attracted attention. Studies have shown that consuming large amounts of food or beverages containing certain artificial pigments (such as indigo, carmine, and amaranth) may lead to abnormal liver function and kidney damage. Furthermore, the accumulation of these pigments may damage genes and increase the risk of cancer. In particular, some synthetic pigments may have negative effects on children's neurobehavior, increasing the risk of problems such as attention deficit hyperactivity disorder (ADHD). Therefore, efficient, accurate, and selective detection of these pigments to ensure their safe use has become a crucial task.

[0003] Traditional pigment detection methods, such as spectrophotometry, high-performance liquid chromatography-mass spectrometry, fluorescence emission spectroscopy, and capillary electrophoresis, while possessing high sensitivity and providing relatively accurate analytical results, typically require complex operating procedures, incur high costs, and have long detection times. Furthermore, traditional methods often struggle to simultaneously detect multiple pigments, especially in complex sample systems where they are easily interfered with by other components, thus affecting the accuracy and efficiency of detection. To address these issues, electrochemical sensors, due to their ease of operation, low cost, fast response, and portable monitoring capabilities, have gradually become a powerful tool in pigment detection. However, existing electrochemical sensors face several key challenges: (1) Selectivity: Different pigments exhibit similar electrochemical behaviors, making it difficult for existing sensors to selectively detect specific pigments, especially in complex samples where this interference problem is particularly pronounced. (2) Sensitivity: While existing electrochemical methods can detect pigments, their sensitivity and detection range are often insufficient, particularly at low concentrations, making it difficult to accurately detect pigments such as indigo, carmine, and amaranth. (3) Stability issues: Existing electrode materials may face stability issues during long-term use, which may affect the repeatability and long-term detection performance of the electrode.

[0004] Therefore, improving the selectivity, sensitivity, and stability of electrochemical sensors by optimizing electrode materials and refining sensing mechanisms has become a key research topic. Developing novel electrode materials or modification techniques can effectively address these technical bottlenecks, enabling efficient and selective detection of indigo, carmine, and amaranth, which has significant application value. Summary of the Invention

[0005] This invention provides a method for preparing and applying an electrode capable of simultaneously detecting three pigments: indigo (IC), carmine (Pon), and amaranth (Amar). This electrode, prepared using an in-situ growth method, exhibits excellent selectivity, sensitivity, and stability. It enables accurate and rapid simultaneous detection of these three pigments in complex samples and can be widely applied to pigment detection in food, pharmaceuticals, and environmental fields. To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0006] 1. Preparation of an electrode capable of simultaneously detecting three pigments: indigo (IC), carmine (Pon), and amaranth (Amar). The electrode preparation method provided by this invention includes the following steps:

[0007] Step (1): After preheating the carbon fiber paper (CFP) in an oven at 200℃ for 20 minutes, it is then successively immersed in a mixed aqueous solution containing cobalt salt and sodium citrate, and then in an aqueous solution containing potassium ferricyanide. Each immersion time is 20 seconds. After immersion, the carbon fiber paper is placed in an oven and pyrolyzed at 200℃ for 5-10 minutes. This process is repeated twice to obtain Fe / Co-based Prussian blue seed-modified carbon fiber paper.

[0008] Step (2): Add the mixed aqueous solution containing cobalt salt and sodium citrate to the potassium ferricyanide aqueous solution, stir evenly, and pour into a high-pressure reactor lined with polytetrafluoroethylene. Place the Fe / Co-based Prussian blue seed-modified carbon fiber paper obtained in step (1) into the reactor, control the temperature at 50-150℃, and carry out a hydrothermal reaction for 2-8 hours. After the reaction is completed, cool to room temperature, remove the carbon fiber paper, rinse with deionized water and dry to obtain a hollow cubic octahedral Fe / Co-based Prussian blue nanomaterial-modified carbon fiber paper electrode.

[0009] Step (3): Place the above electrode in a tube furnace and calcine it in an air atmosphere at 100-350°C for 1-3 hours. After removing it, cool it to room temperature, rinse it with deionized water and dry it to obtain carbon fiber paper (CoFe2O4@CFP) modified with hollow cubic octahedral Fe / Co oxide nanomaterials. Cut it into a rectangle of 1 cm × 2 cm to obtain an electrode that can simultaneously detect three pigments: amaranth, carmine and indigo.

[0010] Furthermore, according to the electrode preparation method of the present invention, the cobalt salt in steps (1) and (2) can be selected from cobalt acetate, cobalt chloride, and cobalt nitrate.

[0011] Furthermore, the molar concentration of the cobalt salt aqueous solution is 0.01–0.1 mol / L, and the molar ratio of cobalt salt to sodium citrate is 1:1.5. Furthermore, the molar concentration of the potassium ferricyanide aqueous solution is 0.01–0.05 mol / L.

[0012] 2. An application method for an electrode capable of simultaneously detecting three pigments: indigo (IC), carmine (Pon), and amaranth (Amar).

[0013] This invention provides a method for the simultaneous detection of target pigments using a combination of differential pulse voltammetry (DPV) and chronoamperometry (CA), based on the aforementioned CoFe2O4@CFP electrode as the working electrode, a saturated calomel electrode as the reference electrode, a platinum wire electrode as the counter electrode, and 0.1M phosphate buffer solution (PBS, pH 7.0) as the electrolyte. The specific steps include:

[0014] Standard solution detection:

[0015] (1) Add a standard solution containing IC, Pon and Amar to the electrolyte, scan the test solution using DPV, and record the current response at different potentials;

[0016] (2) The CoFe2O4@CFP electrode can identify and oxidize three pigments at different potentials, indigo is oxidized at lower potentials, carmine is oxidized at medium and high potentials, and amaranth is oxidized at high potentials.

[0017] (3) The chronoamperometry curves of the three pigment standard solutions at the above low, medium and high potentials were measured respectively, and a standard curve between pigment concentration and current response was established.

[0018] Unknown sample detection:

[0019] (1) Add the sample to be tested to the electrolyte and perform current response detection at the lowest potential. If a response is generated, calculate the concentration of indigo in the solution based on the standard curve between pigment concentration and current response at low potential. If there is no response, continue to increase the potential for detection.

[0020] (2) Current response detection is performed at medium to high potential. If a response is generated, the concentration of carmine in the solution is calculated based on the standard curve between pigment concentration and current response at medium to high potential, while the effect of the measured concentration of indigo on the current is subtracted. If there is no response, the potential is increased further for detection.

[0021] (3) At the highest potential, the current response is detected. If a response is generated, the concentration of amaranth in the solution is calculated based on the standard curve between the pigment concentration and the current response at the high potential, while deducting the influence of the measured concentrations of indigo and carmine on the current. If there is no response, it is determined that the sample does not contain the target pigment.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] (1) The present invention uses simple soaking pyrolysis, hydrothermal reaction, calcination and other methods to directly modify Fe-Co Prussian blue nano-oxides onto carbon fiber paper in situ, so as to obtain carbon fiber paper electrodes that do not require additional adhesives. These electrodes have good conductivity, structural stability and designability, simplify the preparation process and reduce costs.

[0024] (2) The electrode material obtained by this invention can accurately quantify indigo, carmine, and amaranth at different potentials, with high detection sensitivity and short response time, making it suitable for real-time monitoring of complex samples. By comparing standard curves, the simultaneous detection of the three pigments can be effectively performed, providing reliable technical support for pigment detection in the fields of food, pharmaceuticals, and environment.

[0025] (3) The electrode prepared by the present invention has good stability, can be used for a long time in practical applications, and can be repeatedly tested, showing high practicality and application potential. Attached Figure Description

[0026] Figure 1 The image shows scanning electron microscope (SEM) and transmission electron microscope (TEM) images of CoFe2O4@CFP.

[0027] Figure 2 The X-ray diffraction (XRD) patterns of CoFe2O4@CFP and CoFe2O4 are shown.

[0028] Figure 3 Differential pulse voltammetry (DPV) curves of standard solutions of indigo (IC), carmine (Pon), and amaranth (Amar) and their mixtures on a CoFe2O4@CFP electrode are shown.

[0029] Figure 4 Linear relationships between pigment concentration and current response for standard solutions of indigo (IC), carmine (Pon), and amaranth (Amar) at low, medium, and high potentials are shown. Detailed Implementation

[0030] The invention will be further described below with reference to the accompanying drawings:

[0031] Implementation Case 1

[0032] 1. A method for preparing an electrode capable of simultaneously detecting three pigments: indigo, carmine, and amaranth, comprising the following steps: Step (1): After preheating carbon fiber paper (CFP) in an oven at 200°C for 20 minutes, it is sequentially immersed in a mixed aqueous solution containing 0.03M Co(NO3)2 and 0.045M sodium citrate, and then in an aqueous solution containing 0.02M potassium ferricyanide, with each immersion lasting 20 seconds. After immersion, it is placed in an oven and subjected to a pyrolysis reaction at 200°C for 5 minutes. This process is repeated twice to obtain carbon fiber paper modified with Fe / Co-type Prussian blue seeds.

[0033] Step (2) Mix the mixed aqueous solution containing 0.03M Co(NO3)2 and 0.045M sodium citrate with 0.02M potassium ferricyanide aqueous solution and pour it into a hydrothermal reactor. Place the carbon fiber paper modified with Fe / Co-type Prussian blue seed crystals obtained in step (1) into the reactor and hydrothermally heat at 100℃ for 6 hours. After the reaction is completed, cool to room temperature, take out the carbon fiber paper, rinse with deionized water, and dry to obtain a hollow cubic octahedral Fe / Co-type Prussian blue nanomaterial modified carbon fiber paper electrode.

[0034] Step (3) Place the above electrode in a tube furnace and calcine it in an air atmosphere at 250°C for 2 hours. After taking it out, cool it to room temperature, rinse it with deionized water, and dry it to obtain a carbon fiber paper electrode modified with hollow cubic octahedral Fe / Co oxide nanomaterials, denoted as CoFe2O4@CFP. Cut it into a rectangle of 1 cm × 2 cm to obtain a CoFe2O4@CFP electrode that can simultaneously detect three pigments: amaranth, carmine, and indigo.

[0035] The inventors examined the CoFe2O4@CFP electrode obtained in the above process using scanning electron microscopy and transmission electron microscopy, and the results are as follows: Figure 1 As shown. Figure 1 The morphology of CoFe2O4@CFP is depicted, showing uniformly grown nano-hollow CoFe2O4 cubic octahedral particles on the carbon fiber surface. This was achieved using a magnified scanning electron microscope. Figure 1 b and c show that the size of the CoFe2O4 cubic octahedral particles is approximately 200 nm. The EDS of CoFe2O4@CFP is shown below. Figure 2 As shown, Co, Fe, O, and C elements are uniformly distributed on the electrode surface. TEM images of CoFe₂O₄ nanoparticles at different magnifications are shown below. Figure 1 As shown in image e, CoFe₂O₄ is a hollow cubic octahedron, composed of numerous nanoparticles, each approximately 10 nm in size. Further magnification is seen in the high-resolution TEM image (…). Figure 1f) Clear lattice fringes were observed. The spacing of the lattice fringes was 0.295 nm and 0.253 nm, corresponding to the 220 and 311 planes of the cobalt ferrite (CoFe2O4) phase. These lattice spacings are consistent with the characteristic crystal planes of the cubic phase of CoFe2O4, confirming the presence of this specific phase in the sample.

[0036] Depend on Figure 2 The XRD pattern shows that the prepared CoFe2O4@CFP electrode exhibits standard CoFe2O4 characteristic diffraction peaks.

[0037] Implementation Case 2

[0038] The inventors, using a combination of differential pulse voltammetry and chronovoltammetry, simultaneously detected the contents of indigo (IC), carmine (Pon), and amaranth (Amar) on the CoFe2O4@CFP electrode prepared in Implementation Case 1, evaluating the electrochemical response capability of the CoFe2O4@CFP electrode. The prepared CoFe2O4@CFP electrode was used as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire electrode as the counter electrode. Standard solutions containing indigo, carmine, and amaranth were added to a pH 7.0 PBS buffer solution, and differential pulse voltammetry was performed. The results showed that within the potential range of 0.1V to 0.9V, the CoFe2O4@CFP electrode recognized and oxidized the three pigments at different potentials. Indigo was oxidized at a low potential of 0.35V, carmine at a medium-high potential of 0.56V, and amaranth at a high potential of 0.69V. Figure 3 As shown.

[0039] Chronoamperometry curves of the three pigment standard solutions were measured at the three potentials (low (0.35V), medium-high (0.56V), and high (0.69V) respectively. Standard curves were then established to correlate pigment concentration with current response. Figure 3 As shown in the table below, the specific linear equations are as follows.

[0040] Table 1. Linear equations relating the concentrations of indigo, carmine, and amaranth at different potentials to the current response.

[0041]

[0042] (C IC Indigo concentration, I IC For indigo current response; C Pon I represents the concentration of carmine. Pon For carmine current response; C Amar For amaranth red concentration, I Amar (For the red current response of amaranth)

[0043] Implementation Case 3: Simultaneous Determination of Amaranth, Carmine, and Indigo in Rainbow Candy Pigment Extract

[0044] Ten Ludi Rabbit Skittles (97166301#) were weighed and added to 20 mL of ethanol-water (1:1, v / v) mixture. The mixture was magnetically stirred for 10 min. The extract was centrifuged at 10000 rpm for 5 min to remove insoluble impurities. The filtrate was filtered through a 0.45 μm filter membrane to obtain a clear pigment solution. The supernatant was diluted with phosphate buffer solution to the detection concentration. The CoFe2O4@CFP electrode prepared in Example 1 was used as the working electrode. The contents of IC, Pon, and Amar in the actual Skittles sample were detected by the spiked recovery method. It was found that the electrode had a good recovery rate, reaching 99.0%–106.7%.

[0045] Table 1. Simultaneous determination of IC, Pon, and Amar content in Skittle candy samples using the spiking recovery method.

[0046]

[0047]

[0048] a. Five parallel measurements were performed.

[0049] Implementation Case 4: Simultaneous Determination of Amaranth, Carmine, and Indigo in Tap Water

[0050] Tap water from Haizhou District, Lianyungang City, Jiangsu Province was diluted with phosphate buffer solution to the detection concentration. Using the CoFe2O4@CFP electrode prepared in Example 1 as the working electrode, the contents of IC, Pon, and Amar in the actual tap water were detected by the spiked recovery method. It was found that the electrode had a good recovery rate, reaching 96.7%–106.0%.

[0051] Table 2. Simultaneous determination of IC, Pon, and Amar content in tap water samples using the spiking recovery method.

[0052]

[0053] a. Five parallel measurements were performed.

[0054] The present invention has been disclosed above with reference to preferred embodiments only, but is not intended to limit the invention in any other way. Any modifications, equivalent substitutions, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the claims.

Claims

1. A method for preparing an electrode capable of simultaneously detecting indigo, carmine and amaranth, characterized in that, The preparation method comprises the following processes: Step (1): after the carbon fiber paper CFP is preheated in an oven at 200 DEG C for 20 minutes, it is sequentially immersed in a mixed aqueous solution containing a cobalt salt and sodium citrate, and a potassium ferricyanide aqueous solution, each time for 20 seconds, and then taken out and placed in the oven for pyrolysis reaction at 200 DEG C for 5-10 minutes; the process is repeated twice to obtain the carbon fiber paper modified by Fe / Co Prussian blue seeds; Step (2): the mixed aqueous solution containing the cobalt salt and sodium citrate is added to the potassium ferricyanide aqueous solution, stirred uniformly, and then poured into a polytetrafluoroethylene-lined autoclave, and the carbon fiber paper modified by the Fe / Co Prussian blue seeds obtained in step (1) is placed in the autoclave for hydrothermal reaction at 50-150 DEG C for 2-8 hours; after the reaction is completed, the autoclave is cooled to room temperature, and the carbon fiber paper is taken out, washed with deionized water, and dried to obtain the carbon fiber paper electrode modified by hollow cubic octahedral Fe / Co Prussian blue nanomaterials; Step (3): the electrode is placed in a tube furnace and calcined in an air atmosphere at 100-350 DEG C for 1-3 hours, and then taken out and cooled to room temperature, washed with deionized water, and dried to obtain the carbon fiber paper electrode modified by hollow cubic octahedral Fe / Co oxide nanomaterials, which is denoted as CoFe2O4@CFP, and cut into a 1 cm x 2 cm rectangle to obtain an electrode capable of simultaneously detecting amaranth, carmine and indigo.

2. The preparation method of the electrode capable of simultaneously detecting indigo, carmine and amaranth according to claim 1, characterized in that, The cobalt salt in steps (1) and (2) is one of cobalt acetate, cobalt chloride and cobalt nitrate.

3. The preparation method of the electrode capable of simultaneously detecting indigo, carmine and amaranth according to claim 1, characterized in that, The molar concentration of the cobalt salt aqueous solution in steps (1) and (2) is 0.01-0.1 mol / L, and the molar ratio of the cobalt salt to sodium citrate is 1:1.

5.

4. The preparation method of the electrode capable of simultaneously detecting indigo, carmine and amaranth according to claim 1, characterized in that, The molar concentration of the potassium ferricyanide aqueous solution in step (1) is 0.01-0.05 mol / L.

5. A method for simultaneously detecting indigo, carmine and amaranth electrodes, characterized in that, The CoFe2O4@CFP electrode of any one of claims 1-4 is used as a working electrode, a saturated calomel electrode is used as a reference electrode, a platinum wire electrode is used as a counter electrode, a phosphate buffer solution PBS, pH 7.0 is used as an electrolyte, and the contents of amaranth, carmine and indigo in a sample are simultaneously detected by differential pulse voltammetry DPV combined with chronoamperometry CA, which specifically comprises the following steps: (1) a standard solution containing amaranth, carmine and indigo is added to the electrolyte, the to-be-detected solution is scanned by DPV, and the current response at different potentials is recorded; the CoFe2O4@CFP electrode recognizes and oxidizes the three pigments at different potentials, wherein indigo is oxidized at a low potential, carmine is oxidized at a medium-high potential, and amaranth is oxidized at a high potential; (2) the chronoamperometry curves of the three pigment standard solutions at the above low, medium-high and high potentials are respectively determined, and a standard curve between the corresponding pigment concentration and the current response is established.

6. Use according to claim 5, characterized in that, The recognition and quantitative analysis of the three pigments are realized by CA step-by-step potential scanning, which specifically comprises the following steps: (1) adding the sample to be tested into the electrolyte, detecting the current response at the low potential, if the current response is detected, calculating the concentration of indigo in the solution based on the standard curve between the concentration of the pigment and the current response at the low potential; if the response is not detected, continuously increasing the detection potential; (2) detecting the current response at the medium-high potential, if the current response is detected, calculating the concentration of carmine in the solution based on the standard curve between the concentration of the pigment and the current response at the medium-high potential, and deducting the influence of the measured concentration of indigo on the current signal; if the response is not detected, continuously increasing the detection potential; (3) detecting the current response at the high potential, if the current response is detected, calculating the concentration of amaranth in the solution based on the standard curve between the concentration of the pigment and the current response at the high potential, and deducting the influence of the measured concentrations of indigo and carmine on the current signal; if the response is not detected, determining that the sample does not contain the target pigment.

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