Digestion method and detection method for ICP-MS (Inductively Coupled Plasma Mass Spectrometry) detection of cationic guar gum

Abstract

The invention relates to the field of chemical analysis, in particular to a digestion method and a detection method for ICP-MS (Inductively Coupled Plasma Mass Spectrometry) detection of cationic guar gum. The invention relates to a digestion method for cationic guar gum ICP-MS detection. The digestion method comprises the following steps: S1, accurately weighing a sample; s2, pre-digestion: enabling the sample to be in full contact with concentrated nitric acid; s3, adding hydrogen peroxide; s4, carrying out digestion in a high-pressure tank; and S5, post-processing: fixing the volume for later use. The ICP-MS determination method using the digestion method comprises the following steps: A1, preparing a standard curve and an internal standard solution; a2, ICP-MS instrument condition determination: using helium as collision gas; and A4, calculating a result. According to the method, a nitric acid-hydrogen peroxide and high-pressure tank assisted digestion technology is adopted to thoroughly decompose organic macromolecules, and then the digested solution is detected by using an ICP-MS method, so that the characteristic elements in the cationic guar gum can be accurately and sensitively measured.

Description

Technical Field

[0001] This invention relates to the field of chemical analysis, specifically a digestion method and detection method for cationic guar gum by ICP-MS. Background Technology

[0002] Cationic guar gum, a modified product of the natural polymer guar gum, has been widely adopted in many important sectors of the national economy, including food, cosmetics, oil extraction, papermaking, and textiles, due to its excellent water solubility, thickening properties, suspension stability, and cationic surface activity. Its unique molecular structure allows it to function as both a thickener and emulsifier in systems, and to achieve adsorption and fixation through the interaction of cationic groups with the negative charge on the matrix surface, making it a key functional ingredient in many product formulations. However, there is a possibility of introducing metal elements throughout the entire chain of cationic guar gum production, from raw material acquisition and modification processing to storage and transportation. The content of these metal elements directly affects product quality, safety, and industry compliance. Therefore, establishing scientific detection methods and clarifying the levels of metal element content is of significant practical importance and industry value.

[0003] The determination of heavy metal elements mainly employs techniques such as atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectrometry (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), atomic fluorescence spectrometry (AFS), and electrochemical analysis. Atomic absorption spectrometry (AAS) is the most commonly used method for heavy metal detection, offering good reproducibility and strong anti-interference capabilities. However, it can only determine one element per test, resulting in low detection efficiency. It also exhibits low atomization efficiency for high-melting-point metals and is susceptible to matrix interference. Atomic fluorescence spectrometry (AFS) determines heavy metal content by measuring the fluorescence emission intensity of atomic vapors under specific frequency radiation. It boasts higher sensitivity than AAS and a wider linear range, but its sensitivity is low for non-hydride-generating elements such as sodium, calcium, and iron, limiting its applicability. It is also susceptible to matrix interference and environmental factors such as temperature and humidity, requiring strict control of reaction conditions. Inductively coupled plasma atomic emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) offer extremely low detection limits and high selectivity, enabling the simultaneous detection of multiple heavy metal elements and isotopes, making them particularly suitable for trace analysis in environmental and food fields. Each method has its advantages and disadvantages; the appropriate technique should be selected based on the specific detection requirements, sample type, and accuracy requirements.

[0004] Digestion is a crucial pretreatment step for the detection of metal elements in cationic guar gum. Its purpose is to break down the organic matrix in the sample, allowing the metal elements to be completely released and converted into a soluble state, while simultaneously eliminating matrix interference and creating a homogeneous and stable analytical system for subsequent determinations. Because cationic guar gum contains a large amount of carbon, hydrogen, and oxygen elements, and may exhibit coordination interactions with metal ions, a suitable digestion method must be selected based on the detection requirements, the type of metal element, and the characteristics of the instrument.

[0005] When analysts attempted to apply advanced ICP-MS to the detection of cationic guar gum, they encountered significant challenges due to the inherent characteristics of the sample, primarily in the sample digestion process. Cationic guar gum is a high-molecular-weight polysaccharide that readily dissolves in water at room temperature to form a high-viscosity solution, but it is prone to clumping or carbonization in strong acids. Traditional hotplate digestion using a nitric acid-sulfuric acid system is highly susceptible to localized overheating, which can cause the sample to carbonize into black charred lumps, trapping the analyte and preventing complete release. This results in significantly lower values, impacting data accuracy and precision. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a digestion method and detection method for cationic guar gum by ICP-MS. This method uses nitric acid-hydrogen peroxide and high-pressure vessel-assisted digestion technology to completely decompose difficult-to-process organic macromolecules through high temperature, high pressure and strong acid. The digested solution is then detected by ICP-MS, which can accurately and sensitively determine the characteristic elements in cationic guar gum, thereby achieving accurate analysis of the metal element content in cationic guar gum.

[0007] To address the problems in the prior art, this invention discloses a digestion method for the ICP-MS detection of cationic guar gum, comprising the following steps: S1. Accurate sample weighing: Accurately weigh 0.05-0.10 g of cationic guar gum sample using an analytical balance and place it in a clean polytetrafluoroethylene digestion vessel; S2. Pre-digestion: In a fume hood, add 5-8 mL of concentrated nitric acid to the digestion vessel using a pipette to ensure sufficient contact between the sample and the concentrated nitric acid. Cover the digestion vessel and let it stand in the fume hood for 12 hours; S3. Addition of oxidant: Add 1-2 mL of hydrogen peroxide to the digestion vessel; S4. High-pressure digestion: Completely seal the digestion vessel and place it in an oven. Set the high-pressure digestion program and perform digestion; S5. Post-treatment: After the digestion vessel has completely cooled to room temperature, transfer all the digestion solution to a volumetric flask and dilute to volume with ultrapure water for later use.

[0008] Preferably, the concentration of concentrated nitric acid in step S2 is 65-70%.

[0009] Preferably, the high-pressure tank digestion procedure in step S4 is as follows: target temperature 150-180℃, heating time 60min, holding time 4-6h, and natural cooling to room temperature.

[0010] More preferably, the high-pressure tank digestion procedure in step S4 is as follows: target temperature 150°C, heating time 60 min, holding time 4-6 h, and natural cooling to room temperature.

[0011] Preferably, in step S5, after all the digestion solution is transferred to the volumetric flask, the digestion vessel and inner cap are rinsed with ultrapure water at least 3 times, and all the washing solution is transferred into the volumetric flask.

[0012] On the other hand, the ICP-MS determination method using the above digestion method includes the following steps:

[0013] A1. Preparation of standard curve and internal standard solution: The standard stock solution is serially diluted with diluent to prepare standard points of 0 μg / L, 10 μg / L, 50 μg / L, 100 μg / L, and 200 μg / L, forming a series of standard curve solutions;

[0014] Dilute the internal standard stock solution to 100 μg / L;

[0015] A2. ICP-MS instrument conditions determination: (1) Turn on the ICP-MS and preheat for at least 30 minutes; use instrument tuning fluid to determine instrument parameters; (2) Use helium as the collision gas;

[0016] A3. Sample determination and data analysis: The internal standard solution was added online through a three-way valve, and the blank solution, standard curve series and the sample solution to be tested were measured in sequence. The concentration of the target element in the sample solution was calculated by ICP-MS software.

[0017] A4. Calculation of Results: Cationic Guar Gum Content (ppm) = (C sam -C bla ) × V × D / m, where C sam It is the elemental concentration and C measured in the sample solution. bla V is the element concentration measured in the blank solution, V is the sample volume, D is the dilution factor before measurement (or 1 if there is no dilution), and m is the sample mass.

[0018] Preferably, the diluent in step A1 is 2% nitric acid.

[0019] Preferably, the internal standard element in step A3 is one or more of Sc, Ge, In, and Rh.

[0020] The beneficial effects of this invention are as follows:

[0021] 1. In the pre-digestion process, concentrated nitric acid is used to slowly nitrate and oxidize the polymer, initially disrupting its three-dimensional network structure and long chains, effectively reducing sample viscosity and preventing agglomeration. The molecular structure of the pre-digested sample is loosened, allowing for faster and more thorough decomposition during subsequent high-pressure digestion, effectively preventing carbonization.

[0022] 2. After pre-digestion, hydrogen peroxide is added. Its strong oxidizing power, combined with nitric acid, effectively attacks and breaks stubborn chemical bonds such as C-C and CN bonds. This further oxidizes the intermediate products generated during pre-digestion (such as alcohols, aldehydes, and carboxylic acids) into CO2 and water, contributing to a colorless and clear final digestion solution.

[0023] 3. In the high-pressure digestion process, the guar gum matrix of organic matter is completely destroyed under the high temperature and pressure environment provided by the high-pressure vessel, allowing the target metal elements to completely dissolve and remain stably present in the acidic solution for ICP-MS analysis. This effectively prevents the loss of volatile elements, results in more thorough digestion, requires less reagent, and produces lower blank values.

[0024] 4. In ICP-MS detection, the use of collision gas greatly reduces background noise and significantly improves the signal-to-noise ratio.

[0025] 5. This invention utilizes safe and efficient sample pretreatment to completely and stably transfer the target element into solution, followed by accurate quantification using highly sensitive and interference-resistant analytical techniques. It perfectly combines high-pressure vessel digestion and ICP-MS collision reaction cell technology with online internal standard methods from modern analytical chemistry, systematically solving the challenges in the detection of cationic guar gum and achieving accurate, sensitive, stable, and high-throughput detection of characteristic elements in cationic guar gum. Detailed Implementation

[0026] The present invention will be further described below. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0027] The main instruments used in the digestion method for cationic guar gum detection by ICP-MS include: a high-pressure digestion vessel lined with polytetrafluoroethylene (PTFE), a forced-air drying oven / constant-temperature oven, a PTFE digestion inner vessel, ICP-MS, an analytical balance (0.01 g / mL), pipettes, a fume hood, and volumetric flasks. The main reagents used include: concentrated nitric acid (analytical grade), hydrogen peroxide (30%), laboratory-grade ultrapure water (resistivity ≥18.2 MΩ·cm), and standard stock solutions: standard solutions of the target element used to plot the standard curve; the internal standard stock solution is selected from elements that do not react with the sample and the analyte, such as Sc, Ge, In, or Rh.

[0028] Example 1: A digestion method for ICP-MS detection of cationic guar gum, comprising the following steps: S1. Accurate sample weighing: Accurately weigh 0.05 g of cationic guar gum sample using an analytical balance and place it in a clean polytetrafluoroethylene digestion vessel.

[0029] S2. Pre-digestion: In a fume hood, add 6 mL of concentrated nitric acid to the digestion vessel using a pipette, gently shake the vessel to wet the sample and ensure that the sample is in full contact with the concentrated nitric acid, cover the digestion vessel (but do not seal), and let it stand in the fume hood for 12 hours.

[0030] S3. Add oxidant: Add 2 mL of hydrogen peroxide to the digestion vessel. At this time, the reaction will be accelerated and bubbles will be generated.

[0031] S4. High-Pressure Digestion: Completely seal the digestion vessel and place it in an oven. Set the high-pressure digestion program and proceed with the digestion. The high-pressure digestion program for this step is as follows: target temperature 150℃, heating time 60 min, holding time 4 h, and natural cooling to room temperature.

[0032] S5. Post-processing: After the digestion vessel has completely cooled to room temperature, transfer all the digestion solution to a 50 mL volumetric flask. Rinse the digestion vessel several times with small amounts of ultrapure water, and add the washings to the volumetric flask. Finally, make up to volume, shake well, and prepare for testing. Prepare a reagent blank simultaneously.

[0033] When performing ICP-MS analysis on the digested sample, the following steps are included:

[0034] A1. Preparation of standard curve and internal standard solution: Dilute the standard stock solution stepwise with 2% diluent nitric acid to prepare standard points of 0 μg / L, 10 μg / L, 50 μg / L, 100 μg / L, and 200 μg / L, forming a series of standard curve solutions; dilute the internal standard stock solution to 100 μg / L.

[0035] A2. ICP-MS instrument conditions determination: (1) Turn on the ICP-MS and preheat for at least 30 min; use instrument tuning fluid to determine instrument parameters; (2) Use kinetic discrimination mode, use helium as collision gas, and the flow rate is 4.5 mL / min.

[0036] A3. Sample determination and data analysis: The internal standard solution was added online through a three-way valve, and the blank solution, standard curve series and the sample solution to be tested were measured in sequence. The concentration of the target element in the sample solution was calculated by ICP-MS software.

[0037] A4. Calculation of Results: Cationic Guar Gum Content (ppm) = (C sam -C bla ) × V × D / m, where C sam It is the elemental concentration and C measured in the sample solution.bla V is the element concentration measured in the blank solution, V is the sample volume, D is the dilution factor before measurement (or 1 if there is no dilution), and m is the sample mass.

[0038] Example 2: A digestion method for ICP-MS detection of cationic guar gum, comprising the following steps: S1. Accurate sample weighing: Accurately weigh 0.10 g of cationic guar gum sample using an analytical balance and place it in a clean polytetrafluoroethylene digestion vessel.

[0039] S2. Pre-digestion: In a fume hood, add 8 mL of concentrated nitric acid to the digestion vessel using a pipette, gently shake the vessel to wet the sample and ensure that the sample is in full contact with the concentrated nitric acid, cover the digestion vessel (but do not seal), and let it stand in the fume hood for 12 hours.

[0040] S3. Add oxidant: Add 1 mL of hydrogen peroxide to the digestion vessel. At this time, the reaction will be accelerated and bubbles will be generated.

[0041] S4. High-Pressure Digestion: Completely seal the digestion vessel and place it in an oven. Set the high-pressure digestion program and proceed with the digestion. The high-pressure digestion program for this step is as follows: target temperature 180℃, heating time 60 min, holding time 6 h, and natural cooling to room temperature.

[0042] S5. Post-processing: After the digestion vessel has completely cooled to room temperature, transfer all the digestion solution to a 50 mL volumetric flask. Rinse the digestion vessel several times with small amounts of ultrapure water, and add the washings to the volumetric flask. Finally, make up to volume, shake well, and prepare for testing. Prepare a reagent blank simultaneously.

[0043] When performing ICP-MS analysis on the digested sample, the following steps are included:

[0044] A1. Preparation of standard curve and internal standard solution: Dilute the standard stock solution stepwise with 2% diluent nitric acid to prepare standard points of 0 μg / L, 10 μg / L, 50 μg / L, 100 μg / L, and 200 μg / L, forming a series of standard curve solutions; dilute the internal standard stock solution to 100 μg / L.

[0045] A2. ICP-MS instrument conditions determination: (1) Turn on the ICP-MS and preheat for at least 30 min; use instrument tuning fluid to determine instrument parameters; (2) Use kinetic discrimination mode, use helium as collision gas, and the flow rate is 4.5 mL / min.

[0046] A3. Sample determination and data analysis: The internal standard solution was added online through a three-way valve, followed by the blank solution, standard curve series, and the sample solution to be tested in sequence. The concentration of the target element in the sample solution was calculated by ICP-MS software.

[0047] A4. Calculation of Results: Cationic Guar Gum Content (ppm) = (C sam -C bla ) × V × D / m, where C sam It is the elemental concentration and C measured in the sample solution. bla V is the element concentration measured in the blank solution, V is the sample volume, D is the dilution factor before measurement (or 1 if there is no dilution), and m is the sample mass.

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A digestion method for the detection of cationic guar gum by ICP-MS, characterized in that: Includes the following steps: S1. Accurate sample weighing: Accurately weigh 0.05-0.10g of cationic guar gum sample using an analytical balance and place it in a clean polytetrafluoroethylene digestion vessel; S2. Pre-digestion: In a fume hood, use a pipette to add 5-8 mL of concentrated nitric acid to the digestion vessel to ensure that the sample is in full contact with the concentrated nitric acid. Cover the digestion vessel and let it stand in the fume hood for 12 hours. S3. Add oxidant: Add 1-2 mL of hydrogen peroxide to the digestion vessel; S4. High-pressure digester digestion: Seal the digestion vessel completely and place it in an oven. Set the high-pressure digester digestion program and perform digestion. S5. Post-processing: After the digestion vessel has been completely cooled to room temperature, transfer all the digestion solution to a volumetric flask and dilute to volume with ultrapure water for later use.

2. The digestion method for cationic guar gum ICP-MS detection according to claim 1, characterized in that: In step S2, the concentration of concentrated nitric acid is 65-70%.

3. The digestion method for cationic guar gum ICP-MS detection according to claim 1, characterized in that: The high-pressure digestion procedure in step S4 is as follows: target temperature 150-180℃, heating time 60min, holding time 4-6h, and natural cooling to room temperature.

4. The digestion method for cationic guar gum ICP-MS detection according to claim 1, characterized in that: In step S5, after all the digestion solution has been transferred to the volumetric flask, the digestion vessel and inner cap are rinsed with ultrapure water at least 3 times, and all the washing solution is transferred to the volumetric flask.

5. The digestion method for cationic guar gum ICP-MS detection according to claim 3, characterized in that: The high-pressure digestion procedure in step S4 is as follows: target temperature 150℃, heating time 60min, holding time 4-6h, and natural cooling to room temperature.

6. The detection method for cationic guar gum ICP-MS detection using the digestion method described in any of the preceding claims, characterized in that: Includes the following steps: A1. Preparation of standard curve and internal standard solution: The standard stock solution is serially diluted with diluent to prepare standard points of 0 μg / L, 10 μg / L, 50 μg / L, 100 μg / L, and 200 μg / L, forming a series of standard curve solutions; Dilute the internal standard stock solution to 100 μg / L; A2. ICP-MS instrument conditions determination: (1) Turn on the ICP-MS and preheat for at least 30 minutes; use instrument tuning fluid to determine instrument parameters; (2) Use helium as the collision gas; A3. Sample determination and data analysis: The internal standard solution was added online through a three-way valve, and the blank solution, standard curve series and the sample solution to be tested were measured in sequence. The concentration of the target element in the sample solution was calculated by ICP-MS software. A4. Calculation of Results: Cationic guar gum content (ppm) = (C sam -C bla ) × V × D / m, where C sam It is the elemental concentration and C measured in the sample solution. bla V is the element concentration measured in the blank solution, V is the sample volume, D is the dilution factor before measurement (or 1 if there is no dilution), and m is the sample mass.

7. The detection method for cationic guar gum by ICP-MS according to claim 6, characterized in that: The diluent in step A1 is 2% nitric acid.

8. The detection method for cationic guar gum by ICP-MS according to claim 6, characterized in that: The internal standard element in step A3 is one or more of Sc, Ge, In, and Rh.