A pretreatment method for detecting arsenic-containing samples

Abstract

This invention discloses a pretreatment method for detecting arsenic-containing samples, comprising the following steps: S1. Drying the sludge sample, grinding and sieving it to obtain a pretreated sample; S2. Wetting the pretreated sample with deionized water, adding a digestion solution for digestion at normal pressure, and then using a hydrogen peroxide aqueous solution in boiling water for peroxidation reaction to obtain the sample to be tested; the digestion solution consists of concentrated hydrochloric acid, dilute perchloric acid, and dilute nitric acid; the sample to be tested is directly used for atomic spectroscopy to detect the arsenic content. The light source for atomic analysis spectroscopy is an inductively coupled high-frequency plasma torch. The method is simple, saves materials, has a low detection limit, and high repeatability.

Description

Technical Field

[0001] This invention relates to the field of heavy metal detection technology, and in particular to a pretreatment method for detecting arsenic-containing samples. Background Technology

[0002] Among metallic elements, heavy metals cannot be decomposed by microorganisms in soil and sediments, can accumulate continuously, and are enriched by organisms, passing through the food chain and posing a threat to humans. Some heavy metals can even be transformed into more toxic compounds by microorganisms in soil and sediment.

[0003] Inductively coupled plasma atomic emission spectrometry (ICP-AES) is a novel spectroscopic analysis method that uses an ICP-AES torch as the laser source. Due to its advantages such as low detection limits, high accuracy and precision, fast analysis speed, and wide linear range, it has become a widely applicable analytical method, suitable for the analysis and determination of the metallic element arsenic in soil. Before performing ICP-AES detection, soil pretreatment is required. This pretreatment process includes digestion, the purpose of which is to precipitate any heavy metal elements embedded in the soil.

[0004] Traditional methods for treating heavy metals in soil typically employ wet digestion, using sulfuric acid, perchloric acid, nitric acid, and hydrofluoric acid for complete soil digestion. However, since the acid dissolution efficiency of arsenic is not complete, the process requires multiple manual interventions, and determining the digestion endpoint requires extensive personal experience. Data reproducibility is poor, and the operation is time-consuming (more than 8 hours), material-intensive, and demands high levels of manual skill, making it unsuitable for the detection of large batches of samples. Furthermore, the spectral intensity of inductively coupled plasma torches is significantly lower than that of aqueous solutions due to interference from the acidity of the test solution and the viscosity of the diluent, resulting in a higher detection limit. Therefore, pretreatment with strong acids alone cannot meet the detection requirements of inductively coupled plasma atomic emission spectrometry.

[0005] Therefore, there is a need to provide a convenient and rapid pretreatment method for soil arsenic samples that ensures the detection limit of inductively coupled plasma atomic emission spectrometry. Summary of the Invention

[0006] In view of this, this application provides a pretreatment method for detecting arsenic-containing samples, which is simple in steps, saves materials, has a low detection limit, and has high repeatability.

[0007] To achieve the above technical objectives, this application adopts the following technical solution:

[0008] This application provides a pretreatment method for detecting arsenic-containing samples, including the following steps:

[0009] S1. After drying the sludge sample, grind and sieve it to obtain a pretreated sample;

[0010] S2. The pretreated sample is first moistened with deionized water, then digested with digestion solution at normal pressure, and then peroxidized in boiling water using hydrogen peroxide aqueous solution to obtain the sample to be tested.

[0011] The digestion solution is composed of concentrated hydrochloric acid, dilute perchloric acid, and dilute nitric acid; the sample to be tested is directly used for atomic spectroscopy to detect the arsenic content, and the light source for the atomic analysis spectrum is an inductively coupled high-frequency plasma torch.

[0012] Preferably, the concentration of the dilute nitric acid is 15-20%, and the concentration of the dilute perchloric acid is 5-10%.

[0013] Preferably, the sum of the volumes of the concentrated hydrochloric acid and the dilute perchloric acid is equal to the volume of the dilute nitric acid.

[0014] Preferably, the concentration of the hydrogen peroxide aqueous solution is 30-40%.

[0015] Preferably, the volume ratio of the hydrogen peroxide aqueous solution to the digestion solution is 3-5:1.

[0016] Preferably, the ratio of the pretreated sample to the digestion solution is 1g:10-20ml.

[0017] Preferably, the digestion time is 60-70 minutes.

[0018] Preferably, the digestion temperature is 90-95℃.

[0019] Preferably, the peroxidation reaction takes 1-2 hours.

[0020] Preferably, the average particle size of the pretreated sample is 100-120 mesh.

[0021] The beneficial effects of this application are as follows: The pretreatment method of this application can effectively dissolve arsenic in the soil, and the pretreatment time is greatly shortened (2h), eliminating the need for repeated digestion, saving materials (more than 60%), and is convenient and fast; at the same time, the digestion solution used in this application, in combination with hydrogen peroxide, reduces the interference of the digestion solution on the detector and ensures a low detection limit. On the other hand, the sample can be directly injected without dilution, which ensures the concentration of the sample to achieve high repeatability of the results while simplifying the detection process. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] As acidity increases, the intensity of spectral lines decreases significantly. Moreover, the inventors found that different inorganic acids have different effects on the intensity of spectral lines in inductively coupled plasma atomic emission spectrometry. However, diluting the sample solution to reduce acidity leads to an increase in the detection limit. If the solution is not diluted, in addition to the effect of acidity on the inductively coupled plasma torch, the viscosity of the sample is also too high, making it difficult to inject the sample using pneumatic nebulization, which can clog the instrument. Selecting a suitable digestion solution and performing appropriate post-treatment can overcome this difficulty and also reduce the number of digestion steps and time.

[0024] Based on this, the present invention was created.

[0025] This application provides a pretreatment method for detecting arsenic-containing samples, including the following steps:

[0026] S1. After drying the sludge sample, grind and sieve it to obtain a pretreated sample;

[0027] S2. The pretreated sample is first moistened with deionized water, then digested with digestion solution at normal pressure, and then peroxidation reaction is carried out using hydrogen peroxide aqueous solution in boiling water bath to obtain the sample to be tested.

[0028] The digestion solution consists of concentrated hydrochloric acid, dilute perchloric acid, and dilute nitric acid; the sample to be tested is directly used for atomic spectroscopy to detect the arsenic content, and the light source for atomic analysis spectroscopy is an inductively coupled high-frequency plasma torch.

[0029] In this digestion solution, nitric acid disrupts the soil's crystal structure, causing embedded heavy metals to precipitate. Perchloric acid destroys the organic matter in the soil, releasing heavy metals from the humus formed within plants and animals. Hydrochloric acid corrodes the soil, further dissolving arsenic. Regarding the influence of hydrochloric acid, nitric acid, perchloric acid, and hydrofluoric acid on the spectral line intensity, the inventors found that the effects of hydrochloric acid, nitric acid, perchloric acid, and hydrofluoric acid on the spectral line intensity increase in that order. Therefore, the concentrations of perchloric acid and nitric acid were reduced to minimize their impact, while a high concentration of hydrochloric acid was used to compensate for the insufficient digestion kinetics caused by perchloric acid and nitric acid. Hydrogen peroxide is then used for peroxidation. Based on the digestion solution, the peroxidation reaction facilitates the precipitation of heavy metals. Simultaneously, the peroxidation reaction decomposes hydrogen peroxide into water, diluting the acid concentration and reducing the impact of the digestion solution's acidity and viscosity on the spectral line intensity, thus ensuring accuracy.

[0030] On the other hand, since the volume of hydrogen peroxide does not change after the peroxidation reaction, the concentration of the sample is guaranteed, and the results of arsenic detection by inductively coupled plasma atomic emission spectrometry have high repeatability and strong stability.

[0031] In some embodiments, the concentration of dilute nitric acid is 15-20%, and the concentration of dilute perchloric acid is 5-10%.

[0032] In some embodiments, the sum of the volumes of concentrated hydrochloric acid and dilute perchloric acid is equal to the volume of dilute nitric acid.

[0033] In the early stages of soil sample digestion, perchloric acid is essential. However, as digestion progresses, perchloric acid reacts with nitric acid. Nitric acid gains a proton in perchloric acid and becomes alkaline, thus reducing the digestive effect of nitric acid on the soil. Furthermore, perchloric acid reacts with low-valence nitrogen oxides contained in nitric acid, which also reduces the digestive effect of perchloric acid on the soil. Therefore, in this scheme, the concentration and amount of dilute nitric acid are greater than those of dilute perchloric acid to overcome this deficiency.

[0034] In some embodiments, the concentration of the hydrogen peroxide aqueous solution is 30-40%, and the volume ratio of the hydrogen peroxide aqueous solution to the digestion solution is 3-5:1; too low a concentration or amount will lead to incomplete peroxidation reaction, while too high a concentration will reduce the concentration of the test solution.

[0035] In some embodiments, the ratio of pretreated sample to digestion solution is 1g:10-20ml.

[0036] In some embodiments, the digestion time is 60-70 min; the digestion temperature is 90-95 °C; and the peroxidation reaction time is 1-2 h. Under these conditions, the time and materials used are most economical, and the arsenic in the soil can be fully dissolved without being lost due to excessively high temperatures.

[0037] In some embodiments, the average particle size of the pretreated sample is 100-120 mesh. If the particle size is too low, there will be a loss of arsenic, and if the particle size is too high, the digestion will be incomplete.

[0038] In this scheme, concentrated nitric acid, concentrated hydrochloric acid, concentrated perchloric acid, and pure hydrogen peroxide are all analytical grade pure solutions with a concentration greater than 98%, and dilute nitric acid, dilute hydrochloric acid, dilute perchloric acid, and hydrogen peroxide aqueous solutions are all obtained by diluting the corresponding concentrated solutions with deionized water.

[0039] The samples to be treated mentioned in Examples 1-3 and Comparative Examples 1-2 were mud samples with arsenic content of 0, to which standard arsenic was added sequentially at concentrations of 2, 6, 8, and 10 mg / kg.

[0040] The present application will be further described below through specific embodiments.

[0041] Example 1

[0042] A pretreatment method for detecting arsenic-containing samples includes the following steps:

[0043] S1. Spread the wet sludge sample evenly on a ceramic tray, press it with a glass rod, etc., to remove stones, animal and plant remains and other foreign matter from the sludge sample, then mix it well. In a drying room (south-facing, protected from direct sunlight, well-ventilated, clean and dust-free, free of volatile chemicals), place the mixed sample on a drying tray to spread it into a thin layer of 2-3 cm and air dry for later use. In the grinding room, pour the air-dried sample onto an acrylic plate, tap it with a wooden hammer, and crush it again with a wooden roller, wooden stick and acrylic rod, pick out impurities, mix it well, and use the quartering method to take a crushed sample and pass it through a 0.25 mm (20 mesh) nylon sieve. Place all the sieved sample on a colorless polyethylene film and stir it thoroughly. Then use the quartering method to take two portions. One portion is placed in the sample storage, and the other portion is used for fine grinding. Divide the sample into two portions again using the quartering method. Grind one portion until it passes through a 100 mesh sieve to obtain the pretreated sample.

[0044] S2. Place 0.5g of the pretreated sample into a 50mL stoppered colorimetric tube, add 1mL of deionized water to wet the sample, add 10mL of digestion solution and digest at 90℃ for 60min, shaking several times during digestion. After cooling, add 30mL of hydrogen peroxide and heat to carry out the peroxidation reaction. Then, react again in a boiling water bath for 1h. After cooling, dilute the sample to a 50mL volumetric flask to obtain the test sample. The test sample is directly used for atomic spectroscopy to detect the arsenic content. The light source for the atomic analysis spectroscopy is an inductively coupled high-frequency plasma torch. The concentration of the dilute nitric acid is 15%, the concentration of the dilute perchloric acid is 5%, the concentration of the hydrogen peroxide is 30%, and the sum of the volumes of the concentrated hydrochloric acid and the dilute perchloric acid is equal to the volume of the dilute nitric acid.

[0045] Example 2

[0046] A pretreatment method for detecting arsenic-containing samples includes the following steps:

[0047] S1. Spread the wet sludge sample evenly on a ceramic tray, press it with a glass rod, etc., to remove stones, animal and plant remains and other foreign matter from the sludge sample, then mix it well. In a drying room (south-facing, protected from direct sunlight, well-ventilated, clean and dust-free, free of volatile chemicals), place the mixed sample on a drying tray to spread it into a thin layer of 2-3 cm and air dry for later use. In the grinding room, pour the air-dried sample onto an acrylic plate, tap it with a wooden hammer, and crush it again with a wooden roller, wooden stick and acrylic rod, pick out impurities, mix well, and use the quartering method to take a crushed sample and pass it through a 0.25 mm (20 mesh) nylon sieve. Place all the sieved samples on a colorless polyethylene film and stir thoroughly. Then use the quartering method to take two portions. One portion is placed in the sample storage, and the other portion is used for fine grinding. Divide the sample into two portions again using the quartering method. Grind one portion until it passes through a 120 mesh sieve to obtain the pretreated sample.

[0048] S2. 1 g of the pretreated sample is placed in a 50 mL stoppered colorimetric tube, moistened with 1 mL of deionized water, and 10 mL of digestion solution is added. The sample is digested at 95 °C for 70 min, with several shakings during digestion. After cooling, 50 mL of hydrogen peroxide is added and heated to carry out the peroxidation reaction. The reaction is then carried out again in a boiling water bath for 2 h. After cooling, the sample is diluted to a 50 mL volumetric flask to obtain the test sample. The test sample is directly used for atomic spectroscopy to detect the arsenic content. The light source for the atomic analysis spectroscopy is an inductively coupled high-frequency plasma torch. The concentration of the dilute nitric acid is 20%, the concentration of the dilute perchloric acid is 10%, the concentration of the hydrogen peroxide is 40%, and the sum of the volumes of the concentrated hydrochloric acid and the dilute perchloric acid is equal to the volume of the dilute nitric acid.

[0049] Example 3

[0050] A pretreatment method for detecting arsenic-containing samples includes the following steps:

[0051] S1. Spread the wet sludge sample evenly on a ceramic tray, press it with a glass rod, etc., to remove stones, animal and plant remains and other foreign matter from the sludge sample, then mix it well. In a drying room (south-facing, protected from direct sunlight, well-ventilated, clean and dust-free, free of volatile chemicals), place the mixed sample on a drying tray to spread it into a thin layer of 2-3 cm and air dry for later use. In the grinding room, pour the air-dried sample onto an acrylic plate, tap it with a wooden hammer, and crush it again with a wooden roller, wooden stick and acrylic rod, pick out impurities, mix well, and use the quartering method to take a crushed sample and pass it through a 0.25 mm (20 mesh) nylon sieve. Place all the sieved samples on a colorless polyethylene film and stir thoroughly. Then use the quartering method to take two portions. One portion is placed in the sample storage, and the other portion is used for fine grinding. Divide the sample into two portions again using the quartering method. Grind one portion until it passes through a 110 mesh sieve to obtain the pretreated sample.

[0052] S2. 0.8 g of the pretreated sample is placed in a 50 mL stoppered colorimetric tube, moistened with 1 mL of deionized water, and then digested in 95 °C for 70 min with several shakings during digestion. After cooling, 40 mL of hydrogen peroxide is added and heated to induce peroxidation. The mixture is then reacted again in a boiling water bath for 1 h. After cooling, the sample is diluted to a 50 mL volumetric flask to obtain the test sample. This test sample is directly used for atomic spectroscopy to detect the arsenic content. The light source for the atomic analysis spectroscopy is an inductively coupled high-frequency plasma torch. The concentration of the dilute nitric acid is 20%, the concentration of the dilute perchloric acid is 10%, the concentration of the hydrogen peroxide is 35%, and the sum of the volumes of the concentrated hydrochloric acid and the dilute perchloric acid is equal to the volume of the dilute nitric acid.

[0053] Comparative Example 1

[0054] A pretreatment method for detecting arsenic-containing samples is the same as in Example 1, except that the concentrated hydrochloric acid, dilute perchloric acid, and dilute nitric acid in the digestion solution are replaced with concentrated hydrochloric acid, concentrated perchloric acid, and concentrated nitric acid, the digestion time is 3 hours, and hydrogen peroxide is not used for peroxidation reaction after digestion.

[0055] Comparative Example 2

[0056] A pretreatment method for detecting arsenic-containing samples is the same as in Example 1, except that the concentrated hydrochloric acid, dilute perchloric acid, and dilute nitric acid in the digestion solution are replaced with concentrated hydrochloric acid, concentrated perchloric acid, and concentrated nitric acid.

[0057] Evaluation Test

[0058] The test samples obtained in Examples 1-3 and Comparative Examples 1-2 were directly aspirated into an emission spectrometer (ICP-OES Avio200) using an inductively coupled plasma torch as the light source; deionized water was used as a substitute for the test sample, and the same steps and reagents as in Example 1 were used as a blank control; the analyte arsenic volatilized, atomized, excited, and emitted characteristic spectral lines in the torch, and the concentration of arsenic in the test sample was determined based on the intensity of the spectral lines, and the method detection limit was obtained. The results are shown in Table 1; 2 mg / ml of standard arsenic was added to Examples 1-3 and Comparative Examples 1-2, and the recovery rate was tested, as shown in Table 1.

[0059] Table 1 Test Results

[0060] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Method detection limit (mg / kg) 1.7 1.9 1.8 4.2 3.5 Recovery rate (%) 101 99 102 82 86

[0061] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A pretreatment method for detecting arsenic-containing samples, characterized in that, Includes the following steps: S1. After drying the sludge sample, grind and sieve it to obtain a pretreated sample; S2. The pretreated sample is first moistened with deionized water, then digested with digestion solution at normal pressure, and then peroxidized in boiling water using hydrogen peroxide aqueous solution to obtain the sample to be tested. The digestion solution is composed of concentrated hydrochloric acid, dilute perchloric acid, and dilute nitric acid; the sample to be tested is directly used for atomic spectroscopy to detect the arsenic content, and the light source for the atomic analysis spectroscopy is an inductively coupled high-frequency plasma torch; the concentration of the dilute nitric acid is 15-20%, and the concentration of the dilute perchloric acid is 5-10%; the sum of the volumes of the concentrated hydrochloric acid and the dilute perchloric acid is equal to the volume of the dilute nitric acid.

2. The pretreatment method for detecting arsenic-containing samples according to claim 1, characterized in that, The concentration of the hydrogen peroxide aqueous solution is 30-40%.

3. The pretreatment method for detecting arsenic-containing samples according to claim 2, characterized in that, The volume ratio of the hydrogen peroxide aqueous solution to the digestion solution is 3-5:

1.

4. The pretreatment method for detecting arsenic-containing samples according to claim 1, characterized in that, The ratio of the pretreated sample to the digestion solution is 1g:10-20ml.

5. The pretreatment method for detecting arsenic-containing samples according to claim 1, characterized in that, The digestion time is 60-70 minutes.

6. The pretreatment method for detecting arsenic-containing samples according to claim 1, characterized in that, The digestion temperature is 90-95℃.

7. The pretreatment method for detecting arsenic-containing samples according to claim 1, characterized in that, The peroxidation reaction takes 1-2 hours.

8. The pretreatment method for detecting arsenic-containing samples according to claim 1, characterized in that, The average particle size of the pretreated sample is 100-120 mesh.