Method for detecting lead content in plant based on combination of switchable hydrophobic deep eutectic solvent and ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometer)

Abstract

The invention discloses a method for detecting the content of lead in a plant based on the combination of a switchable hydrophobic deep eutectic solvent and ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometer). The invention establishes a method for combining an in-situ generated fatty acid-based switchable hydrophobic depth eutectic solvent FA-SSDES and an inductively coupled plasma emitter spectrometer ICP-OES, and the method is used for measuring trace Pb in Yunnan pinellia ternate. An extraction solvent and a foaming agent are pressed into tablets and transferred into an aqueous solution, and meanwhile, SHDES and CO2 are generated in situ through reaction, so that rapid dispersion and one-step extraction of trace lead are realized. Under the optimal condition, the enrichment factor EF of the method reaches 31, and the detection limit and the quantitation limit are 0.15 mu g / L and 0.50 mu g / L respectively. The detection method is simpler, more convenient and quicker to operate, and has great potential in detection of metal ions in complex matrix samples and medicinal materials.

Description

Technical Field

[0001] The invention belongs to the field of analytical chemistry, and in particular relates to a method for detecting lead content in plants based on the combination of a switchable deep eutectic solvent and ICP-OES. Background Art

[0002] Pinellia Pinellia ternata (Thunb.) Breit.) is a perennial herbaceous plant of the Araceae family. Its medicinal part is the dried tuber, which includes a variety of nucleosides, {Li, 2022 #38} organic acids, flavonoids, amino acids and other ingredients. It has antitussive and expectorant, antiemetic, coagulation, anti-tumor, antioxidant, antibacterial and other effects. However, with the development of human activities, economy and industry, heavy metal pollution in soil, water and air has caused Chinese herbal medicines to be polluted by heavy metals from different aspects. Among them, lead is a highly toxic heavy metal that is widely distributed in the environment. Even a small amount of Pb can damage the nervous system and cause diseases such as Alzheimer's disease and Parkinson's disease. The accumulation of lead in the body can damage the digestive system, cardiovascular system, nervous system, hematopoietic stem cells, immune system and reproductive system, especially has an irreversible effect on children's neurodevelopment. Therefore, it is necessary to establish a simple, accurate and sensitive analytical method for determining the content of Pb in medicinal materials.

[0003] At present, the methods used for determining the content of metal elements include atomic fluorescence spectrometry (AFS), flame atomic absorption spectrometry (FAAS), graphite furnace atomic absorption spectrometry (GFAAS), inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS), among which ICP-OES is a commonly used elemental analysis method with the advantages of low cost, fast analysis speed, wide linear range and high sensitivity. Due to the complex matrix of the analyzed samples and the low content of the target elements, it is difficult for the instrument to directly and accurately determine the content of the target elements in the samples, and it is necessary to combine the pretreatment method to concentrate, enrich and separate the target analytes in the samples.

[0004] In recent years, deep eutectic solvents (DES) have been considered as a new type of environmentally friendly green solvent due to their low toxicity, low cost, easy preparation, good biocompatibility, and strong extraction ability. However, the application of hydrophobic DES is greatly limited due to its non-volatility, difficulty in separation, and wide application in phase separation in polar media. However, the emergence of a new generation of green solvents, switchable deep eutectic solvents (SDES), has solved this problem. SDES can switch between affinity and phobia, and between polarity and non-polarity according to different external driving factors (pH, temperature, CO2, etc.), and is often used for the separation and enrichment of organic pollutants. However, there are no reports on the SHDES-ME method for the enrichment and separation of heavy metals. Summary of the invention

[0005] The purpose of the present invention is to provide a method for detecting the lead content in plants based on the combination of a switchable hydrophobic deep eutectic solvent and ICP-OES. The method can achieve in-situ synthesis of extraction solvent and CO2, Pb extraction and phase separation in one step, and the operation is simpler and faster.

[0006] In order to achieve the above-mentioned invention object, the present invention adopts the following technical solutions: The present invention provides a method for detecting lead content in plants based on a switchable hydrophobic deep eutectic solvent combined with ICP-OES, comprising the following steps: (1) The plant sample is crushed and sieved, and then digested with an acidic solution. After digestion, the acid is removed to obtain the plant sample to be tested; (2) The SHDES precursor, proton donor, effervescent agent and lead complexing agent are mixed evenly, subjected to ultrasonic treatment and heating, and the aqueous phase is removed by centrifugation. The obtained organic phase is resolved with an acidic solution, and the aqueous phase is taken by centrifugation to obtain FA-SHDES-ME; (3) The plant sample to be tested in step (1) and the FA-SHDES-ME in step (2) are mixed for enrichment, and the lead content in the plant sample is determined by ICP-OES.

[0007] Furthermore, the SHDES precursor includes HBA and HBD; the HBA is at least one of choline chloride, tetrabutylammonium bromide, thymol, and acetylcholine chloride; the HBD is sodium octanoate; and the mass ratio of the HBA to the HBD is 1:1-3.

[0008] Preferably, the HBA is choline chloride; the mass ratio of the choline chloride to sodium octanoate is 1:2.

[0009] Furthermore, the proton donor is malonic acid; the effervescent agent is sodium bicarbonate; and the lead complexing agent is dithizone.

[0010] Furthermore, the dosage of sodium octanoate is 400-800 mg.

[0011] Preferably, the dosage of sodium octanoate is 800 mg Furthermore, the dosage of malonic acid is 650-750 mg.

[0012] Preferably, the amount of malonic acid used is 650 mg.

[0013] Furthermore, the dosage of the sodium bicarbonate is 600-800 mg.

[0014] Preferably, the amount of sodium bicarbonate used is 800 mg.

[0015] Furthermore, the concentration of dithizone is 0.5×10 -5 mol / L–1.0×10 -5 mol / L.

[0016] Preferably, the concentration of dithizone in the solution is 1.0×10 –5 mol / L.

[0017] Furthermore, the ultrasonic treatment time is 15-20 min.

[0018] Preferably, the ultrasonic treatment time is 20 min.

[0019] Furthermore, the volume ratio of the plant sample to be tested to FA-SHDES-ME is 1:1-10.

[0020] Furthermore, the acidic solution is nitric acid.

[0021] Furthermore, the plant is Pinellia ternata.

[0022] Furthermore, the detection limit of the method is 0.15 μg / L, and the quantification limit is 0.50 μg / L.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The present invention successfully established a new method for extracting Pb by FA-SHDES-ME and combined it with ICP-OES to determine trace Pb in Yunnan Pinellia. This is the first time that FA-SHDES-ME and ICP-OES have been combined for the extraction and analysis of trace Pb in Yunnan Pinellia.

[0024] 2. The method uses bubbles to assist in the in-situ generation of a hydrophobic switchable solvent, quickly and evenly disperses SHDES into the solution, and achieves Pb enrichment and separation in one step.

[0025] 3. The method has low LOD, LOQ and RSD, good EF and R 2 ,The lead content in Pinellia ternata can be accurately determined by FA-SHDES-ME combined with ICP-OES detection, and it has great potential in the detection of metal ions in complex matrix samples and medicinal materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Infrared spectra of choline chloride, sodium octanoate and SHDES.

[0027] Figure 2 Optimize results for SHDES type.

[0028] Figure 3Optimize results for sodium caprylate dosage.

[0029] Figure 4 This is the result of malonic acid dosage.

[0030] Figure 5 This is the result of sodium bicarbonate dosage.

[0031] Figure 6 This is the result of dithizone dosage.

[0032] Figure 7 Ultrasonic time results. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described in detail with reference to the following specific examples.

[0034] In the following examples, unless otherwise specified, the experimental methods used are all conventional methods, and the materials and reagents used can be purchased from biological or chemical reagent companies.

[0035] The present invention uses SHDES precursors (choline chloride and sodium octanoate), proton donors (malonic acid) and effervescent agents (sodium bicarbonate) to prepare extraction solvents and foaming agents. Malonic acid plays two roles. First, malonic acid provides an acidic environment. When the system solution pH < pKa （辛酸钠） When the reaction is carried out, sodium octanoate reacts with malonic acid to generate octanoic acid, and the octanoic acid and choline chloride (ChCl) are ultrasonically heated to form a hydrogen bond network to generate SHDES in situ, and the Pb-DTZ (dithizone) complex is extracted. Secondly, malonic acid acts as a proton donor for bubbling. It reacts with sodium bicarbonate to generate CO2 in situ, which disperses the formed SHDES droplets and accelerates the mass transfer rate between the analyte and the extraction solvent, while increasing the contact area between the extractant and the target analyte, promoting the extraction of the analyte.

[0036] The mechanism of the ETA-SHDES-ME method is as follows: , Compared with the traditional SHDES-DLLME, the FA-SHDES-ME used in the present invention can realize the in-situ generation of extraction solvent and CO2, quickly achieve phase equilibrium, and complete Pb extraction and separation.

[0037] Example 1 1. Method for detecting lead content in Pinellia ternata by combining switchable deep eutectic solvents with ICP-OES 1. Preparation of plant sample solution to be tested The medicinal material Pinellia ternata was collected from Dali, Yunnan, and was identified as the root of Pinellia ternata. After the sample was collected, the medicinal material was washed with pure water, dried, crushed, and sieved. Accurately weigh 0.5000 g of medicinal material powder in a digestion tube, and HNO3 (8.0 mL), H2O2 (30%, 2.0 mL) and ultrapure water (2.0 mL) were added in turn. The sample was digested using a microwave digester. The digested sample was placed on an acid extractor at 130°C for about 3.5 h to remove acid. Subsequently, the solution was clarified, cooled to room temperature, and the solution was transferred to a 10.0 mL volumetric flask to make up the volume, and the plant sample solution to be tested was obtained.

[0038] 2. Process of lead detection by SHDES-ME combined with ICP-OES Add dithizone (the concentration of dithizone is 1.0×10 –5 mol / L), followed by adding tablets compressed from 400 mg choline chloride (HBA), 800 mg sodium octanoate (HBD), 650 mg malonic acid and 800 mg sodium bicarbonate, placing in a 50°C aqueous solution for ultrasonic heating for 20 min, discarding the aqueous phase, and analyzing the target elements in the organic phase with 2 mol / L HNO3 solution. Centrifuging at 4000 r / min, taking 1.5 mL of the aqueous phase, and determining the Pb in the aqueous phase by ICP-OES.

[0039] 3. Determination of Pb in samples The established SHDES-ME method was used to enrich the plant sample solution after digestion and deacidification, and then the lead content in the Pinellia sample was determined using Optima 8000 ICP-OES. The operating conditions are shown in Table 1.

[0040] Table 1 Optimal instrument parameters for ICP-OES

[0041] 2. Characterization of switchable deep eutectic solvents In order to confirm the in situ synthesis of hydrophobic SDES, choline chloride, octanoic acid and SHDES were characterized by infrared spectroscopy (FTIR). Figure 1 As shown. At 3408 cm –1 and 1086 cm –1 The stretching vibration peaks of -OH and CN of choline chloride were observed at 1700 cm –1 The vibration peak at 3408 cm-1 is attributed to the stretching vibration of C=O. In the spectrum of SDES, the vibration peak of -OH was observed to be red-shifted (from 3408 cm-1 to –1 Move to 3388 cm –1) and the vibration absorption band becomes wider, indicating that hydrogen bonds are formed between choline chloride and octanoic acid, which changes the bond force constant of OH between SHDES.

[0042] 3. Condition Optimization 1. SHDES type The extraction solvent used in the microextraction process of in situ generation of hydrophobic switchable deep eutectic solvents must exhibit acid-base switchable hydrophilicity, and HBA and HBD form SHDES. Based on the in situ formation of SHDES and the switchable process, sodium octanoate was selected as HBD (sodium octanoate reacts with malonic acid to form octanoic acid, and octanoic acid reacts with HBA under water bath heating to form SHDES). Therefore, in this experiment, the SHDES with the best extraction effect was selected from SHDES-1 (choline chloride: sodium octanoate, 1:2), SHDES-2 (tetrabutylammonium bromide: sodium octanoate, 1:3), SHDES-3 (thymol: sodium octanoate, 1:1), and SHDES-4 (acetylcholine chloride: sodium octanoate, 1:2) as the extraction solvent for Pb. Figure 2 As shown in the figure, SHDES-1 has the highest signal intensity value among the four SHDES. Therefore, SHDES-1 was selected as the extraction solvent for subsequent experiments.

[0043] 2. Dosage of Sodium Caprylate In the method of the present invention, the amount of fatty acid salt used will directly affect the proportion of HBD in SHDES and the volume of the extraction solvent, thereby affecting the extraction effect. By adjusting the pH of the solution system to a value lower than the pKa of octanoic acid through a proton donor, sodium octanoate can be converted into octanoic acid, providing HBD for the formation of SHDES. Figure 3 It can be seen that with the increase in the amount of sodium octanoate, the signal intensity of the extracted target gradually increases. When sodium octanoate is excessive, a dilution effect occurs in the solution, resulting in a decrease in the extraction performance. When the amount of sodium octanoate is 800 mg, the signal intensity value is the highest. Therefore, 800 mg of sodium octanoate was selected for subsequent experiments.

[0044] 3. Proton donor dosage In the method of the present invention, malonic acid not only provides an acidic environment, but also reacts with sodium octanoate in the solution to generate octanoic acid droplets, which are then reacted with choline chloride to generate an extraction solvent (SHDES) in situ. The amount of malonic acid used affects the octanoic acid generation content and the dispersion of the hydrophobic SDES droplets, directly affecting the volume of the extraction solvent and the contact area between the extraction solvent and the target, further affecting the extraction effect of the target. Therefore, it is important to explore the effect of the amount of malonic acid on the extraction effect of the analyte. Figure 4The results show that when the amount of malonic acid is less than 650 mg, sodium octanoate is not completely converted into octanoic acid droplets, resulting in poor extraction effect. When the amount of malonic acid is greater than 650 mg, the system solution is strongly acidic, which may destroy the complex, causing the extraction effect to gradually decrease. When the amount of malonic acid is 650 mg, the signal intensity value is the highest. The results show that 650 mg of malonic acid is selected as the optimal amount for subsequent experiments.

[0045] 4. Dosage of sodium bicarbonate The CO2 generated in situ by the foaming agent and proton donor during the microextraction process is beneficial to the dispersion of the extraction solvent in the aqueous phase and promotes the mass transfer of the target to SHDES. In this experiment, sodium bicarbonate was used as the foaming agent and malonic acid was used as the proton donor. Among them, the amount of the foaming precursor is the key parameter affecting the generation of bubbles. In order to determine the optimal amount of sodium bicarbonate, different amounts (from 200 mg to 1200 mg) were explored. Figure 4 It can be seen that when the amount of sodium bicarbonate is insufficient, the foaming rate will slow down, thus affecting the dispersion effect and mass transfer efficiency of the extractant. However, excessive sodium bicarbonate will consume malonic acid excessively, resulting in a reduction in the volume of the organic phase, and there will not be enough organic phase to extract the target, resulting in a decrease in extraction efficiency. Therefore, 800 mg of sodium bicarbonate is the optimal amount.

[0046] 5. Dithizone concentration When dithizone is selected as the complexing agent for Pb, its concentration is important to ensure complete complexation of Pb. –6 The influence on the Pb response intensity value in the mol / L range is as follows: Figure 5 The results showed that the concentration of dithizone was 1.0–10.0×10 –6 mol / L, the response intensity value gradually increased, and the dithizone concentration continued to increase (1.0–2.5×10 –5 mol / L), the response intensity of Pb gradually decreased, and the concentration was 1.0×10 –5 mol / L, the response intensity value is the best. At low concentrations, Pb complexation is incomplete, and at high concentrations, co-extraction occurs, and the excess complexing agent is extracted into the organic phase, reducing the Pb extraction effect. Therefore, 1.0×10 -5 mol / L dithizone is the best complexing agent.

[0047] 6. Ultrasound time The duration of ultrasound exposure mainly affects the construction of the hydrogen bond network between choline chloride and octanoic acid, and directly determines the volume of the extraction solvent. In order to obtain the optimal ultrasound time, the effect of ultrasound time on the extraction efficiency was investigated within 10–40 min. The results are shown in Figure 2. Figure 6As shown in the figure, within the range of 10–20 min, the analyte extraction efficiency gradually increased. Ultrasonic time exceeding 20 min may affect the mass transfer rate between the analyte and the SHDES droplets, and the extraction efficiency decreases. It also shows that within 20 min, the hydrophobic SDES droplets are quickly formed and reach the extraction equilibrium state. Therefore, the optimal ultrasonic time is selected as 20 min.

[0048] 4. Interference Since the actual sample matrix is ​​complex and contains many common matrix ions and metal ions, they may compete with Pb and affect the extraction efficiency of Pb-DTZ. In order to investigate the anti-interference ability of FA-SHDES-ME. Under the optimal experimental conditions, different concentrations of interfering ions were added to the analysis solution containing 20μg / L Pb to study the effect of coexisting ions on the extraction recovery of Pb (the recovery rate was maintained at 90–110%, which can be regarded as no interference). The results are shown in Table 2. It can be seen from the table that common matrix ions have little effect on the extraction efficiency of Pb. For other metal ions, their allowable limits are lower due to competition and co-extraction.

[0049] Table 2 Tolerance of coexisting ions in lead determination (20.0 μg / L, n = 3)

[0050] 5. Analytical performance Under the optimal conditions, the analytical performance of the established FA-SHDES-ME was evaluated, and the results are shown in Table 3. Correlation coefficient R 2 The linear relationship was good. The limit of detection (LOD) and the limit of quantification (LQD) of FA-SHDES-ME were 0.15 μg / L and 0.50 μg / L, respectively, and the enrichment factor (EF) was 31. Compared with the direct determination results of inductively coupled plasma emission mass spectrometer (ICP-MS), the inter-day density was 0.39% and the intra-day precision was 1.02%. The results showed that this method has high sensitivity, good precision and is easy to operate.

[0051] Table 3 Analytical performance of lead determination

[0052] 6. Determination of Pb in actual samples The applicability of this method was investigated by analyzing the lead content in Yunnan Pinellia. The sample was crushed and sieved, microwave digested, and the digested product was enriched with FA-SHDES-ME and determined by ICP-OES. The determination results were consistent with those of direct ICP-MS determination, as shown in Table 4. The sample recovery rate was within the acceptable range of 93.0–104%, verifying the feasibility and accuracy of the FA-SHDES-ME method. This method has lower LOD, LOQ and RSD, and obtains better EF and R 2 .

[0053] Table 4 Analysis results of lead in actual samples (average value ± standard deviation of three replicates)

[0054] In summary, the present invention successfully established a new method for extracting Pb by FA-SHDES-ME, and combined it with ICP-OES to determine trace Pb in Yunnan Pinellia. This method uses bubbles to assist in the in-situ generation of hydrophobic switchable solvents, quickly and evenly disperses SHDES into the solution, and achieves Pb enrichment and separation in one step. The results show that this method has low LOD, LOQ and RSD, and good EF and R 2 , the lead content in Yunnan Pinellia can be accurately determined by FA-SHDES-ME combined with ICP-OES detection. Therefore, the method of the present invention has great potential in the detection of metal ions in complex matrix samples and medicinal materials.

[0055] Example 2 Using the optimized parameters obtained in Example 1, the present invention provides a method for detecting the lead content in Pinellia ternata based on a switchable hydrophobic deep eutectic solvent combined with ICP-OES, comprising the following steps: 1. Sample collection and preparation Collect the root of Pinellia ternata, wash it with pure water, dry it, crush it and sieve it. Accurately weigh 0.5000 g of sample powder in a digestion tube, and add 8.0 mL HNO3, 2.0 mL H2O2 (volume fraction of 30%) and 2.0 mL ultrapure water in turn. Use a microwave digestion instrument to digest the sample. The digested sample is placed in an acid extractor at 130℃ for 3.5 h to remove acid. Then, wait for the solution to clarify, cool it to room temperature, transfer the solution to a 10.0 mL volumetric flask and make up the volume to obtain the sample to be tested.

[0056] 2. Add 400 mg choline chloride, 800 mg sodium octanoate, 650 mg malonic acid, 800 mg sodium bicarbonate, and a concentration of 1.0 × 10 -5After the mol / L dithizone solution was mixed evenly, it was placed in a 50°C aqueous solution and ultrasonically heated for 20 min. Then, all the aqueous phase was removed by a high-speed centrifuge, leaving the organic phase. The organic phase was then decomposed with 2M HNO3 and centrifuged at 4000 r / min. 1.5 mL of the aqueous phase was taken to obtain FA-SHDES-ME.

[0057] 3. FA-SHDES-ME and the sample to be tested were mixed in a volume ratio of 1:1 for enrichment, and the lead content of the Pinellia sample was determined by ICP-OES. The instrument parameters of ICP-OES are shown in Table 1.

[0058] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for a person skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to replace some of the technical features therein by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions claimed to be protected by the present invention.

Claims

1. A method for detecting lead content in plants based on a switchable hydrophobic deep eutectic solvent combined with ICP-OES, characterized in that: The following steps are involved: (1) The plant sample is crushed and sieved, and then digested with an acidic solution. After digestion, the acid is removed to obtain the plant sample to be tested; (2) The SHDES precursor, proton donor, effervescent agent and lead complexing agent are mixed evenly, subjected to ultrasonic treatment and heating, and the aqueous phase is removed by centrifugation. The obtained organic phase is resolved with an acidic solution, and the aqueous phase is taken by centrifugation to obtain FA-SHDES-ME; (3) The plant sample to be tested in step (1) and the FA-SHDES-ME in step (2) are mixed for enrichment, and the lead content in the plant sample is determined by ICP-OES.

2. The method according to claim 1, characterized in that: The SHDES precursor includes HBA and HBD; the HBA is at least one of choline chloride, tetrabutylammonium bromide, thymol, and acetylcholine chloride; the HBD is sodium octanoate; and the mass ratio of the HBA to the HBD is 1:1-3.

3. The method according to claim 1, characterized in that: The proton donor is malonic acid; the effervescent agent is sodium bicarbonate; and the lead complexing agent is dithizone.

4. The method according to claim 2, characterized in that: The dosage of sodium octanoate is 400 mg-800 mg.

5. The method according to claim 3, characterized in that: The dosage of malonic acid is 650 mg-750 mg.

6. The method according to claim 3, characterized in that The amount of sodium bicarbonate used is 600 mg-800 mg.

7. The method according to claim 3, characterized in that The concentration of dithizone is 0.5×10 -5 mol / L–1.0×10 -5 mol / L.

8. The method according to claim 1, characterized in that The ultrasonic treatment time is 15 min-20 min.

9. The method according to claim 1, characterized in that: The volume ratio of the plant sample to be tested to FA-SHDES-ME is 1:1-10.

10. The method according to claim 1, characterized in that The plant is Pinellia ternata.

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