CN110567775B

CN110567775B - Solid food sample pretreatment method based on ionic liquid

Info

Publication number: CN110567775B
Application number: CN201910917169.6A
Authority: CN
Inventors: 凌约涛; 王遥雪; 张霖; 潘瑞花; 王帆; 郭少飞
Original assignee: Wuhan Customs Technical Center
Current assignee: Wuhan Customs Technical Center
Priority date: 2019-09-26
Filing date: 2019-09-26
Publication date: 2022-08-12
Anticipated expiration: 2039-09-26
Also published as: CN110567775A

Abstract

The invention provides a solid food sample pretreatment method based on ionic liquid, which comprises the following steps: contacting the ionic liquid with a solid food sample to be treated in concentrated HNO ₃ Heating until the sample is completely dissolved under the condition, adding deionized water and filtering. Compared with wet digestion, the pretreatment method established by the invention can shorten the pretreatment time by 36-48 times, and reduce the acid liquor consumption by 12-20 times, thereby providing a green, safe and rapid pretreatment technology in the detection and analysis of the heavy metal ions in the food solid sample.

Description

Solid food sample pretreatment method based on ionic liquid

Technical Field

The invention relates to the field of heavy metal ion detection and analysis, in particular to a pretreatment method based on ionic liquid.

Background

Because the composition of the food sample, especially the solid food sample, is complex, the content of the heavy metal ions is low, and part of heavy metal elements also have diversity of valence states and forms, before the detection and analysis of the heavy metal ions in the food sample (especially the solid food sample), the sample needs to be subjected to proper pretreatment.

The pretreatment technology for detecting and analyzing heavy metal ions in solid food samples is an ash method, a microwave digestion method or an acid digestion method which are commonly used at present. In these methods, a strong acid strong oxidizing reagent is used to decompose a sample under high temperature and high pressure, after the test sample is dissolved, heavy metal ions are separated and concentrated by a suitable method, and finally, an instrument is used to perform quantitative detection on the heavy metal ions. The method is time-consuming and labor-consuming, needs to consume a large amount of strong acid and strong oxidizing agent, has harsh treatment conditions, generates a large amount of waste gas, brings great harm to the health of analysts, and causes certain pollution to the environment. If the treatment is not proper, safety accidents can also occur. Meanwhile, the ash method, the microwave digestion method or the acid digestion method requires special equipment, so that the cost of sample pretreatment is increased.

Therefore, the pretreatment method of the solid food sample still needs to be improved.

Disclosure of Invention

The present invention aims to solve at least one of the technical problems in the related art to some extent or to at least provide a useful commercial choice. Therefore, the invention aims to develop a novel, green, safe, simple and convenient to operate and rapid pretreatment method based on ionic liquid aiming at the detection and analysis of metal elements in solid food samples.

The invention provides a solid food sample pretreatment method based on ionic liquid. According to an embodiment of the invention, the method comprises: contacting the ionic liquid with a solid food sample to be treated in concentrated HNO ₃ Under the condition, heating until the sample is completely dissolved, adding deionized water and then filtering.

The solid food sample is quickly dissolved through the ionic liquid, the digestion process commonly adopted at present is replaced, and the problems of safety and environmental pollution existing in the pretreatment technology of detection and analysis of heavy metal ions in the solid food sample at present are fundamentally eliminated. Compared with wet digestion, the pretreatment method established by the invention can shorten the pretreatment time by 36-48 times, and reduce the acid liquor consumption by 12-20 times, thereby providing a green, safe and rapid pretreatment technology in the detection and analysis of the heavy metal ions in the food solid sample. And after the cellulose in the sample is dissolved in the ionic liquid, the deionized water is added into the ionic liquid, the cellulose can be precipitated again, and because the cellulose molecular group is too large, if the digestion solution contains the cellulose during detection by using a graphite furnace atomic absorption spectrometry, the digestion solution is difficult to completely ash. The invention precipitates the cellulose, thus avoiding the cellulose from directly entering the graphite furnace and facilitating the subsequent detection.

The term "contacting" as used herein is to be understood broadly and can be any means that enables a chemical reaction of at least two reactants, such as mixing the two reactants under appropriate conditions.

In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

The pretreatment method based on the ionic liquid provided by the embodiment of the invention can also have the following additional technical characteristics:

according to an embodiment of the invention, the ionic liquid is a hydrophilic ionic liquid. According to a specific embodiment of the present invention, the hydrophilic ionic liquid is an ionic liquid composed of imidazole cations, halogen element anions, or acetate anions. Therefore, a pretreatment scheme of the graphite furnace atomic absorption spectrometry, which is environment-friendly, economical and efficient, can be found by utilizing the good dissolving performance and the characteristics of the hydrophilic ionic liquid for cellulose.

According to an embodiment of the present invention, the hydrophilic ionic liquid is 1, 3-dibenzylimidazole acetate, 1- (2-naphthylmethyl) -3-methylimidazole acetate, 1-heptyl-3-methylimidazole acetate, 1-ethyl-3-methylimidazole acetate, at least one of 1-acetic acid benzyl-3-methylimidazolium salt, 1- (cyclohexylmethyl) -3-methylimidazolium acetate and 1-butyl-3-methylimidazolium chloride salt, preferably at least one of 1-ethyl-3-methylimidazolium acetate, 1-acetic acid benzyl-3-methylimidazolium salt and 1-butyl-3-methylimidazolium chloride salt, and most preferably 1-butyl-3-methylimidazolium chloride salt. Therefore, the sample to be analyzed can be rapidly dissolved under the condition of ensuring that the composition structure of the sample is unchanged, and the subsequent analysis and detection of heavy metal ions are facilitated.

According to an embodiment of the invention, the ratio of the amount of ionic liquid to the amount of solid food sample to be treated is 3 g: (0.2 g-0.4 g). After the volume is adjusted to 50mL, the concentration of the ionic liquid [ Bmim ] -Cl in the aqueous solution is 0.06 g/mL.

According to an embodiment of the invention, the concentrated HNO ₃ The amount of (B) was 0.5 mL.

According to an embodiment of the invention, the time of said contacting is 5 min.

According to an embodiment of the invention, the temperature of the heating is 160 ℃.

According to an embodiment of the invention, the filtration is performed with a 0.22 μm microfiltration membrane. Therefore, the purpose of removing heavy metal ion impurities in the ionic liquid can be achieved.

At present, the ionic liquid consisting of imidazole cations, halogen element anions or acetate anions can dissolve cellulose, but the dissolution mechanism is not well researched, but experiments and molecular simulation can show that when the ionic liquid dissolves cellulose, both the anions and the cations in the ionic liquid can help the cellulose to dissolve. Because the ionic liquid is used for dissolving the cellulose, the cellulose cannot be completely degraded into micromolecular organic matters, the cellulose cannot be digested, and the cellulose precipitate can be separated out into flocculent precipitate after a large amount of deionized water is added, the ionic liquid is used for dissolving a sample, then the deionized water is added for constant volume to separate out the cellulose in the solution, and then a 0.22 mu m microporous filter membrane is adopted for filtering the solution to prevent the cellulose precipitate from entering a graphite furnace, so that the time for digesting the cellulose and the lignin in a part of food solid samples by using a traditional wet method can be saved, and a large amount of strong acid is not required to be consumed for digesting the cellulose. However, the cellulose is too slowly dissolved by singly using the ionic liquid, 4 hours are needed for dissolving the dried mushroom and dried agaric samples by singly using the ionic liquid [ Bmim ] -Cl, and the solution becomes solid after the dried tea samples are dissolved by singly using the ionic liquid [ Bmim ] -Cl, so that the dried mushroom and dried agaric cannot be dissolved by adding acid liquor and deionized water.

According to the specific embodiment of the present invention, the optimized pretreatment conditions are: use ofConcentrated 0.5mL HNO ₃ 3g of Ionic liquid [ Bmim ]]-Cl dissolved 0.3g of sample for 5min at a heating temperature of 160 ℃. According to an embodiment of the invention, in an ionic liquid [ Bmim ]]After the cellulose was dissolved in-Cl, ultrapure water was added. This causes the majority of the organisms to re-precipitate. In the presence of an ionic liquid [ Bmim ]]And after the food solid sample is dissolved by the-Cl, deionized water is added to separate out and precipitate cellulose, so that the concentration of organisms in the supernatant is low, and the digestive juice can be directly analyzed by a graphite furnace atomic absorption spectrometry to determine the content of heavy metal elements contained in the digestive juice.

Based on wet digestion in GB5009.12-2017, used glassware is soaked in concentrated nitric acid for 12 hours and then washed by deionized water, so that interference of heavy metal ions in the environment is reduced as much as possible, a large amount of strong acid is needed for completely digesting a food solid sample, most of the strong acid is discharged into the environment through a ventilation pipeline, the environment and detection personnel are harmed, the consumed time is long, and the consumed time is usually 2-4 hours.

In the prior art, the pretreatment of a food solid sample in the graphite furnace atomic absorption spectrometry generally adopts wet digestion: crushing a sample, weighing 0.2-0.3 g of the crushed sample, placing the weighed sample in a digestion tube or a beaker, adding 12-20 mL of strong acid solution such as concentrated nitric acid, concentrated perchloric acid and the like, heating to 120 ℃ for 0.5-1 h, heating to 180 ℃ for 2-4 h, heating to 200-220 ℃ for digestion, heating until the digestive juice is yellowish or transparent, emitting white smoke above the solution, cooling, fixing the volume, and inspecting.

Because acid liquor such as concentrated nitric acid, concentrated perchloric acid and the like is used in the method, a violent reaction can be generated with the sample at the beginning of the reaction to wash away the cover glass, so that heavy metal elements in the sample are lost or the sample is polluted by heavy metals in the environment. When some individual samples such as mushrooms and tea leaves are digested, problems of too long digestion time, incomplete digestion and the like occur, when the samples are digested, a cover glass is covered on a beaker to prevent the acid liquor from being lost too fast due to high-temperature evaporation, a large amount of acid liquor steam and brown gas overflow from the opening of the beaker in the digestion process, and therefore the whole experiment must be carried out in a fume hood. If the temperature of the electric heating plate is set to be too high in the digestion process, the evaporation speed of the acid liquor is too high, and the sample cannot be completely digested after the concentrated nitric acid is consumed, the final digestion solution contains excessive organic matters to interfere with subsequent detection, most of the organic matters are dissolved in water, and therefore the organic matters cannot be removed through filtration. The final heavy white smoke generated in the beaker is due to the evaporation of the concentrated perchloric acid as the concentrated nitric acid is depleted. Digestion is carried out in the previous step, because the solution in the beaker is burnt out, digestion cannot be carried out continuously, if digestion is not complete, an extra quantitative acid liquor can be added into the beaker to enable the beaker to continue digestion of organic matters, but an equal amount of acid liquor must be added into a parallel sample experiment and a blank to carry out an extra acid dispelling step, otherwise perchloric acid in the acid liquor can cause interference on a graphite furnace atomic absorption spectrometry and also cause extra loss on a graphite tube. Concentrated nitric acid and concentrated perchloric acid evaporated due to high temperature in the digestion process can be discharged into the environment, corrode a ventilation pipeline and pollute the environment, and the health of laboratory personnel and personnel around the laboratory is harmed.

According to the ionic liquid-based solid food sample pretreatment method disclosed by the embodiment of the invention, at least one of the following advantages can be realized:

1. according to the pretreatment method disclosed by the embodiment of the invention, the pretreatment method is green and environment-friendly, and the purpose of pretreatment can be achieved by using few chemical reagents. The method is simple, convenient and quick (can be completed within about half an hour), compared with the wet digestion method which requires 2-4 hours, the microwave digestion method requires about 1.5-2 hours, and the efficiency is greatly improved;

2. according to the pretreatment method disclosed by the embodiment of the invention, the reaction condition is mild, the consumption of a large amount of strong acid strong oxidant reagent is avoided, harsh reaction conditions such as high temperature and high pressure are not required, the operation environment of an analyst is improved, the health and safety of the analyst can be guaranteed, and the environment is not polluted by the reaction condition;

3. according to the pretreatment method provided by the embodiment of the invention, the problems that the existing detection method is long in time consumption, the time for waiting for digestion in detection is long, and certain human resource cost is wasted are solved, but if the cellulose in a food solid sample is completely digested, the long time is inevitably spent. The invention provides a novel, simple, convenient, rapid, green and safe pretreatment method for analyzing and detecting heavy metal ions with different valence states in a sample. The method is essentially different from the application of the ionic liquid reported in the current literature in the aspect of heavy metal ion detection and analysis, no related literature report is found, and the method has original innovation.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

FIG. 1 shows a calibration curve of a Pb solution according to example 4 of the present invention;

FIG. 2 shows a standard curve for a Cd solution according to example 4 of the invention;

FIG. 3 shows a calibration curve of a Cr solution according to example 4 of the present invention.

FIG. 4 shows the effect of dissolution time on the measured value of Pb according to example 5 of the present invention;

FIG. 5 shows the effect of dissolution time on Cd measurements according to example 5 of the present invention;

FIG. 6 shows the effect of dissolution time on Cr measurements according to example 5 of the present invention.

Detailed Description

The following describes embodiments of the present invention in detail. The following examples are illustrative only and are not to be construed as limiting the invention. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

The dried mushroom, the dried agaric and the dried tea solid samples are purchased from the market, stirred for 15min by using a stirrer, screened by a 100-mesh screen, then dried for 5h in a constant-temperature oven with the temperature set to be 100 ℃, and stored in a dry place for later use.

The main reagents are as follows: concentrated nitric acid (analytically pure, 68% strength), perchloric acid (analytically pure, 70% strength), hydrochloric acid (analytically pure, 36.5% strength), a multi-element mixed standard solution (GBW08607), ammonium dihydrogen phosphate (analytically pure), and ammonium dihydrogen phosphate solution (2% strength).

Mixing standard solutions: the mixed standard solution of Pb, Cr, Cd and other elements purchased from China institute of metrology science, wherein the concentration of Pb is 1.03 mu g/g, the concentration of Cd is 0.104 mu g/g, and the concentration of Cr is 0.516 mu g/g.

Ionic liquid (1-butyl-3-methylimidazolium chloride, [ Bmim ] -C1): CAS: 79917-90-1, obtained from commercial sources, with a concentration of 99.9%.

Main experimental apparatus and equipment: an atomic absorption spectrophotometer (AA280Z), a chromium hollow cathode lamp, a lead hollow cathode lamp, a cadmium hollow cathode lamp, a 1.5mL sample cup, and a pyrolytic graphite tube, all produced by Agilent, USA; electronic balance (mettlerlitolo (shanghai) ltd), muffle furnace FO610C (yamatuo, japan), vacuum drying oven (mei-meltt (shanghai) trade ltd).

The initial graphite furnace temperature-rising program setting conditions for detecting the Pb, Cd and Cr elements refer to the current national standard: GB5009.12-2017, GB5009.15-2014 and GB 5009.123-2014.

Pb element measurement conditions: measuring wavelength: 283.3nm, lamp current: 6.0mA, slit 0.5nm, background subtraction mode: zeeman background, the sample size was 10. mu.L, the sample size of the matrix modifier was 10. mu.L, the matrix modifier was a solution of ammonium dihydrogen phosphate (concentration: 2% by mass), the data were recorded using the peak heights, and the temperature-raising program for the graphite furnace is shown in Table 1.

TABLE 1 graphite furnace temperature-raising procedure for Pb determination

Determination conditions of Cd element: measuring wavelength: 228.8nm, lamp current: 7.0mA, slit 0.2nm, background subtraction mode: zeeman background, sample size 10. mu.L, matrix modifier 10. mu.L, and ammonium dihydrogen phosphate solution (concentration 2 mass%), and the peak height data were recorded, and the temperature program of the graphite furnace is shown in Table 2.

TABLE 2 graphite furnace temperature program for Cd determination

Cr element measurement conditions: measuring wavelength: 357.9nm, lamp current: 7.0mA, slit 0.2nm, background subtraction mode: zeeman background, sample size 10. mu.L, matrix modifier 10. mu.L, and ammonium dihydrogen phosphate solution (concentration 2 mass%) as matrix modifier, and the peak height data are recorded, and the temperature program of graphite furnace is shown in Table 3.

TABLE 3 graphite furnace temperature program for Cr determination

EXAMPLE 1 preparation of solutions

Mixing standard stock solutions: 2mL of the multi-element mixed standard solution (GBW 08607: wherein the Pb concentration is 1.03. mu.g/g, the Cd concentration is 0.104. mu.g/g, and the Cr concentration is 0.516. mu.g/g) was removed. Dissolving in 25mL deionized water, shaking and shaking to obtain a mixed standard stock solution with Pb concentration of 82.4 mug/L, Cd concentration of 8.32 mug/L and Cr concentration of 41.28 mug/L.

Example 2 sample pretreatment with ionic liquid and nitric acid

HNO ₃ The method is a solvent commonly used in sample digestion, 14mL of concentrated nitric acid and 1mL of perchloric acid are generally required to be used for wet digestion of a solid food sample, the temperature is between 200 and 300 ℃, and most of acid liquor enters a ventilation pipeline under a high-temperature condition and is discharged into the environment. The sample selected in this example was dry Auricularia, concentrated HNO ₃ The dosage is 0.5 mL. The applicant has found through experiments that heating temperature higher than 200 ℃ can cause the sample to be in the ionic liquid [ Bmim ]]The solution of-Cl is carbonized, so the heating temperature selected in this example is 170 ℃, the reaction is carried out until no solid particles exist in the solution, the solution is in a light-colored and transparent state, namely, the solution is considered to be completely dissolved, and the dissolution condition is shown in Table 4.

TABLE 4 dissolution time of solid samples of food

As can be seen from Table 4, the solution for dissolving the tea samples was completely dissolved in 5min, and the solution for dissolving the Auricularia and Lentinus Edodes samples was completely dissolved in 1min, indicating that concentrated HNO was used ₃ Assisted dissolution to give concentrated HClO ₄ The effect of assisting dissolution is also better. And adding deionized water after the sample is completely dissolved to separate out and settle the cellulose, wherein the natural settling time of the cellulose is 3-4 h.

Example 3 pretreatment of food solid samples based on ionic liquids

Accurately weighing 3g of ionic liquid [ Bmim ]]-Cl was placed in a beaker and the beaker was heated to 90 ℃ to bring the ionic liquid [ Bmim [ ]]Melting the-Cl crystal, taking down and cooling after the-Cl crystal is completely melted, accurately weighing 0.2g of sample powder into a beaker, uniformly dispersing the sample in the liquid surface, and adding 0.5mL of concentrated HNO ₃ Heating to 160 deg.C, and dissolving for 5 min. And adding deionized water after the cellulose is dissolved to precipitate cellulose, keeping the volume constant to 50mL, taking part of supernatant after the precipitated cellulose naturally settles, and detecting the supernatant by using a graphite furnace atomic absorption spectrometry, wherein the result is shown in Table 5.

TABLE 5 samples of analytical results after pretreatment

Example 4 Standard Curve was prepared

Transferring a proper amount of mixed standard stock solution (GBW 08607: wherein the Pb concentration is 1.03 mug/g, the Cd concentration is 0.104 mug/g and the Cr concentration is 0.516 mug/g) into a volumetric flask, and fixing the volume to the scale to prepare a series of mixed standard solutions. The series of mixed standard solutions were used, initial graphite furnace temperature program conditions were set with reference to the current national standards, and instrumental automatic standard curve measurements were performed, and the results obtained are shown in tables 6, 7, and 8.

TABLE 6 Absorbance of Pb Standard solutions of different concentrations

TABLE 7 Absorbance of Cd Standard solutions of different concentrations

TABLE 8 absorbance of Cr standard solutions of different concentrations

Standard curves of three elements of Pb, Cd and Cr are plotted from tables 6 to 8 and shown in FIG. 1, FIG. 2 and FIG. 3. Therefore, the following steps are carried out: the standard curve for Pb solution is abs (Pb) 0.0087 xc (μ g/L) +0.0147, with a correlation of 0.997; the standard curve for Cd solution is abs (Cd) ═ 0.0292 xc (μ g/L) +0.0087, with a correlation of 0.999; the standard curve of the Cr solution is abs (Cr) 0.0035 × C (μ g/L) +0.0452, and the correlation is 0.999. The standard curves and the correlation degree thereof can prove that the instrument has good linear correlation and high sensitivity when detecting the Pb, Cd and Cr heavy metal elements.

Example 5 Effect of dissolution time during pretreatment

Due to the added concentrated HNO ₃ Too much results in too much decomposition of the sample into small organic molecules, so too much concentrated HNO ₃ And too long heating time will have negative impact on the experiment, this example only discusses using 0.5mL concentrated HNO ₃ The influence of the time dissolution time on the measured value, according to the dissolution situation of the embodiment 2, the dry agaric which is difficult to dissolve is selected as the experimental object, the time gradient is set to be 0.5min to 10min, the detected concentration of the Pb element is shown in the attached drawing 4, the detected concentration of the Cd element is shown in the attached drawing 5, and the detected concentration of the Cr element is shown in the attached drawing 6.

As can be seen from fig. 4 to 6: when concentrated HNO ₃ When the dosage is 0.5mL, the heating time is more than 4min, and the digestion phase with the wet method can be obtainedAccording to the measured values of Pb and Cr elements, the measured value of Cd element which is consistent with wet digestion can be obtained by heating for more than 5min, and in an actual experiment in which the heating time is within 4min, residual undissolved sample particles still exist in the solution, so that the situation that the sample is not completely dissolved when the heating time is within 4min can be known, and the measured value is low. Therefore, this example finally selects HNO ₃ The dosage of (A) is 0.5mL, and the dissolving time is 5 min.

Comparative example 1 Wet digestion treatment of food solid sample

Mixing concentrated nitric acid (400mL) and concentrated nitric acid (50mL) to obtain HNO ₃ -HClO ₄ And (4) mixing acid. And (3) repeatedly cleaning the stirrer by using deionized water, placing the stirrer in a constant-temperature oven for drying, stirring the dried mushroom sample for 10min, pouring out the sample, stirring for 10min if larger particles exist, stirring until the sample is stirred into powder, and sieving by using a 100-mesh sieve for later use. Weighing three parts of dried mushroom sample powder of 0.2-0.3 g into a beaker, and simultaneously taking one beaker for a blank experiment. Adding HNO into each sample at room temperature ₃ -HClO ₄ And (3) mixed acid (15mL), wherein 5mL of mixed acid needs to be stopped when the dried mushroom powder reacts violently with the mixed acid, and 10mL of mixed acid is added after the dried mushroom powder does not react any more. Uniformly placing a beaker on an electric heating plate, covering the beaker with a circular cover glass, adjusting the temperature of the electric heating plate to 220 ℃, heating for 3h, adjusting the temperature of the electric heating plate to 250 ℃, heating until strong white smoke appears in the beaker (generally, 1h is needed in the step), continuing the next step if the digestive juice at the bottom is transparent and colorless, adding 2mL of nitric acid into each sample if the digestive juice is yellow liquid, continuing digestion, observing the color of the liquid after the white smoke appears again until the digestive juice is transparent and colorless. The beaker was removed, after it had cooled, the cover glass was rinsed with 5mL of deionized water and the rinse was transferred to the beaker (reducing the loss of heavy metals from the sample at this step). And removing the cover glass, placing the beaker on an electric hot plate, heating until 1-2 mL of liquid remains, taking the beaker off, cooling, pouring the solution into a 25mL colorimetric tube, repeatedly washing the beaker by using deionized water, and transferring the washing solution into the same colorimetric tube. Finally, deionized water is used for fixing the volume to 10mL of scale marks, and graphite furnace atomic absorption spectroscopy is carried out on the solution after oscillation is carried out by using an oscillatorThe heavy metal content in the sample is shown in table 9.

The procedure of the wet digestion experiment on the dry agaric sample was the same as that described above, and the dry agaric sample was heated on a hot plate at 220 ℃ for 2 hours and at 250 ℃ for 1.5 hours, and the heavy metal content in the sample is shown in table 9.

The procedure of the wet digestion experiment on the dry tea samples was the same as above, heating was first carried out on a hot plate at 220 ℃ for 4h and at 250 ℃ for 2.5h, and the heavy metal content in the samples is shown in table 9.

TABLE 9 concentrations of Cd, Pb and Cr in solid samples of food products

According to the method, the total time of the existing wet digestion is about 3-4 h, and a large amount of acid liquor is consumed. And the content of Cd element in the dried mushrooms is higher and the measured value is unstable. Only a small part of the acid liquor is used for digesting the sample, and most of the acid liquor is vaporized at high temperature and is discharged into the environment through a ventilation pipeline of the test bed, so that negative effects are caused on the natural environment and the laboratory environment.

Comparative example 2 treatment of food solid sample directly with ionic liquid

Accurately weighing 3g of ionic liquid [ Bmim ] -Cl, placing the ionic liquid [ Bmim ] -Cl into a beaker, heating the beaker to 90 ℃ to melt the crystals of the ionic liquid [ Bmim ] -Cl, taking down and cooling the sample after the ionic liquid [ Bmim ] -Cl is completely melted, accurately weighing 0.2g of sample powder into the beaker, uniformly dispersing the sample on the liquid surface, heating the sample to 160 ℃, adding deionized water after the sample is dissolved to precipitate out cellulose, fixing the volume to 50mL, taking part of supernatant liquid after the precipitated cellulose naturally settles out, and detecting the supernatant liquid by using a graphite furnace atomic absorption spectrometry.

The applicant of the patent finds that when the ionic liquid [ Bmim ] -Cl is used for directly dissolving a sample, no other chemical reagent is added, 4.5 hours are needed for completely dissolving the shiitake mushrooms when the temperature of an electric hot plate is set to be 160 ℃, the solution is brown after the shiitake mushrooms are completely dissolved, and the deionized water is added for precipitating and separating out the cellulose after the deionized water is shaken; when the temperature of an electric heating plate is set to be 160 ℃, the agaric is completely dissolved for 3 hours, the solution is light yellow after the agaric is completely dissolved, and the cellulose can be directly precipitated and separated out after deionized water is added; when the temperature of the electric heating plate is set to 170 ℃, the tea leaves are completely dissolved for 6 hours, the solution is black after the tea leaves are completely dissolved, and the cellulose cannot be precipitated after deionized water is added.

Thus, it can be seen that: the time for directly using the ionic liquid [ Bmim ] -Cl to dissolve the sample is too long, and the ionic liquid [ Bmim ] -Cl cannot separate out cellulose when deionized water is added after part of the food solid sample is dissolved.

Comparative example 3 treatment of a sample of food solids with an ionic liquid and HCl

The acidity of the solution was greatly enhanced by adding a small amount of concentrated HCl before dissolving the sample with the ionic liquid [ Bmim ] -Cl, the dissolution is shown in Table 10.

TABLE 10 dissolution time of solid samples of food

Experiments show that the dissolution time for dissolving the dry mushroom sample is almost unchanged after 0.5mL, 1mL and 1.5mL of concentrated hydrochloric acid are added, the dissolution time for dissolving the dry agaric is increased by 2h, and the dry tea leaves are not dissolved any more, which is presumed to be due to the following reasons: since the degree of acidity is less helpful for dissolving a solid food sample, and a small amount of moisture is brought in while adding concentrated hydrochloric acid, which results in the original ionic liquid [ Bmim ] -Cl having reduced solubility in the sample, concentrated HCl is not suitable as a reagent for assisting the dissolution of the sample.

Comparative example 4 Using an Ionic liquid and HClO ₄ Treating solid food samples

Since perchloric acid has a very strong oxidizing property, perchloric acid is preferably selected for the test when the improvement of solubility by oxidizing property is investigated. When only 0.5mL of perchloric acid is added, three food solid samples of the agaric, the tea and the mushroom are rapidly dissolved in the ionic liquid [ Bmim ] -Cl: completely dissolving Auricularia and Lentinus Edodes until no solid matter exists in the solution, and no large amount of bubbles are generated, and the time is 2 min; completely dissolving tea leaves until no solid matter exists in the solution, no large amount of bubbles are generated, and 3.5min is needed. When the heating time is prolonged to more than 1h, the solution changes from translucent to black and explosion occurs.

The heavy metal element analysis is carried out on the sample by using a graphite furnace atomic absorption spectrometry, and the detection results of Pb and Cr elements are found to be interfered if the dissolving time exceeds 10min, and a matrix modifier HNO is added ₃ The dosage of the organic acid can not eliminate interference, and supposedly, because the heating time is too long, perchloric acid oxidizes and decomposes part of cellulose into water-soluble micromolecular organic matters, so that the part of organic matters can not be precipitated after deionized water is added, and the subsequent detection is interfered; or the chlorine ions remained after the perchloric acid is reacted interfere the detection, and the perchloric acid has larger damage to the graphite tube.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Moreover, various embodiments or examples and features of various embodiments or examples described in this specification can be combined and combined by one skilled in the art without being mutually inconsistent.

Although embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are exemplary and not to be construed as limiting the present invention, and that changes, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims

1. A solid food sample pretreatment method based on ionic liquid is characterized in that:

accurately weighing 3g of 1-butyl-3-methylimidazolium chloride, placing the 1-butyl-3-methylimidazolium chloride in a beaker, heating the beaker to 90 ℃ to melt 1-butyl-3-methylimidazolium chloride crystals, taking down and cooling the beaker after the crystals are completely melted into hydrophilic ionic liquid, accurately weighing 0.2g of solid food sample powder in the beaker, uniformly dispersing the solid food sample on the liquid surface, adding 0.5mL of concentrated HNO ₃ Heating to 160 ℃, dissolving for 5min, adding deionized water after dissolving, filtering to precipitate cellulose, fixing the volume to 50mL, and taking part of supernatant after naturally settling the precipitated cellulose;

the filtration is carried out using a 0.22 μm microporous membrane.