Method for detecting content of talcum powder in food based on graphite digestion and mass spectrometry technology

Abstract

The invention belongs to the technical field of food detection, and particularly relates to a method for detecting the content of talcum powder in food based on graphite digestion and mass spectrometry, and the detection method comprises the following steps: (1) uniformly mixing flour, weighing two parts of flour with the same mass, putting the two parts of flour into a graphite digestion instrument, and digesting to obtain a digestion solution after the digestion is finished, (2) preparing a standard solution, and drawing a standard curve; (3) respectively injecting the to-be-detected sample solution and the blank sample solution into an inductively coupled plasma mass spectrometer, determining a signal response value of the magnesium element, obtaining the concentration of the magnesium element in the sample solution according to the standard curve, and then calculating the content of the magnesium element; and (4) calculating the content of talcum powder in the flour according to a formula. The invention provides a brand new method for detecting the content of talcum powder in flour, the digestion time is short, the sample weighing amount is not limited, and the detection limit is low.

Description

Technical Field

[0001] The invention belongs to the technical field of food detection, and particularly relates to a method for detecting talcum powder content in food based on graphite digestion and mass spectrometry technology. Background Art

[0002] Talc is made by removing dirt and rocks from talc, then crushing, flotation and drying. Its main component is natural hydrated magnesium silicate, with the molecular formula of Mg3[Si4O 10 ](OH)2. According to the relevant provisions of the national standard GB 2760-2024 "National Food Safety Standard: Food Additives Usage Standard", talcum powder can be used as a food additive in the production of candy foods during the processing link, and shall not be used in the production of other foods. Long-term and large-dose use of talcum powder in the human body will cause kidney silicate stones, and people with renal insufficiency may experience dizziness, fainting, arrhythmia, and abnormal fatigue and weakness. The detection of talcum powder in food is a very important part of food safety testing.

[0003] At present, the current detection method of talc in food in my country is GB 5009.269-2016 "National Food Safety Standard for the Determination of Talc in Food". The pre-treatment operation of this method is cumbersome, time-consuming, consumes a large amount of acid, is easy to lose, and the test results are low and have large interference. The entire digestion process generally takes about 12-15 hours. During the digestion process, it is necessary to weigh the sample, add liquid, shift, and prepare utensils and reagents. Without considering overtime, it is necessary to heat up and cool down due to the restrictions on working hours, which requires at least one and a half working days (in fact, it often takes 2 days). This method is complicated and time-consuming, and requires experienced testers to perform the determination. At the same time, more strong acids are used, and safety protection is required during the operation process. The waste liquid generated will also cause an environmental burden. In addition, a series of operations for filtration between two digestions increase the chance of sample loss or contamination, which is not conducive to the high-throughput detection and supervision of talc in food. Therefore, it is very necessary to develop a simple, efficient and accurate method for detecting talc in food. Summary of the invention

[0004] The purpose of the invention is to provide a method for detecting the content of talc in food based on graphite digestion and mass spectrometry technology.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A method for detecting talc content in food based on graphite digestion and mass spectrometry technology, the detection method comprising the following steps:

[0007] (1) After the flour is mixed evenly, two portions of flour of the same mass are weighed and placed in polytetrafluoroethylene digestion tube A and polytetrafluoroethylene digestion tube B, respectively. Concentrated nitric acid and perchloric acid are added to polytetrafluoroethylene digestion tube A, and concentrated nitric acid, perchloric acid and hydrofluoric acid are added to polytetrafluoroethylene digestion tube B. The mixture is shaken slightly, and then placed in a graphite digestion instrument with a lid covered for digestion. After the digestion is completed, a digestion solution is obtained. The digestion solution is taken out and then fixed to volume. A blank solution is obtained in polytetrafluoroethylene digestion tube A, and a sample solution is obtained in polytetrafluoroethylene digestion tube B.

[0008] (2) preparing standard solutions: preparing magnesium standard solutions with concentrations of 0.0, 10, 50, 100, 150, and 200 μg / L by stepwise dilution with 2% nitric acid aqueous solution; detecting the intensity response value of magnesium element of each standard solution by inductively coupled plasma mass spectrometry, and drawing a standard curve with the intensity response value of magnesium element as the ordinate and the concentration as the abscissa;

[0009] (3) injecting the sample solution to be tested and the blank sample solution into an inductively coupled plasma mass spectrometer respectively, measuring the signal response value of the magnesium element, obtaining the concentration of the magnesium element in the sample solution according to the standard curve, and then calculating the magnesium element content;

[0010] (4) Talc content in flour w = (ρ1-ρ2)*V*5.27 / (m*1000);

[0011] Where w is the mass fraction of talc in the sample, g·kg -1 ; ρ1 is the total magnesium concentration in the sample solution, mg·L -1 ; ρ2 is the mass concentration of magnesium in the blank solution, mg·L -1 ; V is the fixed volume, mL; m is the sample mass, g; 5.27 is the conversion factor, and the relative molecular mass of talc is 379.3.

[0012] Furthermore, 4 mL of concentrated nitric acid and 1 mL of perchloric acid were added into the polytetrafluoroethylene digestion tube A for every 0.5 g of flour.

[0013] Furthermore, 4 mL of concentrated nitric acid, 1 mL of perchloric acid and 1 mL of hydrofluoric acid were added into the polytetrafluoroethylene digestion tube B for every 0.5 g of flour.

[0014] Furthermore, the digestion procedure in the graphite digester is: under the condition of a power of 600W-700W, the temperature is increased from room temperature to 120-125°C at a heating rate of 15-20°C / min, and the temperature is kept for 60-65min; then the temperature is increased to 180-185°C at a heating rate of 20-25°C / min, and the temperature is kept for 20-25min.

[0015] Furthermore, the digestion procedure in the graphite digester is: under the condition of a power of 650 W, the temperature is increased from room temperature to 120° C. at a heating rate of 17° C. / min, and kept at that temperature for 60 min; then the temperature is increased to 180° C. at a heating rate of 22° C. / min, and kept at that temperature for 20 min.

[0016] Furthermore, the working conditions of the inductively coupled plasma mass spectrometer are: cooling gas flow rate 13.0 L·min -1 ; Auxiliary gas flow rate 0.8L·min -1 , sampling cone diameter 1.0mm, intercepting cone diameter 0.4mm, scanning times 2 times, RF power 1200W, peristaltic pump speed 0.1r·s-1.

[0017] Furthermore, after the digestion in step (1) is completed, the polytetrafluoroethylene digestion tube A and the polytetrafluoroethylene digestion tube B are cooled to below 40° C., and saturated boric acid solution is added respectively, and 10.0 mL of saturated boric acid solution is added for every 0.5 g of flour. The mixture is covered and heated to 40-45° C. and maintained for 8-12 minutes to obtain digestion solutions, which are then taken out and fixed to volume.

[0018] Inductively coupled plasma mass spectrometer can tolerate a certain concentration of HF, but HF can form magnesium fluoride that is slightly soluble in nitric acid with magnesium ions, resulting in low test results. Especially in batch sample testing, it will also aggravate the corrosion of glassware such as instrument torches and nebulizers. In order to eliminate the interference of HF, the method of HClO4 fuming is generally adopted, but this method is cumbersome to operate, and the degree of fuming is not easy to grasp, and the experimental results are unstable. The present invention further uses a certain amount of saturated boric acid solution (H3BO3) as a masking agent to eliminate the interference of HF after using acid digestion. Analysis shows that boric acid will complex with HF to form fluoroboric acid.

[0019] Furthermore, the mass concentration of concentrated nitric acid is 68%, the mass concentration of perchloric acid is 70%, and the mass concentration of hydrofluoric acid is 49%.

[0020] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0021] 1. Currently, the detection of talcum powder in food mainly uses microwave digestion instrument for digestion, which has the disadvantage of limiting the sample weight. The powder sample cannot exceed 0.5g (to avoid can explosion), and pre-digestion is required, otherwise it will react violently and lose. Since flour is a powdery sample, the present invention uses a graphite digestion instrument, which does not need to limit the sample weight; and does not require pre-digestion, and directly weighs and digests the sample, which has strong adaptability.

[0022] 2. The height of the polytetrafluoroethylene digestion tube of the present invention is 10 cm, the diameter is 3 cm, and the side of the tube cover is provided with a vent hole with a diameter of 0.8 mm. The small holes on the polytetrafluoroethylene digestion tube cover of the present invention are different from the small holes on the ordinary digestion cover. By changing the position of the small holes on the tube cover and reducing the aperture, volatilization is reduced, thereby greatly improving the overall digestion rate, and improving the sensitivity and accuracy of the detection.

[0023] 3. After the digestion of the present invention is completed, saturated boric acid solution is continued to be added as a masking agent to eliminate the interference of HF, to prevent HF and magnesium ions from forming magnesium fluoride which is slightly soluble in nitric acid, which can effectively improve the recovery rate of magnesium determination, and at the same time, can also play a role in redissolution, which can effectively improve the precision and reproducibility of the test results.

[0024] 4. The digestion procedure in the graphite digestion apparatus of the present invention is compatible with the novel polytetrafluoroethylene digestion tube of the present invention. The combination of the two can achieve a better digestion effect and improve the detection limit.

[0025] 5. The present invention can improve the sample digestion effect, digestion efficiency, method detection limit and accuracy by using specific acid for digestion. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the structure of the new digestive tube and the common polytetrafluoroethylene digestion tube used in the present invention. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The raw materials used in the following examples of the present invention are all commercially available products:

[0029] Intelligent graphite digestion instrument, Guangzhou Sanyan, model LF63.

[0030] Inductively coupled plasma atomic emission spectrometer, Thermo Fisher Scientific, USA, model Xseries2.

[0031] The mass concentration of concentrated nitric acid is 68%, the mass concentration of perchloric acid is 70%, and the mass concentration of hydrofluoric acid is 49%.

[0032] Example 1

[0033] This embodiment provides a method for detecting talc content in food based on graphite digestion and mass spectrometry technology, and the detection method comprises the following steps:

[0034] (1) After the flour is mixed evenly, weigh two portions of 0.5 g of flour. After each food sample is mixed evenly, weigh two portions of 0.5 g (accurate to 0.0001 g) of sample into two 50 mL polytetrafluoroethylene digestion tubes (10 cm high, 3 cm in diameter, with a small hole of about 0.8 mm in diameter on the tube cover). Add 4 mL of nitric acid and 1 mL of perchloric acid to one tube (to determine the content of impurities magnesium other than magnesium silicate), and add 4 mL of nitric acid, 1 mL of perchloric acid, and 1 mL of hydrofluoric acid to the other tube (to determine the total magnesium content). Shake slightly, then put into the intelligent graphite digestion instrument, set the program for digestion; digestion is performed in the graphite digestion instrument The procedure is as follows: under the condition of power of 650W, the temperature is raised from room temperature to 120℃ at a heating rate of 17 / min, and kept at this temperature for 60min; then the temperature is raised to 180℃ at a heating rate of 22℃ / min, and kept at this temperature for 20min; after the digestion, the polytetrafluoroethylene digestion tube A and the polytetrafluoroethylene digestion tube B are cooled to 30℃, 10.0mL of saturated boric acid solution are added respectively, covered, and the temperature is raised to 40℃ and kept for 10min to obtain digestion solutions respectively, and the digestion solutions are taken out and fixed to 50mL respectively, and the blank solution is obtained in the polytetrafluoroethylene digestion tube A, and the sample solution is obtained in the polytetrafluoroethylene digestion tube B;

[0035] Figure 1 As shown, the polytetrafluoroethylene digestion tube used in the present invention is a new type of digestion tube. The polytetrafluoroethylene digestion tube is 10 cm high and 3 cm in diameter, and the side of the tube cover is provided with a vent hole with a diameter of 0.8 mm.

[0036] During the application of the graphite digestion method, due to the rapid volatilization of acid at high temperature, it is necessary to pay close attention to the digestion of the sample to determine whether acid supplementation is needed, thereby increasing the digestion steps and increasing the difficulty of determining the digestion endpoint. How to increase the utilization efficiency of the acid in the graphite tube and reduce the steps of acid supplementation and digestion endpoint determination is the premise for whether the graphite digestion method can be used for rapid pre-treatment of large quantities of samples. The small holes on the lid of the polytetrafluoroethylene digestion tube of the present invention are different from the small holes in the ordinary digestion lid. By changing the position of the small holes on the tube cover and reducing the aperture, volatilization is reduced, thereby greatly improving the total digestion rate. The exhaust hole of the ordinary digestion tube is 1-1.2mm and in the center of the lid. After the polytetrafluoroethylene digestion tube of the present invention is covered with a new lid, the acid in the tube will slowly volatilize through the small holes, and the digestion process does not need to open the lid frequently, thereby removing the step of acid supplementation in the middle and directly reaching the end of digestion, which is convenient and fast.

[0037] (2) Preparation of standard solution: Prepare magnesium standard solutions with concentrations of 0.0, 10, 50, 100, 150, and 200 μg / L by diluting 2% nitric acid solution in stages;

[0038] (3) using an inductively coupled plasma mass spectrometer to detect the intensity response value of the magnesium element of each standard solution, and drawing a standard curve with the intensity response value of the magnesium element as the ordinate and the concentration as the abscissa;

[0039] (4) The sample solution and the blank sample solution were injected into the inductively coupled plasma mass spectrometer to measure the signal response value of the magnesium element. The working conditions of the inductively coupled plasma mass spectrometer were: cooling gas flow rate 13.0 L·min -1 ; Auxiliary gas flow rate 0.8L·min -1 , sampling cone diameter 1.0mm, intercepting cone diameter 0.4mm, scanning times 2 times, RF power 1200W, peristaltic pump speed 0.1r·s -1 . The concentration of magnesium in the sample solution is obtained according to the standard curve, and then the magnesium content is calculated;

[0040] (5) Talc content in flour w = (ρ1-ρ2)*V*5.27 / (m*1000); where w is the mass fraction of talc in the sample, g·kg -1 ; ρ1 is the total magnesium concentration in the sample solution, mg·L -1 ; ρ2 is the mass concentration of magnesium impurities other than magnesium silicate, mg·L -1 ; V is the constant volume, mL; m is the sample mass, g; 5.27 is the conversion factor (the relative molecular mass of talc is 379.3). The technical indicators of the detection method of this embodiment are shown in Table 1.

[0041] Table 1 Technical indicators of the detection method of Example 1

[0042]

[0043] As can be seen from Table 1, the detection limit obtained in this embodiment is 0.0074 mg / kg, which meets the analysis requirements. The correlation coefficients of the linear regression equations are all greater than 0.999, indicating that the detection method has a good linear relationship.

[0044] Example 2 Element interference experiment:

[0045] Flour has high content of calcium, potassium and sodium, which are used as interference factors to test whether they will affect the detection of magnesium in the sample (flour). A gradient experiment is also conducted. If there is an impact, a graph is drawn based on its concentration and impact value to determine whether the content of potassium, calcium, sodium and other elements in the sample will affect the detection of magnesium ions and the scope and size of the impact.

[0046] The specific steps are as follows: prepare standard solutions of potassium, calcium, and sodium of different concentrations, namely 10 mg / L, 25 mg / L, and 50 mg / L.

[0047] The experiment was divided into three groups: potassium group, calcium group, and sodium group.

[0048] Potassium group experiment: After the sample is homogenized, weigh 0.5g (accurate to 0.0001g) of the sample and add 10mg / L, 25mg / L, and 50mg / L potassium standard solutions respectively. Perform the experiment according to the established method to determine the Mg content.

[0049] Calcium group experiment: After the sample is homogenized, weigh 0.5g (accurate to 0.0001g) of the sample and add 10mg / L, 25mg / L, and 50mg / L calcium standard solutions respectively. Perform the experiment according to the established method to determine the Mg content.

[0050] Sodium group experiment: After the sample is homogenized, weigh 0.5g (accurate to 0.0001g) of sample and add 10mg / L, 25mg / L, and 50mg / L sodium standard solutions respectively. Perform the experiment according to the established method to determine the Mg content.

[0051] The changes in the Mg values ​​in the samples after adding different concentrations of potassium, calcium and sodium were recorded to compare their effects on the Mg determination. The results are shown in Table 2.

[0052] Table 2 Interference test of potassium, calcium and sodium on magnesium

[0053]

[0054] The results in Table 2 show that the relative deviation of the response loudness of the magnesium element is no more than 5.0%, indicating that high content of sodium, potassium and calcium has little interference on the determination of magnesium element.

[0055] Comparative Example 1

[0056] The difference between this comparative example and Example 1 is that a conventional polytetrafluoroethylene digestion tube is used for digestion. Figure 1 The difference between the novel digestion tube of the present invention and the novel digestion tube is that the diameter of the exhaust hole is 1.2 mm and is located in the center of the lid.

[0057] The results are shown in Table 3.

[0058] Table 3 Technical indicators of the detection method of comparative example 1

[0059]

[0060] By comparing Table 1 and Table 3, it can be seen that the detection limit of the new digestion tube used in Example 1 of the present invention is lower and the precision is better.

[0061] Comparative Example 2

[0062] The difference between this comparative example and Example 1 is that after the digestion is completed, 10.0 mL of saturated boric acid solution is not added as a masking agent to eliminate the interference of HF.

[0063] The results are shown in Table 4.

[0064] Table 4 Technical indicators of the detection method of comparative example 2

[0065]

[0066] It can be seen from Table 4 that if saturated boric acid solution is not used as a masking agent, the detection limit and precision effects become worse.

[0067] Comparative Example 3

[0068] The difference between this comparative example and Example 1 is that the composition of the acid used is different: 4 mL of concentrated nitric acid and 1 mL of hydrogen peroxide are added to each 0.5 g of flour in the polytetrafluoroethylene digestion tube B. The results show that the sample effect is not good. Without the presence of perchloric acid, the nitric acid and hydrofluoric acid in the tank are easily volatilized, affecting the digestion, resulting in some samples not being completely digested, the solution being turbid, and there being more black impurities on the tube wall, indicating that the sample digestion failed.

[0069] Comparative Example 4

[0070] This comparative example uses the microwave digestion method of the national food safety standard GB 5009.269-2016 to detect talc. The microwave digestion procedure is as follows: (1) program heating to 100°C for 7 minutes and hold for 10 minutes; (2) 5 minutes to 150°C and hold for 15 minutes; (3) 3 minutes to 180°C and hold for 15 minutes. The digestion solution is measured by atomic absorption spectrometry. The standard method detection limit of talc by microwave digestion is 2000 mg / kg (2 g / kg).

[0071] The results are shown in Table 5.

[0072] Table 5 Technical indicators of microwave digestion detection method

[0073]

[0074] In summary, the detection method of the present invention has low cost, short time, can process more samples at one time, saves manpower and cost, and has important practical significance for the detection of talc in flour. The difference between the digestion method of the present invention and the microwave digestion method is shown in Table 6.

[0075] Table 6 Comparative Examples of Two Digestion Methods

[0076]

[0077]

[0078] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for detecting talc content in food based on graphite digestion and mass spectrometry technology, characterized in that: The detection method comprises the following steps: (1) After the flours are mixed evenly, two portions of flour of the same mass are weighed and placed in polytetrafluoroethylene digestion tube A and polytetrafluoroethylene digestion tube B, respectively. Concentrated nitric acid and perchloric acid are added to polytetrafluoroethylene digestion tube A, and concentrated nitric acid, perchloric acid and hydrofluoric acid are added to polytetrafluoroethylene digestion tube B. The mixture is shaken slightly and then placed in a graphite digestion instrument for digestion. After the digestion is completed, polytetrafluoroethylene digestion tube A and polytetrafluoroethylene digestion tube B are cooled to below 40° C., saturated boric acid solution is added to each tube, the tubes are covered, the temperature is raised to 40 to 45° C., and the mixture is maintained for 8 to 12 minutes to obtain digestion solutions. The digestion solutions are taken out and then fixed to volume to obtain a blank solution in polytetrafluoroethylene digestion tube A and a sample solution in polytetrafluoroethylene digestion tube B. (2) preparing standard solutions: preparing magnesium standard solutions with concentrations of 0.0 μg / L, 10 μg / L, 50 μg / L, 100 μg / L, 150 μg / L, and 200 μg / L by stepwise dilution with aqueous nitric acid solution; detecting the intensity response value of magnesium element of each standard solution by inductively coupled plasma mass spectrometry, and drawing a standard curve with the intensity response value of magnesium element as the ordinate and the concentration as the abscissa; (3) injecting the sample solution to be tested and the blank sample solution into an inductively coupled plasma mass spectrometer respectively, measuring the signal response value of the magnesium element, obtaining the concentration of the magnesium element in the sample solution according to the standard curve, and then calculating the magnesium element content; (4) Talc content in flour w = (ρ1-ρ2)*V*5.27 / (m*1000); Where w is the mass fraction of talc in the sample, g·kg -1 ; ρ1 is the total magnesium concentration in the sample solution, mg·L -1 ; ρ2 is the mass concentration of magnesium in the blank solution, mg·L -1 ; V is the fixed volume, mL; m is the sample mass, g; 5.27 is the conversion factor, and the relative molecular mass of talc is 379.

3.

2. The method for detecting talc content in food based on graphite digestion and mass spectrometry according to claim 1, characterized in that: In the step (1), 4 mL of concentrated nitric acid and 1 mL of perchloric acid were added to the polytetrafluoroethylene digestion tube A for every 0.5 g of flour.

3. The method for detecting talc content in food based on graphite digestion and mass spectrometry according to claim 1, characterized in that: In the step (1), 4 mL of concentrated nitric acid, 1 mL of perchloric acid and 1 mL of hydrofluoric acid were added to the polytetrafluoroethylene digestion tube B for every 0.5 g of flour.

4. The method for detecting talc content in food based on graphite digestion and mass spectrometry according to claim 1, characterized in that: The digestion procedure in the graphite digestion instrument in step (1) is as follows: under the condition of a power of 600W-700W, the temperature is increased from room temperature to 120-125°C at a heating rate of 15-20°C / min, and the temperature is kept for 60-65min; then the temperature is increased to 180-185°C at a heating rate of 20-25°C / min, and the temperature is kept for 20-25min.

5. The method for detecting talc content in food based on graphite digestion and mass spectrometry according to claim 1, characterized in that: The working conditions of the inductively coupled plasma mass spectrometer in step (2) are: cooling gas flow rate 13.0 L·min -1 ; Auxiliary gas flow rate 0.8L·min -1 , sampling cone diameter 1.0mm, intercepting cone diameter 0.4mm, scanning times 2 times, RF power 1200W, peristaltic pump speed 0.1r·s -1 .

6. The method for detecting talc content in food based on graphite digestion and mass spectrometry according to claim 1, characterized in that: In the step (1), 10.0 mL of saturated boric acid solution is added for every 0.5 g of flour.

7. The method for detecting talc content in food based on graphite digestion and mass spectrometry according to claim 1, characterized in that: The polytetrafluoroethylene digestion tube A and the polytetrafluoroethylene digestion tube B in step (1) are 10 cm high and 3 cm in diameter, and have a vent hole with a diameter of 0.8 mm on the side of the tube cover.

8. The method for detecting talc content in food based on graphite digestion and mass spectrometry according to claim 1, characterized in that: In the step (1), the mass concentration of concentrated nitric acid is 68%, the mass concentration of perchloric acid is 70%, and the mass concentration of hydrofluoric acid is 49%.

9. The method for detecting talc content in food based on graphite digestion and mass spectrometry according to claim 4, characterized in that: The digestion procedure in the graphite digestion instrument in step (1) is as follows: under the condition of a power of 650 W, the temperature is increased from room temperature to 120° C. at a heating rate of 17° C. / min, and the temperature is kept for 60 min; then the temperature is increased to 180° C. at a heating rate of 22° C. / min, and the temperature is kept for 20 min.

Images