A test sample for determining lead and cadmium content in table salt and a preparation method thereof

Abstract

The invention belongs to the field of food detection technology, and discloses a preparation method for a test sample for measuring the content of lead and cadmium in table salt, comprising the steps of: adding a digestion solution to a table salt sample to be measured to digest and obtain a digestion solution; adding a magnesium chloride solution to the digestion solution and mixing evenly, adjusting the pH value of the solution to 7-8, and then adding tetramethylammonium hydroxide to obtain a precipitate; adding a nitric acid solution to the precipitate and dissolving it to obtain a test sample to be measured. The test sample for measuring the content of lead and cadmium in table salt can effectively avoid the influence of sodium ions on the determination of lead and cadmium content, reduce background interference, and improve the stability and accuracy of the lead and cadmium determination results.

Description

Technical Field

[0001] The invention belongs to the technical field of food detection, and particularly relates to a test sample for determining the lead and cadmium contents in table salt and a preparation method thereof. Background Art

[0002] Table salt refers to processed edible salt primarily composed of sodium chloride, obtained from seawater, underground rock (mineral) salt deposits, or natural brine (salty) water. Low-sodium salt is excluded. Table salt is primarily composed of sodium chloride (NaCl), along with small amounts of water and impurities such as iron, phosphorus, and iodine. Table salt is a colorless, transparent cubic crystal with a melting point of 801°C, a boiling point of 1413°C, and a relative density of 2.165. Table salt has a salty taste and is easily deliquescent when impurities are present. It is soluble in water or glycerin, slightly soluble in ethanol, insoluble in concentrated hydrochloric acid, and its aqueous solution is neutral. Its solubility in water increases slightly with increasing temperature. Sodium chloride exists in large quantities in seawater and natural salt lakes. It can be used to produce chlorine, hydrogen, hydrochloric acid, sodium hydroxide, chlorate, hypochlorite, bleaching powder and metallic sodium, etc. It is an important chemical raw material. It can be used for food seasoning and pickling fish, meat and vegetables, as well as for salting out soap and tanning leather. Highly refined sodium chloride can be used to make physiological saline solution for clinical treatment and physiological experiments, such as sodium loss, water loss, blood loss, etc.

[0003] Currently, the determination of lead in table salt is generally performed using the salt industry general test method GB / T13025.9, or using the graphite furnace atomic absorption spectrometry method specified in the food safety standard GB 5009.12. Cadmium in table salt is generally determined using the food safety standard GB 5009.42 Salt Indicators, or using the graphite furnace atomic absorption spectrometry method specified in the food safety standard GB 5009.15. In these determination methods, because table salt contains a high concentration of sodium ions, while the concentrations of lead and cadmium in table salt are low, the presence of sodium ions creates a strong background interference in the measurement of lead and cadmium, resulting in poor stability and low accuracy in the test results for lead and cadmium. Therefore, existing methods for determining the content of lead and cadmium in table salt do not meet the requirements for lead and cadmium detection accuracy during the detection process. Summary of the Invention

[0004] The purpose of the present invention is to provide a test sample for determining the content of lead and cadmium in table salt and a preparation method thereof, as well as a method for determining the content of lead and cadmium in table salt, which can accurately determine the content of lead and cadmium in table salt.

[0005] The above-mentioned objectives are achieved by the following technical solutions.

[0006] In a first aspect, the present invention provides a method for preparing a sample for determining the content of lead and cadmium in table salt, comprising the following steps:

[0007] Adding a digestion solution to the salt sample to be tested to digest the sample and obtain a digestion solution;

[0008] Add magnesium chloride solution to the digestion solution and mix well. After adjusting the pH value of the solution to 7-8, add tetramethylammonium hydroxide to obtain a precipitate.

[0009] Add nitric acid solution to the precipitate and dissolve it to obtain the test sample.

[0010] In some embodiments, when the amount of the salt sample to be tested is 1.5 mg to 2.5 mg, the concentration of the added magnesium chloride solution is 90 g / L to 110 g / L, and the amount added is 1 mL to 2 mL.

[0011] In some embodiments, when the amount of the salt sample to be tested is 1.8 mg to 2.2 mg, the concentration of the added magnesium chloride solution is 98 g / L to 102 g / L, and the amount added is 1 mL to 1.5 mL.

[0012] In some embodiments, the concentration of the added tetramethylammonium hydroxide solution is 23% to 27% (v / v), and the amount added is 1.5 mL to 3 mL; preferably, the amount of the added tetramethylammonium hydroxide solution is 1.5 mL to 2 mL.

[0013] In some embodiments, the volume ratio of the added magnesium chloride solution to the tetramethylammonium hydroxide solution is 1:1-2; preferably, the volume ratio of the added magnesium chloride solution to the tetramethylammonium hydroxide solution is 1:1-1.2.

[0014] In some embodiments, tetramethylammonium hydroxide solution and / or sodium hydroxide solution are used to adjust the pH value of the solution; preferably, tetramethylammonium hydroxide solution is used to adjust the pH value of the solution.

[0015] In some embodiments, the step of adjusting the pH value of the solution to 7-8 comprises the following steps:

[0016] While shaking the solution, 23-25% (v / v) tetramethylammonium hydroxide solution and / or 190-210 g / L sodium hydroxide solution are added dropwise to adjust the pH value of the solution; preferably, the pH value adjusting agent added dropwise is 23-25% (v / v) tetramethylammonium hydroxide solution.

[0017] In some embodiments, the digestion solution is a 4-6% (v / v) nitric acid solution, and the amount added is 8 mL to 12 mL.

[0018] In some embodiments, the step of adding a digestion solution to the salt sample to be tested for digestion to obtain a digestion solution comprises the following steps:

[0019] After adding the digestion solution to the salt sample to be tested, heating and digesting at 175° C. to 185° C. for 18 min to 22 min, and cooling to obtain the digestion solution.

[0020] The second aspect of the present invention provides a test sample prepared by the preparation method described above for use in determining the content of lead and cadmium in table salt.

[0021] A third aspect of the present invention provides a method for determining the content of lead and cadmium in table salt, comprising the following steps:

[0022] The lead and cadmium contents in the samples were determined by inductively coupled plasma mass spectrometry.

[0023] In the preparation of a test sample for determining the content of lead and cadmium in table salt of the present invention, a table salt sample is digested and added to a magnesium chloride solution for mixing, the pH value of the solution is adjusted, and tetramethylammonium hydroxide is added to co-precipitate lead, cadmium and magnesium ions in the solution. The magnesium ions can wrap and adsorb lead ions and cadmium ions to enrich the concentration of lead ions and cadmium ions in the precipitate, and the precipitate of lead, cadmium and magnesium ions can be stably present in the solution. The precipitate can be precipitated to be separated from sodium ions in the solution, and the influence of sodium ions on the determination of lead and cadmium content can be effectively avoided, background interference can be reduced, and the stability and accuracy of the lead and cadmium determination results can be improved.

[0024] Furthermore, by adding specific amounts of magnesium chloride and tetramethylammonium hydroxide, and adjusting the pH value of the solution using a specific pH adjuster, the amount of precipitate formed during co-precipitation can be increased, the effect of precipitating lead and cadmium can be better, and the background interference can be further reduced, so that when the lead and cadmium elements are finally tested, the stability and accuracy of the lead and cadmium determination results can be improved. DETAILED DESCRIPTION

[0025] To facilitate understanding of the present invention, the present invention will be described more fully below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the present disclosure more thorough and comprehensive.

[0026] In the following examples, the experimental methods without specific conditions are generally carried out under conventional conditions or conditions recommended by the manufacturers. The various commonly used chemical reagents used in the examples are all commercially available products.

[0027] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as those belonging to the art and

[0028] The terms "and / or" and "and / or" used in the present invention are intended to be used only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" as used in the present invention includes any and all combinations of one or more of the related listed items.

[0029] In the present invention, a method for preparing a sample for determining the content of lead and cadmium in table salt is provided, comprising the following steps:

[0030] Adding a digestion solution to the salt sample to be tested to digest the sample and obtain a digestion solution;

[0031] Add magnesium chloride solution to the digestion solution and mix well. After adjusting the pH value of the solution to 7-8, add tetramethylammonium hydroxide to obtain a precipitate.

[0032] Add nitric acid solution to the precipitate and dissolve it to obtain the test sample.

[0033] According to the above, by digesting the salt sample and adding water and magnesium chloride solution to mix, adjusting the pH value of the solution, and adding tetramethylammonium hydroxide to co-precipitate the lead, cadmium and magnesium ions in the solution, the magnesium ions can wrap and adsorb the lead ions and cadmium ions to enrich the concentration of lead ions and cadmium ions in the precipitate, and make the precipitate of lead, cadmium and magnesium ions stably exist in the solution, which can effectively avoid the influence of sodium ions on the determination of lead and cadmium content, reduce background interference, and improve the stability and accuracy of the lead and cadmium determination results.

[0034] The present invention is described in detail below with reference to specific embodiments.

[0035] Example 1

[0036] This embodiment provides a method for determining the content of lead and cadmium in table salt, comprising the following steps:

[0037] Prepare 4 conical flasks numbered A1-1, A1-2, A1-J1, and A1-J2, weigh 2.0 g (accurate to 0.1 mg) of salt sample into each of the 4 A1 flasks, then add 1.00 mL of a mixed standard solution of 250 μg / L lead and 50 μg / L cadmium into A1-J1 and A1-J2, add 1.00 mL of first-grade water into A1-1 and A1-2, and then add 10 mL of 5% (v / v) ethanol into each conical flask containing the sample. ) nitric acid solution, heat on a 180℃ hot plate for 20 minutes, remove and cool, add 5ml of water, adjust the pH to 7.5 with 25% (v / v) tetramethylammonium hydroxide solution, add 1.5ml of magnesium chloride (100g / L), and then add 1.5ml of 25% (v / v) tetramethylammonium hydroxide solution for co-precipitation, transfer the precipitated solution to a 50ml centrifuge tube, centrifuge at 5000r / min for 5min, discard the upper supernatant, add 5ml of 65% (v / v) nitric acid solution to dissolve the precipitate, and transfer it to a conical flask, place on a hot plate and heat until completely dissolved. After complete dissolution, remove and cool, make up to the volume in a 25ml volumetric flask, and at the same time make a reagent blank and shake well for testing.

[0038] (2) Use a 10 mL pipette to accurately transfer the commercially available lead standard solution (1000 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 100 mg / L lead standard stock solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 10 mg / L lead standard intermediate solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L lead standard intermediate solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L lead standard intermediate solution. The standard stock solution (1 mg / L) is placed in a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain a 0.1 mg / L lead standard intermediate solution; 0.0 mL, 1.0 mL, 5.0 mL, 10.0 mL, and 20.0 mL of the 0.1 mg / L lead standard intermediate solution are respectively pipetted into five 100 mL volumetric flasks, and 5.0 mL of the 1 mg / L lead standard intermediate solution is pipetted into a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain 0.0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, and 50 μg / L standard working curve solutions, which are then shaken to obtain the lead standard working curve solution to be tested.

[0039] Accurately pipette the commercially available cadmium standard solution (1000 mg / L) into a 100 mL volumetric flask with a 10 mL pipette, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 100 mg / L cadmium standard stock solution; accurately pipette the cadmium standard stock solution (100 mg / L) into a 100 mL volumetric flask with a 10 mL pipette, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 10 mg / L cadmium standard intermediate solution; accurately pipette the cadmium standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution; accurately pipette the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution; accurately pipette the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution. A quasi-stock solution (1 mg / L) is placed in a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain a 0.1 mg / L cadmium standard intermediate solution; 0.0 mL, 1.0 mL, 5.0 mL, 10.0 mL, and 20.0 mL of the 0.1 mg / L lead standard intermediate solution are respectively pipetted into six 100 mL volumetric flasks, and 5.0 mL of the 1 mg / L cadmium standard intermediate solution is pipetted into a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain standard working curve solutions of 0.0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, and 50 μg / L, and shaken to obtain a cadmium standard working curve solution to be tested.

[0040] (3) Use an Agilent inductively coupled plasma mass spectrometer (Model 7700), turn on the instrument and related auxiliary equipment and computer, and preheat the instrument for 20 minutes.

[0041] (4) Set the instrument test parameters: RF power / 1.55kW, plasma argon gas flow rate / 15.0L.min-1, auxiliary gas flow rate / 1.00L.min-1, pump speed / 15rpm, spray chamber temperature 2℃, spray gas flow rate / 0.70L.min-1, stabilization time / 25s, scanning mode is peak jump, and the number of repetitions is 3 times. After meeting the requirements, complete the test of the lead and cadmium element standard working curves first, and then analyze the reagent blank solution and sample solution, numbered A1-1, A1-2, A1-J1, A1-J2; the lead ion concentrations are 4.4761μg / L, 4.0822μg / L, 13.0824μg / L; 12.8513μg / L respectively;

[0042] The numbers are A1-1, A1-2, A1-J1, A1-J2; the cadmium ion concentrations are 1.0761μg / L, 1.1122μg / L, 2.9951μg / L, and 2.9382μg / L respectively.

[0043] (5) The lead ion contents in samples numbered A1-1, A1-2, A1-J1, and A1-J2 were calculated to be 0.05584 mg / kg, 0.05077 mg / kg, 0.1628 mg / kg, and 0.1602 mg / kg, respectively; the spiked recoveries were 88.0% and 85.7%, respectively.

[0044] By calculation, the cadmium ion contents in samples numbered A1-1, A1-2, A1-J1, and A1-J2 were 0.01342 mg / kg, 0.01383 mg / kg, 0.03728 mg / kg, and 0.03651 mg / kg, respectively; the spiked recoveries were 95.1% and 92.3%.

[0045] Example 2

[0046] This embodiment provides a method for determining the content of lead and cadmium in table salt, comprising the following steps:

[0047] Prepare 4 polytetrafluoroethylene beakers numbered B1-1, B1-2, B1-J1, and B1-J2, weigh 2.0 g (accurate to 0.1 mg) of salt sample into each of the 4 B1 beakers, then add 1.00 mL of a mixed standard solution of 250 μg / L lead and 50 μg / L cadmium to B1-J1 and B1-J2, respectively, add 1.00 mL of first-grade water to B1-1 and B1-2, and then add 10 mL of 5% (v / v) nitric acid solution to each polytetrafluoroethylene beaker containing the sample, heat on a 180°C hot plate for 20 min, remove and cool, add 5 mL of water, adjust the pH to 7.5 with sodium hydroxide solution (200 g / L), add 1.5 mL of magnesium chloride (100 g / L), and then add 1.5 mL of Co-precipitate with 25% (v / v) tetramethylammonium hydroxide solution, transfer the precipitated solution to a 50ml centrifuge tube, centrifuge at 5000r / min for 5min, discard the upper supernatant, add 5ml of 65% (v / v) nitric acid solution to dissolve the precipitate, and transfer it to a conical flask, place it on a hot plate and heat until completely dissolved. After complete dissolution, remove it and let it cool, dilute to a 25ml volumetric flask, and at the same time make a reagent blank and shake it for testing.

[0048] (2) Use a 10 mL pipette to accurately transfer the commercially available lead standard solution (1000 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 100 mg / L lead standard stock solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 10 mg / L lead standard intermediate solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L lead standard intermediate solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L lead standard intermediate solution. The standard stock solution (1 mg / L) is placed in a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain a 0.1 mg / L lead standard intermediate solution; 0.0 mL, 1.0 mL, 5.0 mL, 10.0 mL, and 20.0 mL of the 0.1 mg / L lead standard intermediate solution are respectively pipetted into five 100 mL volumetric flasks, and 5.0 mL of the 1 mg / L lead standard intermediate solution is pipetted into a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain 0.0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, and 50 μg / L standard working curve solutions, which are then shaken to obtain the lead standard working curve solution to be tested.

[0049] Accurately pipette the commercially available cadmium standard solution (1000 mg / L) into a 100 mL volumetric flask with a 10 mL pipette, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 100 mg / L cadmium standard stock solution; accurately pipette the cadmium standard stock solution (100 mg / L) into a 100 mL volumetric flask with a 10 mL pipette, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 10 mg / L cadmium standard intermediate solution; accurately pipette the cadmium standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution; accurately pipette the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution; accurately pipette the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution. A quasi-stock solution (1 mg / L) is placed in a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain a 0.1 mg / L cadmium standard intermediate solution; 0.0 mL, 1.0 mL, 5.0 mL, 10.0 mL, and 20.0 mL of the 0.1 mg / L lead standard intermediate solution are respectively pipetted into six 100 mL volumetric flasks, and 5.0 mL of the 1 mg / L cadmium standard intermediate solution is pipetted into a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain standard working curve solutions of 0.0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, and 50 μg / L, and shaken to obtain a cadmium standard working curve solution to be tested.

[0050] (3) Use an Agilent inductively coupled plasma mass spectrometer (Model 7700), turn on the instrument and related auxiliary equipment and computer, and preheat the instrument for 20 minutes.

[0051] (4) Set the instrument test parameters: RF power / 1.55kW, plasma argon gas flow rate / 15.0L.min-1, auxiliary gas flow rate / 1.00L.min-1, pump speed / 15rpm, spray chamber temperature 2℃, spray gas flow rate / 0.70L.min-1, stabilization time / 25s, scanning mode is peak jump, and the number of repetitions is 3 times. After meeting the requirements, complete the test of the lead and cadmium element standard working curves first, and then analyze the reagent blank solution and sample solution, numbered B1-1, B1-2, B1-J1, B1-J2; the lead ion concentrations are 3.6248μg / L, 3.3829μg / L, 11.6824μg / L; 11.5113μg / L respectively;

[0052] The numbers are B1-1, B1-2, B1-J1, and B1-J2; the cadmium ion concentrations are 0.9533μg / L, 0.9924μg / L, 2.8071μg / L, and 2.7888μg / L respectively.

[0053] (5) The lead ion contents in samples numbered B1-1, B1-2, B1-J1, and B1-J2 were calculated to be 0.04521 mg / kg, 0.04208 mg / kg, 0.1453 mg / kg, and 0.1433 mg / kg, respectively; the spiked recoveries were 81.8% and 80.1%, respectively.

[0054] By calculation, the cadmium ion contents in samples numbered B1-1, B1-2, B1-J1, and B1-J2 were 0.01189 mg / kg, 0.01234 mg / kg, 0.03491 mg / kg, and 0.03472 mg / kg, respectively; the spiked recoveries were 91.7% and 90.8%.

[0055] Example 3

[0056] This embodiment provides a method for determining the content of lead and cadmium in table salt, comprising the following steps:

[0057] Prepare four 150ml conical flasks numbered C1-1, C1-2, C1-J1, and C1-J2, and weigh 2.0g (accurate to 0.1mg) of salt sample into each of the four C1 flasks. Then, add 1.00mL of a mixed standard solution of 250μg / L lead and 50μg / L cadmium into C1-J1 and C1-J2, respectively. Add 1.00mL of first-grade water into C1-1 and C1-2, and then add 10mL of water into each conical flask containing the sample. L of 5% (v / v) nitric acid solution, place it on a 180℃ hot plate and heat it for 20 minutes, then remove it and let it cool, add 5ml of water, adjust the pH to 7.5 with tetramethylammonium hydroxide solution, add 1.0ml of magnesium chloride (100g / L), and then add 2ml of 25% (v / v) tetramethylammonium hydroxide solution for co-precipitation, transfer the precipitated solution to a 50ml centrifuge tube, centrifuge it at 5000r / min for 5min, discard the supernatant, add 5ml of 65% (v / v) nitric acid solution to dissolve the precipitate, and transfer it to a conical flask, place it on a hot plate and heat it until it is completely dissolved. After complete dissolution, remove it and let it cool, make up to the volume in a 25ml volumetric flask, and at the same time make a reagent blank and shake it for testing.

[0058] (2) Use a 10 mL pipette to accurately transfer the commercially available lead standard solution (1000 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 100 mg / L lead standard stock solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 10 mg / L lead standard intermediate solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L lead standard intermediate solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L lead standard intermediate solution. The standard stock solution (1 mg / L) is placed in a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain a 0.1 mg / L lead standard intermediate solution; 0.0 mL, 1.0 mL, 5.0 mL, 10.0 mL, and 20.0 mL of the 0.1 mg / L lead standard intermediate solution are respectively pipetted into five 100 mL volumetric flasks, and 5.0 mL of the 1 mg / L lead standard intermediate solution is pipetted into a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain 0.0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, and 50 μg / L standard working curve solutions, which are then shaken to obtain the lead standard working curve solution to be tested.

[0059] Accurately pipette the commercially available cadmium standard solution (1000 mg / L) into a 100 mL volumetric flask with a 10 mL pipette, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 100 mg / L cadmium standard stock solution; accurately pipette the cadmium standard stock solution (100 mg / L) into a 100 mL volumetric flask with a 10 mL pipette, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 10 mg / L cadmium standard intermediate solution; accurately pipette the cadmium standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution; accurately pipette the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution; accurately pipette the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution. A quasi-stock solution (1 mg / L) is placed in a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain a 0.1 mg / L cadmium standard intermediate solution; 0.0 mL, 1.0 mL, 5.0 mL, 10.0 mL, and 20.0 mL of the 0.1 mg / L lead standard intermediate solution are respectively pipetted into six 100 mL volumetric flasks, and 5.0 mL of the 1 mg / L cadmium standard intermediate solution is pipetted into a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain standard working curve solutions of 0.0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, and 50 μg / L, and shaken to obtain a cadmium standard working curve solution to be tested.

[0060] (3) Use an Agilent inductively coupled plasma mass spectrometer (Model 7700), turn on the instrument and related auxiliary equipment and computer, and preheat the instrument for 20 minutes.

[0061] (4) Set the instrument test parameters: RF power / 1.55kW, plasma argon gas flow rate / 15.0L.min-1, auxiliary gas flow rate / 1.00L.min-1, pump speed / 15rpm, spray chamber temperature 2℃, spray gas flow rate / 0.70L.min-1, stabilization time / 25s, scanning mode is peak jump, and the number of repetitions is 3 times. After meeting the requirements, complete the test of the lead and cadmium element standard working curves first, and then analyze the reagent blank solution and sample solution, numbered C1-1, C1-2, C1-J1, C1-J2; the lead ion concentrations are 4.3149μg / L, 4.1008μg / L, 12.9068μg / L; 12.8447μg / L respectively;

[0062] The numbers are C1-1, C1-2, C1-J1, and C1-J2; the cadmium ion concentrations are 1.0668μg / L, 1.0901μg / L, 2.9804μg / L, and 2.9211μg / L respectively.

[0063] (5) The lead ion contents in samples numbered C1-1, C1-2, C1-J1, and C1-J2 were calculated to be 0.05372 mg / kg, 0.05125 mg / kg, 0.1612 mg / kg, and 0.1600 mg / kg, respectively; the spiked recoveries were 87.1% and 86.3%, respectively.

[0064] By calculation, the cadmium ion contents in samples numbered C1-1, C1-2, C1-J1, and C1-J2 were 0.01328 mg / kg, 0.01362 mg / kg, 0.03722 mg / kg, and 0.03639 mg / kg, respectively; the spiked recoveries were 94.9% and 91.8%.

[0065] Comparative Example 1

[0066] This comparative example provides a method for determining the content of lead and cadmium in table salt, comprising the following steps:

[0067] Prepare four 150ml conical flasks numbered D1-1, D1-2, D1-J1, and D1-J2, weigh 2.0g (accurate to 0.1mg) of salt sample into each of the four D1 flasks, then add 1.00mL of a mixed standard solution of 250μg / L lead and 50μg / L cadmium to D1-J1 and D1-J2, add 1.00mL of first-grade water to D1-1 and D1-2, and then add 10mL of the mixed standard solution to each conical flask containing the sample. 5% (v / v) nitric acid solution, place it on a 180℃ hot plate and heat it for 20min, remove it and let it cool, add 5ml of water, adjust the pH to 7-8 with tetramethylammonium hydroxide solution, add 0.5ml of magnesium chloride (100g / L), and then add 0.5ml of 25% (v / v) tetramethylammonium hydroxide solution for co-precipitation, transfer the precipitated solution to a 50ml centrifuge tube, centrifuge it at 5000r / min for 5min, discard the supernatant, add 5ml of 65% (v / v) nitric acid solution to dissolve the precipitate, transfer it to a conical flask, place it on a hot plate and heat it until it is completely dissolved, remove it and let it cool after it is completely dissolved, make the volume to a 25ml volumetric flask, and at the same time make a reagent blank and shake it for testing.

[0068] (2) Use a 10 mL pipette to accurately transfer the commercially available lead standard solution (1000 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 100 mg / L lead standard stock solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 10 mg / L lead standard intermediate solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L lead standard intermediate solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L lead standard intermediate solution. The standard stock solution (1 mg / L) is placed in a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain a 0.1 mg / L lead standard intermediate solution; 0.0 mL, 1.0 mL, 5.0 mL, 10.0 mL, and 20.0 mL of the 0.1 mg / L lead standard intermediate solution are respectively pipetted into five 100 mL volumetric flasks, and 5.0 mL of the 1 mg / L lead standard intermediate solution is pipetted into a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain 0.0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, and 50 μg / L standard working curve solutions, which are then shaken to obtain the lead standard working curve solution to be tested.

[0069] Accurately pipette the commercially available cadmium standard solution (1000 mg / L) into a 100 mL volumetric flask with a 10 mL pipette, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 100 mg / L cadmium standard stock solution; accurately pipette the cadmium standard stock solution (100 mg / L) into a 100 mL volumetric flask with a 10 mL pipette, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 10 mg / L cadmium standard intermediate solution; accurately pipette the cadmium standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution; accurately pipette the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution; accurately pipette the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution. A quasi-stock solution (1 mg / L) is placed in a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain a 0.1 mg / L cadmium standard intermediate solution; 0.0 mL, 1.0 mL, 5.0 mL, 10.0 mL, and 20.0 mL of the 0.1 mg / L lead standard intermediate solution are respectively pipetted into six 100 mL volumetric flasks, and 5.0 mL of the 1 mg / L cadmium standard intermediate solution is pipetted into a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain standard working curve solutions of 0.0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, and 50 μg / L, and shaken to obtain a cadmium standard working curve solution to be tested.

[0070] (3) Use an Agilent inductively coupled plasma mass spectrometer (Model 7700), turn on the instrument and related auxiliary equipment and computer, and preheat the instrument for 20 minutes.

[0071] (4) Set the instrument test parameters: RF power / 1.55kW, plasma argon gas flow rate / 15.0L.min-1, auxiliary gas flow rate / 1.00L.min-1, pump speed / 15rpm, spray chamber temperature 2℃, spray gas flow rate / 0.70L.min-1, stabilization time / 25s, scanning mode is peak jump, and the number of repetitions is 3 times. After meeting the requirements, complete the test of the lead and cadmium element standard working curves first, and then analyze the reagent blank solution and sample solution, numbered D1-1, D1-2, D1-J1, D1-J2; the lead ion concentrations are 3.2811μg / L, 3.0716μg / L, 9.7849μg / L; 10.5550μg / L respectively;

[0072] The numbers are D1-1, D1-2, D1-J1, and D1-J2; the cadmium ion concentrations are 0.8761μg / L, 0.8122μg / L, 2.3288μg / L, and 2.1224μg / L respectively.

[0073] (5) The lead ion contents in samples numbered D1-1, D1-2, D1-J1, and D1-J2 were calculated to be 0.04086 mg / kg, 0.03810 mg / kg, 0.1212 mg / kg, and 0.1311 mg / kg, respectively; the spiked recoveries were 65.9% and 73.7%, respectively.

[0074] By calculation, the cadmium ion contents in samples numbered D1-1, D1-2, D1-J1, and D1-J2 were 0.01091 mg / kg, 0.01007 mg / kg, 0.02885 mg / kg, and 0.02635 mg / kg, respectively; the spiked recoveries were 74.1% and 63.8%.

[0075] Comparative Example 2

[0076] This comparative example provides a method for determining the content of lead and cadmium in table salt, comprising the following steps:

[0077] Prepare 4 conical flasks numbered E1-1, E1-2, E1-J1, and E1-J2, weigh 2.0 g (accurate to 0.1 mg) of salt sample into each of the 4 E1 flasks, then add 1.00 mL of a mixed standard solution of 250 μg / L lead and 50 μg / L cadmium to E1-J1 and E1-J2, respectively, add 1.00 mL of first-grade water to E1-1 and E1-2, then add 10 mL of 5% (v / v) nitric acid solution to each conical flask containing the sample, heat on a 180°C hot plate for 20 min, remove and cool, add 5 mL of water, adjust the pH to 7.5 with 25% (v / v) tetramethylammonium hydroxide solution, add 3 mL of magnesium chloride (100 g / L), and then add 3 mL Co-precipitate with 25% tetramethylammonium hydroxide solution, transfer the precipitated solution to a 50ml centrifuge tube, centrifuge at 5000r / min for 5min, discard the upper supernatant, add 5ml 65% (v / v) nitric acid solution to dissolve the precipitate, and transfer it to a conical flask, place it on a hot plate and heat until completely dissolved. After complete dissolution, remove it and let it cool, dilute to a 25ml volumetric flask, and at the same time make a reagent blank and shake it for testing.

[0078] (2) Use a 10 mL pipette to accurately transfer the commercially available lead standard solution (1000 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 100 mg / L lead standard stock solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 10 mg / L lead standard intermediate solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L lead standard intermediate solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L lead standard intermediate solution. The standard stock solution (1 mg / L) is placed in a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain a 0.1 mg / L lead standard intermediate solution; 0.0 mL, 1.0 mL, 5.0 mL, 10.0 mL, and 20.0 mL of the 0.1 mg / L lead standard intermediate solution are respectively pipetted into five 100 mL volumetric flasks, and 5.0 mL of the 1 mg / L lead standard intermediate solution is pipetted into a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain 0.0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, and 50 μg / L standard working curve solutions, which are then shaken to obtain the lead standard working curve solution to be tested.

[0079] Accurately pipette the commercially available cadmium standard solution (1000 mg / L) into a 100 mL volumetric flask with a 10 mL pipette, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 100 mg / L cadmium standard stock solution; accurately pipette the cadmium standard stock solution (100 mg / L) into a 100 mL volumetric flask with a 10 mL pipette, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 10 mg / L cadmium standard intermediate solution; accurately pipette the cadmium standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution; accurately pipette the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution; accurately pipette the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (v / v) nitric acid solution, and shake well to obtain a 1 mg / L cadmium standard intermediate solution. A quasi-stock solution (1 mg / L) is placed in a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain a 0.1 mg / L cadmium standard intermediate solution; 0.0 mL, 1.0 mL, 5.0 mL, 10.0 mL, and 20.0 mL of the 0.1 mg / L lead standard intermediate solution are respectively pipetted into six 100 mL volumetric flasks, and 5.0 mL of the 1 mg / L cadmium standard intermediate solution is pipetted into a 100 mL volumetric flask, diluted to the mark with 2% (v / v) nitric acid solution, and shaken to obtain standard working curve solutions of 0.0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, and 50 μg / L, and shaken to obtain a cadmium standard working curve solution to be tested.

[0080] (3) Use an Agilent inductively coupled plasma mass spectrometer (Model 7700), turn on the instrument and related auxiliary equipment and computer, and preheat the instrument for 20 minutes.

[0081] (4) Set the instrument test parameters: RF power / 1.55kW, plasma argon gas flow rate / 15.0L.min-1, auxiliary gas flow rate / 1.00L.min-1, pump speed / 15rpm, spray chamber temperature 2℃, spray gas flow rate / 0.70L.min-1, stabilization time / 25s, scanning mode is peak jump, and the number of repetitions is 3 times. After meeting the requirements, complete the test of the lead and cadmium element standard working curves first, and then analyze the reagent blank solution and sample solution, numbered E1-1, E1-2, E1-J1, E1-J2; the lead ion concentrations are 2.6869μg / L, 2.3427μg / L, 10.1824μg / L; 9.1081μg / L respectively;

[0082] The numbers are E1-1, E1-2, E1-J1, and E1-J2; the cadmium ion concentrations are 0.9127μg / L, 0.9558μg / L, 2.6771μg / L, and 2.7987μg / L respectively.

[0083] (5) The lead ion contents in samples numbered E1-1, E1-2, E1-J1, and E1-J2 were calculated to be 0.03352 mg / kg, 0.02913 mg / kg, 0.1267 mg / kg, and 0.1137 mg / kg, respectively; the spiked recoveries were 66.79% and 56.16%, respectively.

[0084] By calculation, the cadmium ion contents in samples numbered E1-1, E1-2, E1-J1, and E1-J2 were 0.01138 mg / kg, 0.01188 mg / kg, 0.03331 mg / kg, and 0.03494 mg / kg, respectively; the spiked recoveries were 87.25% and 93.48%.

[0085] Comparative Example 3

[0086] This comparative example provides a method for determining the content of lead and cadmium in table salt, comprising the following steps:

[0087] Prepare 4 conical flasks numbered F1-1, F1-2, F1-J1, and F1-J2, and weigh 2.0 g (accurate to 0.1 mg) of salt sample into each of the 4 F1 flasks. Then, add 1.00 mL of a mixed standard solution of 250 μg / L lead and 50 μg / L cadmium to F1-J1 and F1-J2, respectively. Add 1.00 mL of first-grade water to F1-1 and F1-2, respectively. Then, add 10 mL of 5% (v / v) nitric acid solution to each conical flask containing the sample, place on a 180°C hot plate and heat for 20 minutes, remove and cool, and add 5 ml Water, adjust the pH value to 7-8 with 25% tetramethylammonium hydroxide solution, add 1.5ml magnesium chloride (100g / L), and then add 0.75ml25% (v / v) tetramethylammonium hydroxide solution for co-precipitation, transfer the precipitated solution to a 50ml centrifuge tube, centrifuge at 5000r / min for 5min, discard the upper supernatant, add 5ml65% (v / v) nitric acid solution to dissolve the precipitate, and transfer it to a conical flask, place it on a hot plate and heat until completely dissolved. After complete dissolution, remove it and let it cool, make up to the volume in a 25ml volumetric flask, and at the same time make a reagent blank and shake it for testing.

[0088] (2) Use a 10 mL pipette to accurately transfer the commercially available lead standard solution (1000 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (V / V) nitric acid solution, and shake well to obtain a 100 mg / L lead standard stock solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (V / V) nitric acid solution, and shake well to obtain a 10 mg / L lead standard intermediate solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (V / V) nitric acid solution, and shake well to obtain a 1 mg / L lead standard intermediate solution; Use a 10 mL pipette to accurately transfer the lead standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (V / V) nitric acid solution, and shake well to obtain a 1 mg / L lead standard intermediate solution. The standard stock solution (1 mg / L) is placed in a 100 mL volumetric flask, diluted to the mark with 2% (V / V) nitric acid solution, and shaken to obtain a 0.1 mg / L lead standard intermediate solution; 0.0 mL, 1.0 mL, 5.0 mL, 10.0 mL, and 20.0 mL of the 0.1 mg / L lead standard intermediate solution are respectively pipetted into five 100 mL volumetric flasks, and 5.0 mL of the 1 mg / L lead standard intermediate solution is pipetted into a 100 mL volumetric flask, diluted to the mark with 2% (V / V) nitric acid solution, and shaken to obtain 0.0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, and 50 μg / L standard working curve solutions, which are then shaken to obtain the lead standard working curve solution to be tested.

[0089] Accurately pipette the commercially available cadmium standard solution (1000 mg / L) into a 100 mL volumetric flask with a 10 mL pipette, dilute to the mark with 2% (V / V) nitric acid solution, and shake to obtain a 100 mg / L cadmium standard stock solution; accurately pipette the cadmium standard stock solution (100 mg / L) into a 100 mL volumetric flask with a 10 mL pipette, dilute to the mark with 2% (V / V) nitric acid solution, and shake to obtain a 10 mg / L cadmium standard intermediate solution; accurately pipette the cadmium standard stock solution (10 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (V / V) nitric acid solution, and shake to obtain a 1 mg / L cadmium standard intermediate solution; accurately pipette the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (V / V) nitric acid solution, and shake to obtain a 1 mg / L cadmium standard intermediate solution; accurately pipette the lead standard stock solution (100 mg / L) into a 100 mL volumetric flask, dilute to the mark with 2% (V / V) nitric acid solution, and shake to obtain a 1 mg / L cadmium standard intermediate solution. A quasi-stock solution (1 mg / L) is placed in a 100 mL volumetric flask, diluted to the mark with a 2% (V / V) nitric acid solution, and shaken to obtain a 0.1 mg / L cadmium standard intermediate solution; 0.0 mL, 1.0 mL, 5.0 mL, 10.0 mL, and 20.0 mL of the 0.1 mg / L lead standard intermediate solution are respectively pipetted into six 100 mL volumetric flasks, and 5.0 mL of the 1 mg / L cadmium standard intermediate solution is pipetted into a 100 mL volumetric flask, diluted to the mark with a 2% (V / V) nitric acid solution, and shaken to obtain standard working curve solutions of 0.0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L, and 50 μg / L, and shaken to obtain a cadmium standard working curve solution to be measured.

[0090] (3) Use an Agilent inductively coupled plasma mass spectrometer (Model 7700), turn on the instrument and related auxiliary equipment and computer, and preheat the instrument for 20 minutes.

[0091] (4) Set the instrument test parameters: RF power / 1.55kW, plasma argon gas flow rate / 15.0L.min-1, auxiliary gas flow rate / 1.00L.min-1, pump speed / 15rpm, spray chamber temperature 2℃, spray gas flow rate / 0.70L.min-1, stabilization time / 25s, scanning mode is peak jump, and the number of repetitions is 3 times. After meeting the requirements, complete the test of the lead and cadmium element standard working curves first, and then analyze the reagent blank solution and sample solution, numbered F1-1, F1-2, F1-J1, F1-J2; the lead ion concentrations are 2.7811μg / L, 2.4093μg / L, 8.6849μg / L; 9.1372μg / L respectively;

[0092] The numbers are F1-1, F1-2, F1-J1, and F1-J2; the cadmium ion concentrations are 0.7854μg / L, 0.7629μg / L, 2.1374μg / L, and 2.0224μg / L respectively.

[0093] (5) The lead ion contents in samples numbered F1-1, F1-2, F1-J1, and F1-J2 were calculated to be 0.03464 mg / kg, 0.02989 mg / kg, 0.1076 mg / kg, and 0.1135 mg / kg, respectively; the spiked recoveries were 60.7% and 65.3%, respectively.

[0094] By calculation, the cadmium ion contents in samples numbered F1-1, F1-2, F1-J1, and F1-J2 were 0.00978 mg / kg, 0.00946 mg / kg, 0.02648 mg / kg, and 0.02762 mg / kg, respectively; the spiked recoveries were 64.5% and 68.8%.

[0095] As can be seen from the above results, in Examples 1-3, by adjusting the pH value of the solution and controlling the amount of magnesium chloride and tetramethylammonium hydroxide added, lead, cadmium, and magnesium ions in the solution can be coprecipitated well, with the lead spike recovery rate reaching over 80%, and the cadmium spike recovery rate reaching over 90%, enabling accurate and rapid determination of lead and cadmium in table salt. Compared to Example 1, Example 2 uses sodium hydroxide to adjust the pH value of the solution. The sodium ions in the sodium hydroxide in the solution produce background interference on the test of lead and cadmium ions, and have a certain impact on the lead hydroxide precipitate. Therefore, its spike recovery rate is slightly worse than that of Example 1. Embodiment 1 is compared with Comparative Example 1, Comparative Example 2, and the consumption of magnesium chloride is too little or the consumption is too much, and the effect of precipitated lead is all undesirable, and the recovery of its lead is all only about 65%, and the consumption of magnesium chloride is too little and also affects the recovery of cadmium simultaneously, and the recovery of cadmium is all only about 75%, and larger deviation is arranged, illustrating that the use of magnesium chloride and its consumption have great influence on the measurement result of lead and cadmium content in table salt.Comparative Example 3 is compared with Example 1, and under specific concentration, the volume ratio of the magnesium chloride solution added and tetramethylammonium hydroxide solution is 2:1, can cause the magnesium ion added can not be precipitated completely, and the effect of precipitated lead and cadmium is all undesirable, and the recovery of its lead and cadmium is all only about 65%, and larger deviation is arranged, illustrating that the amount ratio of magnesium chloride and tetramethylammonium hydroxide also has influence on the measurement result of lead and cadmium content in table salt.

[0096] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0097] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing a sample for determining the content of lead and cadmium in table salt, characterized in that: The steps include: Adding a digestion solution to the salt sample to be tested to digest the sample and obtain a digestion solution; Add magnesium chloride solution to the digestion solution and mix well. After adjusting the pH value of the solution to 7-8, add tetramethylammonium hydroxide solution to obtain a precipitate. Add nitric acid solution to the precipitate and dissolve it to obtain the test sample.

2. The method for preparing a sample for determining the content of lead and cadmium in table salt according to claim 1, wherein: When the added salt sample to be tested is 1.5 mg to 2.5 mg, the concentration of the added magnesium chloride solution is 90 g / L to 110 g / L, and the amount added is 1 mL to 2 mL.

3. The method for preparing a sample for determining the content of lead and cadmium in table salt according to claim 2, wherein: When the added salt sample to be tested is 1.8 mg to 2.2 mg, the concentration of the added magnesium chloride solution is 98 g / L to 102 g / L, and the added amount is 1 mL to 1.5 mL.

4. The method for preparing a sample for determining the content of lead and cadmium in table salt according to claim 2, wherein: The concentration of the added tetramethylammonium hydroxide solution is 23% to 27% (v / v), and the amount added is 1.5 mL to 3 mL.

5. The method for preparing a sample for determining the content of lead and cadmium in table salt according to claim 4, wherein: The volume ratio of the added magnesium chloride solution to the tetramethylammonium hydroxide solution is 1:1-2.

6. The method for preparing a sample for determining the content of lead and cadmium in table salt according to claim 1, wherein: The pH value of the solution is adjusted using tetramethylammonium hydroxide solution and / or sodium hydroxide solution.

7. The method for preparing a sample for determining the content of lead and cadmium in table salt according to claim 2, wherein: The digestion solution is a 4-6% (v / v) nitric acid solution, and the amount added is 8 mL to 12 mL.

8. The method for preparing a sample for determining the content of lead and cadmium in table salt according to claim 1, wherein: The step of adding a digestion solution to the salt sample to be tested to digest the sample to obtain a digestion solution comprises the following steps: After adding the digestion solution to the salt sample to be tested, heating and digesting at 175° C. to 185° C. for 18 min to 22 min, and cooling to obtain the digestion solution.

9. A test sample for determining the content of lead and cadmium in table salt, prepared by the preparation method according to any one of claims 1 to 8.

10. A method for determining the content of lead and cadmium in table salt, characterized in that: The following steps are involved: The content of lead and cadmium in the test sample according to claim 9 is determined by inductively coupled plasma mass spectrometry.