A detection method for separating, enriching and desorbing lead ions in table salt based on diatomite

Abstract

This case involves a detection method for separating, enriching and desorbing lead ions in table salt based on diatomaceous earth, including enrichment and desorption: the lead ions in table salt are separated and enriched under alkaline conditions, then desorbed under acidic conditions, and then the collected desorbed solution is detected by a graphite furnace atomic absorption spectrometer, and the concentration of lead ions in the sample is converted by the standard curve method. This case is based on the common reagent diatomaceous earth, and the enrichment and desorption of lead ions in table salt can be completed without chemical modification, greatly reducing the matrix interference problem, being able to accurately determine the content of lead ions in table salt, with relatively high method sensitivity and recovery rate; the operation steps are simple, greatly simplifying the detection steps of lead ions in table salt, and can effectively improve the analysis efficiency, being conducive to the analysis and detection of batch samples; being conducive to popularization and application in daily laboratory tests; the method described in the present invention uses low-cost reagents, does not require organic solvents to participate, and does not introduce other metal ions, having the advantages of environmental friendliness.

Description

Technical Field

[0001] The present invention relates to a method for determining lead ions in table salt, and particularly to a detection method for separating, enriching and desorbing lead ions in table salt based on diatomite. Background Art

[0002] There are a large number of sodium, potassium, calcium and other ions in high-salt matrix samples (such as table salt, brine, soy sauce and pickled foods, etc.). The presence of these ions causes a large amount of spectral interference and matrix interference when determining trace heavy metal ions. When using graphite furnace atomic absorption spectrometry for determination, salts accumulate on the graphite tube, greatly shortening the life of the graphite tube. When using ICP-MS for determination, it may also cause clogging of the nebulizer and salt deposition on the torch tube and reaction cone. Therefore, the determination of trace heavy metals in high-salt matrix samples has always been a difficult point in analytical testing.

[0003] Currently, in order to solve the above problems, methods such as matrix modification method, extraction method and coprecipitation method are adopted. For high-salt matrix samples, through experiments, it is proved that the matrix modification method cannot overcome a large amount of background interference, and thus cannot achieve accurate quantitative determination of trace heavy metals. In daily detection, the liquid-liquid extraction method is commonly used to determine the lead ion content in table salt. However, this method is not only cumbersome to operate, but also uses a large amount of the organic extraction solution methyl isobutyl ketone (MIBK). And MIBK has a relatively pungent smell, which can cause nausea, vomiting, loss of appetite, abdominal pain, as well as irritation symptoms of the respiratory tract and skin. Inhalation of a large amount can cause inhibition and anesthesia of the central nervous system. At the same time, due to the certain volatility of MIBK, it has a greater impact on the precision and accuracy of experimental data. The coprecipitation method can effectively reduce the use of organic solvents and is more convenient to operate at the same time. However, the coprecipitation reagents added are generally transition metal hydroxides such as lanthanide series and actinide series, and the introduction of some elements will also cause greater background absorption interference. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, the purpose of the present invention is to establish a method that can quickly separate the target ions, eliminate the interference of matrix interference ions on spectral analysis, and achieve accurate quantitative determination of trace heavy metal lead ions.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A detection method for separating, enriching and desorbing lead ions in table salt based on diatomite, comprising the following steps:

[0007] 1) Enrichment and desorption:

[0008] a) Take a table salt sample, dissolve it with deionized water, and then transfer it to a centrifuge tube;

[0009] b) Add diatomite and an alkaline buffer solution to the centrifuge tube;

[0010] c) After shaking the centrifuge tube well, take it out for centrifugation and discard the supernatant;

[0011] d) Add 5% HNO3 to the centrifuge tube, shake for 15 - 30 min, and then centrifuge to obtain the desorption solution;

[0012] 2) Detection:

[0013] Detect using a graphite furnace atomic absorption spectrometer: Method parameters: Detection wavelength 217.3 nm, slit width 0.7 nm;

[0014] 3) Result calculation:

[0015] Standard curve method. By measuring the intensity of lead ions in the desorption solution and substituting it into the standard curve equation, the concentration of lead ions in the sample is converted.

[0016] Preferably, in the step 1), the mass ratio of table salt to diatomaceous earth is 1:0.01 - 0.02.

[0017] Preferably, in the step c), the pH value range after adding the alkaline buffer solution is 10 - 12.

[0018] Preferably, in the step c), the centrifuge tube is shaken for 30 min in an environment of 50 °C.

[0019] Preferably, in the step c), the centrifuge tube is centrifuged at 5000 rmp / s for 10 min.

[0020] Preferably, the content of SiO2 in the diatomaceous earth is ≥85.0%.

[0021] The beneficial effects of the present invention are as follows: Based on the common reagent diatomaceous earth, this case can complete the enrichment and desorption of lead ions in table salt without chemical modification, greatly reducing the matrix interference problem, and can accurately determine the content of lead ions in table salt. The method has high sensitivity and recovery rate; the operation steps are simple, greatly simplifying the detection steps of lead ions in table salt, can effectively improve the analysis efficiency, and is conducive to the analysis and detection of batch samples; it is conducive to popularization and application in daily laboratory tests; the method of the present invention uses reagents with low cost, does not require organic solvents to participate, and does not introduce other metal ions, having the advantages of environmental friendliness. Description of the drawings

[0022] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 It is a curve graph showing the adsorption rate relationship of diatomite to lead and sodium ions at different pH values. Specific implementation manners

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] Instruments and reagents used in this case: Atomic absorption spectrometer (PE AA900t); Ultrapure water instrument (Millipore); Oscillating thermostat (Guohua Instrument Manufacturing Co., Ltd.); Lead standard solution (National Nonferrous Metals); Diatomite (Sinopharm Chemical Reagent Co., Ltd., SiO2 content ≥ 85.0%, AR).

[0027] Detection by graphite furnace atomic absorption spectrometer: Method parameters: Detection wavelength 217.3 nm, slit width 0.7 nm, standard series: 2.5, 5, 10, 20, 50 μg / L.

[0028] After the lead standard solutions of each concentration are determined by graphite furnace atomic absorption spectrometer, the standard curve equation of lead element concentration and absorbance is obtained: y = 0.00428x + 0.00087, and the linear coefficient is 0.99988.

[0029] Example 1:

[0030] Weigh the lead standard solution and sodium standard solution, add 15 ml of water to simulate the salt solution to be measured. The contents of Pb 2+ and Na + in the salt solution are 10 μg and 1000 μg respectively;

[0031] Take 8 50-ml centrifuge tubes, add the salt solution to be measured into them, add 0.2 g of diatomite, then adjust the pH of the solution to 2, 4, 6, 7, 8, 10, 11, 12 respectively, add water to 25 ml, put the centrifuge tubes into a 50 °C oscillating constant temperature water bath and shake for 30 min, then take them out. Centrifuge at 5000 rmp / s for 10 min, collect the supernatant (adsorption solution), and measure the lead ion and sodium ion concentrations respectively by graphite furnace and flame atomic absorption methods, and calculate the adsorption rate R1 of the two elements through the formula.

[0032] R1 = 100 × (1 - m 吸附 / m 添加 );

[0033] Desorption: Continue to add 25 mL of 5% HNO3 solution to the centrifuge tube, shake at room temperature for 30 min. Then centrifuge at 5000 rmp / s for 10 min. Take the supernatant (desorbing solution) and measure the lead ion concentration by graphite furnace. Calculate the recovery rate R2 through the formula.

[0034] R2 = 100×(m 解吸附 / m 添加 ); where

[0035] m 添加 : The mass (μg) of added Pb 2+ or Na + ;

[0036] m 吸附 : The mass (μg) of residual ions in the adsorption solution

[0037] m 解吸附 : The mass (μg) of ions in the desorbing solution.

[0038] As Figure 1 shown, whether under acidic or alkaline conditions, diatomaceous earth hardly adsorbs Na + . However, under alkaline conditions, especially when pH = 10 - 12, the adsorption of lead ions by diatomaceous earth can reach over 90%, and under acidic conditions, it can be almost completely desorbed, and the measurement results are relatively accurate.

[0039] Example 2

[0040] Add 15 mL of ultrapure water and 0.1 g of diatomaceous earth to a 50 mL centrifuge tube containing 1000 μg of Pb 2+ . Add 5 mL of buffer solution (pH = 10), place the centrifuge tube in a 50°C shaking constant temperature water bath, shake for 30 min, and then take it out. Centrifuge at 5000 rmp / s for 10 min. Determine the lead ion content in the supernatant by graphite furnace atomic absorption spectrometry, and finally obtain the lead ion adsorption capacity result of diatomaceous earth (Table 1). The calculation method of the adsorption amount is: adsorption capacity = (added amount - content of the target substance in the solution after adsorption) / mass of diatomaceous earth.

[0041] Table 1

[0042]

[0043] As can be seen from Table 1, the adsorption capacity of diatomite for lead ions can reach 9891 μg / g. In the national food safety standard "Limits of Contaminants in Foods" (GB2762-2017), the lead element limit for table salt is 2.0 μg / g. If 10 g of the sample is taken, the lead content is 20 μg, and actually 2 mg of diatomite is required. Considering the operability of the experiment and the convenience of centrifugation, using 0.1 - 0.2 g of diatomite as the adsorbent can ensure meeting the detection requirements for the lead content in conventional foods.

[0044] Although the embodiments of the present invention have been disclosed as above, it is not limited to only the applications listed in the specification and the embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details and the illustrated and described examples here.

Claims

1. A detection method for separating, enriching and desorbing lead ions in table salt based on diatomite, characterized in that, It includes the following steps: 1) Enrichment and desorption: a) Take a salt sample, dissolve it in deionized water, and then transfer it to a centrifuge tube; b) Add diatomaceous earth and an alkaline buffer solution to the centrifuge tube; c) Oscillate the centrifuge tube in an environment of 50 °C for 30 min. After shaking well, take it out for centrifugation, centrifuge at 5000 rmp / s for 10 min, and discard the supernatant; d) Add 5% HNO3 to the centrifuge tube, oscillate for 15 - 30 min, and then centrifuge to obtain a desorption solution; 2) Detection: Detect using a graphite furnace atomic absorption spectrometer: Method parameters: Detection wavelength 217.3 nm, slit width 0.7 nm; 3) Result calculation: Standard curve method. By measuring the lead ion intensity in the desorption solution and substituting it into the standard curve equation, the lead ion concentration in the sample is converted; In step b), the pH value range after adding the alkaline buffer solution is 10 - 12.

2. The detection method for separating, enriching and desorbing lead ions in table salt based on diatomaceous earth as claimed in claim 1, wherein, In step 1), the mass ratio of salt to diatomaceous earth is 1:0.01 - 0.

02.

3. The detection method for separating, enriching and desorbing lead ions in table salt based on diatomaceous earth as claimed in claim 1, wherein The content of SiO2 in the diatomaceous earth is ≥85.0%.

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