Method for measuring content of trace cadmium in stainless steel

Abstract

The invention relates to a method for determining the content of trace cadmium in stainless steel, and belongs to the technical field of element detection. The method comprises the following steps: obtaining a stainless steel sample solution with a set pH value; adding a lead acetate solution into the stainless steel sample solution to generate a lead molybdate precipitate so as to obtain a first mixture containing the lead molybdate precipitate; fixing the volume of the first mixture to obtain a to-be-detected sample mixture; performing solid-liquid separation on the to-be-detected sample mixture to obtain a to-be-detected sample solution; preparing a series concentration solution of the cadmium element, and drawing a cadmium element standard curve according to the series concentration solution; and obtaining the cadmium content in the stainless steel sample according to the cadmium element standard curve. According to the method, the pH value in the stainless steel sample solution is adjusted to be a set value, conditions are provided for generating lead molybdate sediment, molybdenum is separated, signal interference or background interference generated in cadmium content determination is avoided, and the accuracy and reliability of a detection result are remarkably improved.

Description

Technical Field

[0001] The present application relates to the technical field of metal content determination, and in particular to a method for determining trace cadmium content in stainless steel. Background Art

[0002] Stainless steel is widely used in numerous fields due to its excellent corrosion resistance, atmospheric corrosion resistance, and high-temperature strength. Depending on the elemental content, stainless steel can be adapted to different applications. However, in fields such as food and medical treatment, where material safety is paramount, controlling the cadmium content in stainless steel is particularly important. Studies have shown that if the cadmium content in stainless steel exceeds the standard, the cadmium may migrate into and accumulate in the body when used in food contact materials or medical devices. Cadmium that enters the human body binds to thioproteins to form cadmium thioproteins, which are distributed throughout the body through the bloodstream and specifically accumulate in organs such as the kidneys and liver, posing a potential threat to the body.

[0003] Currently, domestic and international testing for cadmium in stainless steel primarily focuses on determining its dissolution or migration, with relevant standards and methods primarily developed around this objective. However, no methods or standards have been reported for determining the specific cadmium content in the stainless steel matrix. The lack of such a method makes it difficult to control the source of cadmium in stainless steel raw materials and restricts the safer use of stainless steel in sensitive applications such as food and medicine. Therefore, establishing an accurate and reliable method for determining cadmium content in stainless steel matrix is of great practical significance. Summary of the Invention

[0004] The present application provides a method for determining the trace cadmium content in stainless steel to solve the following technical problem: how to provide a method for accurately determining the cadmium content in stainless steel.

[0005] The present invention provides a method for determining the trace cadmium content in stainless steel, comprising the following steps:

[0006] obtaining a stainless steel sample solution having a set pH value;

[0007] adding a lead acetate solution to the stainless steel sample solution to generate a lead molybdate precipitate, thereby obtaining a first mixture containing the lead molybdate precipitate;

[0008] The first mixture is fixed to volume to obtain a sample mixture to be tested;

[0009] Performing solid-liquid separation on the sample mixture to obtain a sample solution;

[0010] preparing a series of concentration solutions of the cadmium element, and drawing a cadmium element standard curve based on the series of concentration solutions;

[0011] The cadmium content in the stainless steel sample is obtained according to the cadmium element standard curve.

[0012] Optionally, obtaining the stainless steel sample solution with a set pH value specifically includes:

[0013] Accurately weigh stainless steel samples;

[0014] dissolving the stainless steel sample with a mixed acid solution to obtain a second mixture;

[0015] adding perchloric acid to the second mixture, and heating the second mixture containing the perchloric acid to obtain a third mixture;

[0016] adding a hydrochloric acid solution to the third mixture;

[0017] The pH of the third mixture containing the hydrochloric acid solution is adjusted to obtain a stainless steel sample solution with a set pH value.

[0018] Optionally, the mixed acid includes concentrated nitric acid, concentrated hydrochloric acid and hydrofluoric acid.

[0019] Optionally, the volume ratio of concentrated nitric acid, concentrated hydrochloric acid and hydrofluoric acid in the mixed acid is 2-3:10-15:1-2.

[0020] Optionally, adjusting the pH of the third mixture containing the hydrochloric acid solution to obtain a stainless steel sample solution having a set pH value specifically includes:

[0021] adding concentrated aqueous ammonia dropwise to the third mixture containing the hydrochloric acid solution until the precipitation no longer increases, to obtain a fourth mixture;

[0022] An acetic acid-ammonium acetate buffer solution is added to the fourth mixture to obtain a stainless steel sample solution with a set pH value.

[0023] Optionally, the step of adding a lead acetate solution to the stainless steel sample solution to generate a lead molybdate precipitate to obtain a first mixture containing the lead molybdate precipitate specifically includes:

[0024] adding lead acetate solution to the stainless steel sample solution;

[0025] heating the stainless steel sample solution containing the lead acetate solution to a first preset temperature;

[0026] Insulating the stainless steel sample solution containing the lead acetate solution under the first preset temperature and preset time conditions;

[0027] After the heat preservation is completed, the stainless steel sample solution containing the lead acetate solution is cooled to room temperature to obtain a first mixture containing lead molybdate precipitate.

[0028] Optionally, the first preset temperature is 80°C to 100°C, and the preset time is 0.8h to 1.2h.

[0029] Optionally, the step of adjusting the volume of the first mixture to obtain a sample mixture to be tested further comprises:

[0030] An acetic acid-ammonium acetate buffer solution is added to the mixture to obtain a first mixture having the set pH value.

[0031] Optionally, the series of concentration solutions of cadmium element have the set pH value.

[0032] Optionally, inductively coupled plasma mass spectrometry is used to determine the cadmium content in the series of concentration solutions of the cadmium element and the sample solution to be tested.

[0033] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0034] The embodiment of the present application provides a method for determining the trace cadmium content in stainless steel, comprising the following steps: obtaining a stainless steel sample solution with a set pH value to ensure that a uniform sample solution can meet subsequent precipitation requirements; adding a lead acetate solution to the stainless steel sample solution to completely generate a lead molybdate precipitate, so that the molybdenum element is completely separated from the sample solution to avoid the influence of the subsequent molybdenum element, and obtaining a first mixture containing the lead molybdate precipitate; constant-volume the first mixture to obtain a sample mixture to be tested, accurately obtaining the volume of the sample mixture to be tested, and facilitating subsequent quantitative analysis; performing solid-liquid separation on the sample mixture to be tested to obtain a sample solution to be tested, and avoiding clogging of the detection equipment by the precipitation and interference with the detection results; preparing a series of cadmium element concentration solutions, and drawing a cadmium element standard curve based on the series of concentration solutions, establishing a quantitative relationship between the cadmium concentration and the instrument signal value, correcting the instrument error, and providing a basis for subsequent quantitative analysis, thereby obtaining the cadmium content in the stainless steel sample according to the cadmium element standard curve.

[0035] In this method, by adjusting the pH of the stainless steel sample solution to a set value, optimal reaction conditions are provided for the subsequent addition of lead acetate to form a lead molybdate precipitate. This lead molybdate precipitate selectively separates molybdenum, thereby preventing signal or background interference in cadmium determination, significantly improving the accuracy and reliability of the test results. This optimization results in more accurate cadmium content data, providing a more reliable scientific basis for evaluating the suitability of stainless steel materials in fields such as food and medicine. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0037] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0038] Figure 1 1 is a flow chart of a method for determining cadmium content in stainless steel according to some embodiments of the present application;

[0039] Figure 2 This is a flow chart of a method for determining the cadmium content in stainless steel provided in Example 1 of the present application. DETAILED DESCRIPTION

[0040] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0041] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values within the range; for example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range; in addition, whenever a numerical range is indicated in this document, it is meant to include any cited number (fractional or integer) within the indicated range.

[0042] As used herein, the terms "including," "comprising," and the like mean "including but not limited to." Relational terms such as "first" and "second" are used solely to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. "And / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, "A and / or B" can mean: A exists alone, A and B exist at the same time, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, "plurality" means two or more; "at least one," "at least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items; for example, "at least one of a, b, or c" or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or plural. "Parts" notation, such as parts by weight or parts by mass, indicates the proportional relationship between components. In this article, the parameters described by ratio should be understood as the first term of the proportional formula, in the order in which they are described, and the proportional figures should be understood as the second term. For example, if the mass ratio of substances A, B, and C is 1:2:3, then substances A, B, and C should correspond to the proportional figures in the proportional formula, in the order in which they are described: that is, the mass of substance A:the mass of substance B:the mass of substance C = 1:2:3.

[0043] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this article can be purchased from the market or prepared by existing methods.

[0044] Figure 1 Schematic diagram of a process for determining trace cadmium content in stainless steel according to some embodiments of the present application;

[0045] like Figure 1 As shown, the embodiment of the present application provides a method for determining the trace cadmium content in stainless steel, comprising the following steps:

[0046] S1, obtaining a stainless steel sample solution with a set pH value;

[0047] In step S1, a stainless steel sample is first dissolved in an appropriate solvent to obtain a stainless steel sample solution, and then the pH of the stainless steel sample solution is adjusted to a set value by adding certain reagents, thereby providing optimized conditions for subsequent reactions;

[0048] S2, adding a lead acetate solution to the stainless steel sample solution to generate a lead molybdate precipitate, thereby obtaining a first mixture containing the lead molybdate precipitate;

[0049] In step S2, a lead acetate solution is added to the stainless steel sample solution with a set pH value, and the lead ions react with the molybdenum element (molybdate ion) in the solution to form a lead molybdate precipitate, so that the molybdenum element is stripped from the solution to avoid interference with the measurement results during the subsequent cadmium content determination.

[0050] S3, adjusting the volume of the first mixture to obtain a sample mixture to be tested;

[0051] In step S3, the first mixture containing the lead molybdate precipitate is fixed to a volume V, thereby diluting or adjusting the solution to a known and accurate volume V so that subsequent analysis and calculation can be performed based on a unified volume standard. The content or concentration of the target substance can then be directly calculated using a formula.

[0052] S4, performing solid-liquid separation on the sample mixture to obtain a sample solution;

[0053] In step S4, the sample mixture to be tested after the volume is fixed is subjected to solid-liquid separation to remove the generated lead molybdate precipitate, leaving a solution that does not contain molybdenum element for subsequent cadmium content determination to prevent the precipitation from clogging the instrument sampling tube during the test and affecting the measurement results.

[0054] S5, preparing a series of concentration solutions of the cadmium element, and drawing a cadmium element standard curve according to the series of concentration solutions;

[0055] In step S5, a series of cadmium element concentration solutions are first prepared as standard curve solutions, and the cadmium content in the standard curve solutions is determined by a detection device and a standard curve is drawn to establish a quantitative relationship between the cadmium element concentration and the instrument response signal, and calibrate the instrument, so that the cadmium element content in the sample solution can be accurately determined, thereby improving the measurement accuracy.

[0056] S6, obtaining the cadmium content in the stainless steel sample according to the cadmium element standard curve;

[0057] In step S6, the sample filtrate to be tested needs to be detected by a detection means first to obtain a corresponding instrument response signal, and then the concentration c of the cadmium element in the sample filtrate can be determined according to the standard curve drawn in step S5, and finally the cadmium content in the stainless steel sample is obtained.

[0058] In the above embodiment, a stainless steel sample solution with a set pH value is first obtained to ensure that a uniform sample solution can meet subsequent precipitation requirements; a lead acetate solution is added to the stainless steel sample solution to completely generate a lead molybdate precipitate, so that the molybdenum element is completely separated from the sample solution, avoiding the influence of the subsequent molybdenum element, and obtaining a first mixture containing the lead molybdate precipitate; the first mixture is constant to volume to obtain a sample mixture to be tested, and the volume of the sample mixture to be tested is accurately obtained to facilitate subsequent quantitative analysis; the sample mixture to be tested is subjected to solid-liquid separation to obtain a sample solution to be tested, avoiding clogging of the detection equipment by the precipitation and interference with the test results; a series of cadmium element concentration solutions are prepared, and a cadmium element standard curve is drawn based on the series of concentration solutions, a quantitative relationship between the cadmium concentration and the instrument signal value is established, the instrument error is corrected, and a basis for subsequent quantitative analysis is provided, thereby obtaining the cadmium content in the stainless steel sample based on the cadmium element standard curve.

[0059] In this method, by adjusting the pH of the stainless steel sample solution to a set value, optimal reaction conditions are provided for the subsequent addition of lead acetate to form a lead molybdate precipitate. This lead molybdate precipitate selectively separates molybdenum, thereby preventing signal or background interference in cadmium determination, significantly improving the accuracy and reliability of the test results. This optimization results in more accurate cadmium content data, providing a more reliable scientific basis for evaluating the suitability of stainless steel materials in fields such as food and medicine.

[0060] As an optional embodiment, obtaining a stainless steel sample solution with a set pH value specifically includes:

[0061] S11, accurately weigh the stainless steel sample;

[0062] In step S11 , the mass m of the stainless steel sample is accurately weighed to facilitate subsequent accurate calculation of the cadmium content in the stainless steel sample.

[0063] S12, dissolving the stainless steel sample with a mixed acid solution to obtain a second mixture;

[0064] In step S12, an appropriate solvent, such as a mixed acid solution, is used to fully dissolve the cadmium, molybdenum, iron and other metal elements in the stainless steel sample, so as to facilitate subsequent processing and cadmium content determination.

[0065] S13, adding perchloric acid to the second mixture, and heating the second mixture containing perchloric acid to obtain a third mixture;

[0066] S13: When using a mixed acid to dissolve the stainless steel sample, nitrogen oxides, fluorides, and the like may be present in the mixed acid, and therefore need to be removed. Perchloric acid is added to the second mixture and heated to near dryness to drive out the hydrofluoric acid and nitrogen oxides in the solution.

[0067] S14, adding a hydrochloric acid solution to the third mixture;

[0068] In step S14, concentrated hydrochloric acid and deionized water are added to the third mixture to dissolve the third mixture again, dissolve the metal elements again, and obtain a stainless steel sample solution.

[0069] S15, adjusting the pH of the third mixture containing the hydrochloric acid solution to obtain a stainless steel sample solution with a set pH value;

[0070] In step S15, the pH is adjusted to meet the requirements of the subsequent precipitation reaction.

[0071] In the above embodiment, after accurately obtaining the mass m of the stainless steel sample, because stainless steel is insoluble in common reagents, it is first dissolved in a mixed acid solution to disperse the elements in the stainless steel, such as cadmium, molybdenum, and iron, into the solution. Since the mixed acid may contain nitrogen oxides and fluorides, these need to be removed. In this embodiment, perchloric acid is used and heated to near dryness to drive out the hydrofluoric acid and nitrogen oxides in the solution, resulting in a third mixture. Concentrated hydrochloric acid solution is then added to the second mixture to dissolve the third mixture again, resulting in a stainless steel sample solution. The pH of the stainless steel sample solution is then adjusted to obtain a stainless steel sample solution having a predetermined pH value.

[0072] In the above embodiment, in order to achieve faster dissolution, the mixed acid solution needs to be heated when dissolving the stainless steel sample. At the same time, when the hydrochloric acid solution is added to the second mixture for dissolution, it can also be heated until a clear and transparent stainless steel sample solution is obtained.

[0073] S6, obtaining the cadmium content in the stainless steel sample according to the cadmium element standard curve.

[0074] As an optional embodiment, the mixed acid includes concentrated nitric acid, concentrated hydrochloric acid and hydrofluoric acid.

[0075] In the above embodiment, concentrated nitric acid, concentrated hydrochloric acid and hydrofluoric acid are selected as the mixed acid to dissolve the stainless steel sample. The reason is that the combination of concentrated nitric acid and concentrated hydrochloric acid can dissolve the stainless steel sample. After adding hydrofluoric acid, it forms fluorine silicon compound with silicon in the sample, which can better dissolve the sample.

[0076] As an optional embodiment, the volume ratio of concentrated nitric acid, concentrated hydrochloric acid and hydrofluoric acid in the mixed acid is 2-3:10-15:1-2.

[0077] In the above embodiment, the volume ratio of concentrated nitric acid, concentrated hydrochloric acid and hydrofluoric acid in the mixed acid is controlled to be 2-3:10-15:1-2 because, usually, the ratio of concentrated nitric acid to concentrated hydrochloric acid when dissolving stainless steel is 1:3. However, in the present embodiment, the volume ratio of nitric acid is controlled to be less than 1:3 in order to prevent the nitrogen oxides generated after dissolution from being not completely driven away, which may affect the solubility of subsequent precipitation. At the same time, a small amount of hydrofluoric acid is added to react with silicon in the sample to form fluorosilicic acid, which is then heated to volatilize and remove silicon, thereby preventing the occurrence of silicic acid precipitation and achieving a better dissolution effect.

[0078] For example, the ratio of concentrated nitric acid, concentrated hydrochloric acid and hydrofluoric acid may be 2:10:1.

[0079] As an optional embodiment, the role of perchloric acid is to remove nitrogen oxides and hydrofluoric acid. The principle is that the boiling point of perchloric acid is 203°C. By heating and emitting perchloric acid smoke, low-boiling-point hydrofluoric acid and nitric acid substances can be removed. In order to ensure that hydrofluoric acid and nitric acid substances are completely removed, the added amount of perchloric acid is about twice the volume of concentrated nitric acid compared with nitric acid.

[0080] As an optional embodiment, adjusting the pH of the third mixture containing the hydrochloric acid solution to obtain a stainless steel sample solution with a set pH value specifically includes:

[0081] adding concentrated aqueous ammonia dropwise to the third mixture containing the hydrochloric acid solution until the precipitation no longer increases, to obtain a fourth mixture;

[0082] An acetic acid-ammonium acetate buffer solution is added to the fourth mixture to obtain a stainless steel sample solution with a set pH value. In the above embodiment, concentrated ammonia water is added dropwise to the third mixture containing the hydrochloric acid solution. Iron is present in the sample solution, and the addition of concentrated ammonia water can generate an iron hydroxide precipitate. When the Fe(OH)3 precipitate appears, the solution pH is about 5.0. When the Fe(OH)3 precipitate no longer increases, the solution pH is close to 6.0. Then, an acetic acid-ammonium acetate buffer solution (pH=6.0) is added to stabilize the solution pH and prevent the solution pH from changing with the addition of lead acetate and affecting the solubility of the precipitate. The above adjustment method is simple, the pH is more stable, and it is convenient to generate a more stable lead molybdate precipitate.

[0083] In the above embodiment, the pH value of the solution is controlled to be approximately 6.0 because the solubility of lead molybdate is appropriate at this pH. If the pH is too low, the solubility of lead molybdate increases, while if the pH is too high, lead hydroxide precipitation is likely to occur. Both of these results in incomplete precipitation of lead molybdate and inability to completely remove the molybdenum element in the solution.

[0084] As an optional embodiment, adding a lead acetate solution to the stainless steel sample solution to generate a lead molybdate precipitate to obtain a first mixture containing the lead molybdate precipitate specifically comprises:

[0085] adding lead acetate solution to the stainless steel sample solution;

[0086] heating the stainless steel sample solution containing the lead acetate solution to a first preset temperature;

[0087] Insulating the stainless steel sample solution containing the lead acetate solution under the first preset temperature and preset time conditions;

[0088] After the heat preservation is completed, the stainless steel sample solution containing the lead acetate solution is cooled to room temperature to obtain a first mixture containing lead molybdate precipitate.

[0089] In the above embodiment, the lead acetate solution is added to the stainless steel sample solution to generate a lead molybdate precipitate. The heating process accelerates the precipitation rate, and the purpose of holding the solution at this temperature for a period of time is to age the precipitate and increase the grain size, thereby fully precipitating the lead molybdate and facilitating subsequent separation. After the holding period, the stainless steel sample solution containing the lead acetate solution is cooled to room temperature to obtain a first mixture containing the lead molybdate precipitate, thereby preventing temperature changes from affecting the subsequent volume setting process.

[0090] As an optional implementation manner, the first preset temperature is 80° C. to 100° C., and the preset time is 0.8 h to 1.2 h.

[0091] In the above embodiment, during the heating and insulation process of the stainless steel sample solution containing the lead acetate solution, in order to maintain a high temperature to improve the efficiency of precipitation aging, it is also necessary to prevent the solution from splashing and not boiling. Therefore, the preset heating temperature is controlled to be 80℃~100℃. Exemplarily, the first preset temperature can be 80℃, 85℃, 90℃, 100℃; the preset insulation time can be 0.8h, 0.9h, 1.0h, 1.1h, 1.2h

[0092] As an optional embodiment, before the volume of the first mixture is fixed to obtain the sample mixture to be tested, the method further includes: adding acetic acid-ammonium acetate buffer solution to the mixture to obtain the first mixture with the set pH value.

[0093] In the above embodiment, acetic acid-ammonium acetate buffer solution is added to the mixture before volume adjustment in order to ensure the pH of the mixture and prevent the lead molybdate precipitate from changing.

[0094] As an optional embodiment, the method of performing solid-liquid separation on the sample mixture to be tested is dry filtration separation.

[0095] In the above embodiment, the dry filtration method can quickly separate the solution to be detected, reducing the time for precipitation, filtration and washing.

[0096] As an optional embodiment, preparing a series of concentration solutions of cadmium element specifically includes: taking n volumetric flasks, and accurately adding different volumes of cadmium standard solution of specific concentration into each volumetric flask.

[0097] In the above embodiment, the volumetric flasks for the series of concentration solutions are the same as the volumetric flasks used to determine the volume of the sample mixture to be tested. The concentration of the cadmium standard solution is 0.50 μg / mL.

[0098] As an optional embodiment, the cadmium element concentration series solution includes an equal amount of acetic acid-ammonium acetate buffer solution to ensure that the composition of the standard curve solution is as consistent as possible with the composition of the sample solution to be tested, reduce the matrix difference between the cadmium element standard curve solution and the sample solution, and eliminate the matrix effect during instrument analysis.

[0099] As an optional embodiment, inductively coupled plasma mass spectrometry is used to determine the cadmium content in a series of concentration solutions and the filtrate of the sample to be tested.

[0100] In the above embodiment, ICP-MS has significant advantages in determining cadmium content, such as high sensitivity, wide linear range, simultaneous analysis of multiple elements, high precision and accuracy, and is an ideal choice for trace and ultra-trace element analysis.

[0101] In each of the above embodiments, all reagents used are GR standards.

[0102] As an optional implementation, the stainless steel is 316 stainless steel.

[0103] The present application is further described below with reference to specific examples. Experimental methods in the following examples where specific conditions are not specified are generally measured in accordance with national / industry standards. If there are no corresponding national / industry standards, the methods are carried out in accordance with commonly used international standards, conventional conditions, or conditions recommended by the manufacturer.

[0104] Example

[0105] This embodiment provides a method for determining the trace cadmium content in stainless steel, wherein the stainless steel sample to be tested is GSBH40128-97, and the method comprises the following steps:

[0106] S1, accurately weigh 0.1g of stainless steel sample to the nearest 0.0001g and place it in a polytetrafluoroethylene beaker;

[0107] S2, add 5-10 mL of ultrapure water, 1 mL of concentrated nitric acid (GR), 5 mL of concentrated hydrochloric acid (GR), and 0.5 mL of hydrofluoric acid (GR) to a beaker, respectively, and place the beaker on a hot plate and heat at low temperature until the sample reacts completely to obtain a second mixture;

[0108] S3, adding 2 mL of perchloric acid (GR) to the second mixture in the beaker and heating until fuming, and then continuing to heat until nearly dry to drive off nitrogen oxides and hydrofluoric acid in the beaker, to obtain a third mixture.

[0109] S4. Remove the third mixture, add 3 mL of concentrated hydrochloric acid (GR) and a small amount of ultrapure water thereto, heat to dissolve the salts until the solution is clear and transparent, and there is no residue in the beaker, then allow the solution to cool naturally to room temperature to obtain a stainless steel sample solution.

[0110] S5, adding concentrated aqueous ammonia (GR) dropwise to the stainless steel sample solution until Fe(OH)3 precipitation no longer increases, and adding 5 mL of acetic acid-ammonium acetate buffer solution with a pH of 6.0 to adjust the pH of the stainless steel sample solution to 6.0;

[0111] S6, adding 3 mL of a 10% lead acetate solution dropwise thereto, heating to 80-100° C. and keeping the temperature for 1 hour, and then cooling to room temperature to obtain a first mixture containing a lead molybdate precipitate;

[0112] S7, add 15 mL of acetic acid-ammonium acetate buffer solution (pH=6.0) to the first mixture, dilute to a 200 mL volumetric flask, mix well, and dry filter using slow filter paper before analysis to obtain a sample solution to be tested.

[0113] S8, prepare standard curve solution: take 6 200mL volumetric flasks, accurately add 0mL (i.e., blank solution), 0.50mL, 1.00mL, 3.00mL, 5.00mL, and 10.00mL of cadmium standard solution with a concentration of 0.50μg / mL to 6 volumetric flasks; add 20mL of acetic acid-ammonium acetate buffer solution with a pH of 6.0 to each volumetric flask. After the addition of the standard solution is completed, add ultrapure water to the 6 volumetric flasks to the volumetric flask scale line to make up to 200mL, shake well, and wait for testing.

[0114] S9, use inductively coupled plasma mass spectrometry to measure the standard curve solution and draw the standard curve; the laboratory temperature during the test is 25 ° C, the room temperature fluctuation does not exceed 2 ° C within two hours, and the humidity is controlled below 60%; the purity of the argon gas used in the instrument analysis is ≥ 99.9995% and the gas quality is stable with small fluctuations. 103 Rh was used as the internal standard element, the internal standard element configuration was 20 μg / L, and the cadmium isotope was selected as " 114Cd”.

[0115] S10, using inductively coupled plasma mass spectrometry to detect the cadmium concentration in the sample solution to be tested, to obtain the concentration c, and then using the formula The cadmium content in the stainless steel sample was calculated, where c in the formula is the cadmium concentration in the sample solution to be tested using an inductively coupled plasma mass spectrometer, V is the constant volume, and m is the mass of the stainless steel sample. The final calculated cadmium content in the stainless steel sample is 0.000011%.

[0116] Comparative Example 1

[0117] This comparative example provides a method for determining the cadmium content in stainless steel. The stainless steel sample in the method is consistent with the sample in the embodiment, except that step S5 is omitted. The cadmium content obtained in the final test is 0.00307%, which is higher than the data in Example 1. The reason is that the pH value in the sample solution is not guaranteed to be stable at the set value, resulting in high solubility of the lead molybdate solution precipitate and the presence of molybdenum in the test solution, which affects the test results.

[0118] Comparative Example 2

[0119] This comparative example provides a method for determining the cadmium content in stainless steel. The stainless steel sample in the method is consistent with the sample in the embodiment, except that steps S3 and S4 are omitted. The final cadmium content obtained by the test is 0.000023%, which is higher than the data in Example 1. The reason is that nitrogen oxides increase the solubility of lead molybdate precipitates, and the test solution contains molybdenum, which affects the test results.

[0120] Comparative Example 3

[0121] This comparative example provides a method for determining the cadmium content in stainless steel. The stainless steel sample in the method is consistent with the sample in the embodiment, except that step S6 is omitted. The final cadmium content obtained by the test is 0.000036%, which is higher than the data in Example 1. The reason is that under acidic conditions, the positively charged surface of the iron hydroxide precipitate adsorbs most of the molybdate in the solution. However, the adsorption force is not strong enough, resulting in a small amount of molybdate being free in the solution, thereby affecting the test results.

[0122] In summary, the method for determining cadmium in stainless steel provided in this application has at least the following advantages:

[0123] 1. Eliminate the interference of molybdenum on cadmium by precipitation separation, without the need for special instruments, and the method has a wide range of applications;

[0124] 2. The method of heating and emitting perchloric acid fumes can quickly remove nitrogen oxides and eliminate the effect of nitrogen oxides on the solubility of precipitation;

[0125] 3. When adjusting the pH value of the solution, add concentrated ammonia water until the precipitation of iron hydroxide no longer increases. At this time, the pH value of the solution is about 5. Then add acetic acid-ammonium acetate buffer solution (pH = 6.0). The adjustment method is simpler and the pH is more stable.

[0126] 4. The solution to be tested can be quickly separated by dry filtration, reducing the time for precipitation, filtration and washing.

[0127] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but rather is intended to conform to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for determining trace cadmium content in stainless steel, wherein the stainless steel contains molybdenum and cadmium, comprising the following steps: obtaining a stainless steel sample solution having a set pH value; adding a lead acetate solution to the stainless steel sample solution to generate a lead molybdate precipitate, thereby obtaining a first mixture containing the lead molybdate precipitate; The first mixture is fixed to volume to obtain a sample mixture to be tested; Performing solid-liquid separation on the sample mixture to obtain a sample solution; preparing a series of concentration solutions of the cadmium element, and drawing a cadmium element standard curve based on the series of concentration solutions; The cadmium content in the stainless steel sample is obtained according to the cadmium element standard curve.

2. The determination method according to claim 1, wherein the accurately weighing the stainless steel sample and obtaining the stainless steel sample solution having a set pH value specifically comprises: Accurately weigh stainless steel samples; dissolving the stainless steel sample with a mixed acid solution to obtain a second mixture; adding perchloric acid to the second mixture, and heating the second mixture containing the perchloric acid to obtain a third mixture; adding a hydrochloric acid solution to the third mixture; The pH of the third mixture containing the hydrochloric acid solution is adjusted to obtain a stainless steel sample solution with a set pH value.

3. The assay method according to claim 2, wherein the mixed acid comprises concentrated nitric acid, concentrated hydrochloric acid and hydrofluoric acid.

4. According to the assay method described in claim 3, the volume ratio of concentrated nitric acid, concentrated hydrochloric acid and hydrofluoric acid in the mixed acid is 2-3:10-15:1-2.

5. The determination method according to claim 2, wherein adjusting the pH of the third mixture containing the hydrochloric acid solution to obtain the stainless steel sample solution having a set pH value specifically comprises: adding concentrated aqueous ammonia dropwise to the third mixture containing the hydrochloric acid solution until the precipitation no longer increases, to obtain a fourth mixture; An acetic acid-ammonium acetate buffer solution is added to the fourth mixture to obtain a stainless steel sample solution with a set pH value.

6. The determination method according to claim 1, wherein the step of adding a lead acetate solution to the stainless steel sample solution to generate a lead molybdate precipitate to obtain a first mixture containing the lead molybdate precipitate comprises: adding lead acetate solution to the stainless steel sample solution; heating the stainless steel sample solution containing the lead acetate solution to a first preset temperature; Insulating the stainless steel sample solution containing the lead acetate solution under the first preset temperature and preset time conditions; After the heat preservation is completed, the stainless steel sample solution containing the lead acetate solution is cooled to room temperature to obtain a first mixture containing lead molybdate precipitate. The measuring method according to claim 6 , wherein the first preset temperature is 80° C. to 100° C., and the preset time is 0.8 h to 1.2 h.

8. The assay method according to claim 1, wherein the first mixture is constant to volume to obtain a sample mixture to be tested, further comprising: An acetic acid-ammonium acetate buffer solution is added to the mixture to obtain a first mixture having the set pH value. 9 . The determination method according to claim 1 , wherein the series of concentration solutions of cadmium element have the set pH value.

10. The determination method according to claim 1, wherein the cadmium content in the series of concentration solutions of cadmium element and the sample solution to be tested is determined by inductively coupled plasma mass spectrometry.

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