A method for determining the platinum content in platinum jewelry by automatic potentiometric titration

Abstract

This invention provides an automated potentiometric titration method for determining the platinum content in platinum jewelry, belonging to the field of precious metal analysis and detection technology. The method mainly includes: dissolving the platinum jewelry sample in aqua regia and using a separating reagent to precipitate and separate interfering precious metals such as palladium, gold, and silver. Subsequently, the sample is passed through a strongly basic anion exchange resin column, where platinum is selectively adsorbed as chloroplatinate complex anions to obtain a purified platinum solution. The platinum content is calculated using a back titration method. This method integrates interfering element separation, ion exchange purification, back titration, and automated potentiometric detection technologies, and optimizes the electrode system. This method has the advantages of high accuracy, good precision, strong anti-interference ability, and relatively simple and reliable operation, and is suitable for the accurate determination of platinum content in platinum jewelry and platinum alloys of various purities such as Pt900, Pt950, and Pt990.

Description

Technical Field

[0001] This invention relates to the field of precious metal analysis and testing technology, specifically to an automatic potentiometric titration method for determining the platinum content in platinum jewelry. Background Technology

[0002] Platinum jewelry, with its high hardness, strong metallic luster, and pure white color that resists fading, along with its enduring and pure emotional connotations, represents high-end jewelry. The mainstream products on the market are primarily in purity grades such as Pt900, Pt950, and Pt990. To optimize the craftsmanship and durability of jewelry, metals such as palladium, rhodium, and copper are added to platinum during production to form platinum-based alloys. Platinum content, as a core indicator determining the quality and value of platinum jewelry, is directly related to product purity, quality control, craftsmanship evaluation, and trade pricing. Therefore, conducting rapid, accurate, and reliable testing of the platinum content in platinum jewelry is a crucial requirement for protecting consumer rights and promoting high-quality development in the industry.

[0003] Currently, there are four main methods for detecting platinum content: ammonium chloroplatinate gravimetric method, fire assay, X-ray fluorescence spectrometry, and inductively coupled plasma atomic emission spectrometry. Each method has significant limitations and is difficult to meet the precise detection requirements of high-purity major elements in platinum jewelry. The ammonium chloroplatinate gravimetric method, as a conventional method, has a lengthy procedure and strict operational requirements. It is prone to deviations due to factors such as the difficulty of precipitation treatment, co-precipitation of impurities, and changes in platinum valence state. It is highly dependent on the sample properties and the professional expertise of the operator. The fire assay is more suitable for the enrichment of trace precious metals. It needs to be combined with other instruments to complete the determination. Moreover, the correction process for common impurities in platinum jewelry such as gold, palladium, rhodium, and iridium is complicated and has high uncertainty, making direct determination unsuitable.

[0004] While X-ray fluorescence spectrometry is a non-destructive testing method widely used for preliminary screening of jewelry, its results are easily affected by sample surface condition, inter-elemental interference, and the matching degree of standard samples. Its accuracy cannot meet legal testing requirements, allowing only semi-quantitative analysis. Furthermore, this method can only detect a 0-20 μm thickness region on the sample surface, failing to reflect the true platinum content within the sample and posing a risk of distorted results. Inductively coupled plasma atomic emission spectrometry (ICP-AES) excels at detecting trace impurities. However, when used for determining high platinum content in platinum jewelry, the sample needs to be diluted thousands or even tens of thousands of times. This dilution significantly amplifies errors, and high-concentration platinum matrices can easily cause changes in plasma excitation characteristics, decreased atomization efficiency, and enhanced background radiation. Even with internal standard methods, it is difficult to completely correct for matrix effects, making it challenging to guarantee measurement accuracy.

[0005] Existing detection methods suffer from shortcomings in terms of ease of operation, interference resistance, precision, and accuracy, posing numerous challenges to the accurate determination of platinum content in platinum jewelry. Titration, in principle, is suitable for determining the percentage content of major elements, offering advantages such as relative simplicity and good quantification. Furthermore, automated potentiometric titrators, with their higher resolution and sensitivity, can accurately determine the titration endpoint by observing changes in electrode potential during the titration process, providing a technical path to overcome the shortcomings of existing methods. Therefore, developing a platinum content detection method based on automated potentiometric titration, combined with ion exchange and back titration techniques, and adapted to the characteristics of the platinum jewelry matrix, to achieve highly accurate and interference-resistant platinum content determination, has become an urgent need in this field. Summary of the Invention

[0006] In view of the technical problems existing in the background art, the present invention provides an automatic potentiometric titration method for determining the platinum content in platinum jewelry.

[0007] This invention provides an automatic potentiometric titration method for determining the platinum content in platinum jewelry, comprising the following steps:

[0008] S1. Sample dissolution and preliminary impurity separation: Dissolve the platinum jewelry sample in aqua regia, evaporate and repeatedly add hydrochloric acid to remove nitric acid, and obtain a platinum-containing solution; add a separation reagent to the platinum-containing solution to precipitate and separate at least one of palladium, gold and silver, and obtain a preliminarily purified platinum-containing filtrate.

[0009] S2, Ion exchange adsorption and elution: The platinum-containing filtrate obtained in step S1 is passed through a strong basic anion exchange resin column, so that platinum is selectively adsorbed in the form of hexachloroplatinate ions. After washing with low-concentration hydrochloric acid to remove the unadsorbed base metal cations, it is eluted with high-concentration hydrochloric acid, and the purified platinum eluent is collected.

[0010] S3. Back titration: Under inert gas protection, the platinum eluent obtained in step S2 is added to an excess of stannous chloride standard solution to reduce tetravalent platinum to divalent platinum; the remaining stannous chloride after reduction is then subjected to automatic potentiometric titration with cerium sulfate standard solution, and the volume of cerium sulfate standard solution consumed is recorded. V 1 Simultaneously, record the volume of cerium sulfate standard solution consumed in the blank titration. V 0 ;

[0011] S4. Platinum content calculation: The platinum content is calculated based on the concentration of the cerium sulfate standard solution and the difference between the sample titration volume and the blank titration volume.

[0012] As a further improvement of the present invention, the formula for calculating the platinum content in step S4 is as follows:

[0013] ;

[0014] In the formula:

[0015] w This refers to the mass fraction of platinum in platinum jewelry;

[0016] C This represents the concentration of the cerium sulfate standard solution, expressed in mol / L.

[0017] V 0 This represents the volume of cerium sulfate consumed in the blank test, in mL.

[0018] V 1 The volume of cerium sulfate consumed in titrating the sample, in mL;

[0019] M Pt The molar mass of platinum is 195.08, in g / mol.

[0020] m represents the sample mass, expressed in grams.

[0021] As a further improvement of the present invention, in step S2, the strongly basic anion exchange resin is a quaternary ammonium-based strongly basic anion exchange resin with a polystyrene-divinylbenzene backbone.

[0022] As a further improvement of the present invention, in step S3, the automatic potentiometric titration uses a combined gold ring electrode as the indicator electrode and a dual salt bridge reference electrode as the reference electrode.

[0023] As a further improvement of the present invention, in step S1, the separation reagent includes sulfur dioxide and / or dimethylglyoxime, used to precipitate and separate gold and palladium respectively.

[0024] As a further improvement of the present invention, in step S2, the platinum-containing filtrate is adjusted to a specific hydrochloric acid concentration in a hydrochloric acid medium before ion exchange adsorption is performed. The hydrochloric acid medium is a low-concentration hydrochloric acid with a concentration of 1-3 mol / L; the high-concentration hydrochloric acid is a hydrochloric acid solution with a concentration of 4-8 mol / L.

[0025] As a further improvement of the present invention, in step S3, the inert gas is high-purity nitrogen, and the time of introduction before pre-reduction is 5-10 minutes, and the hydrochloric acid medium is controlled at 1-3 mol / L; the mass concentration of stannous chloride solution is 8-12%, and the amount added is based on the solution color changing from light yellow to stable reddish-brown, and then an excess of 2-5 mL is added.

[0026] As a further improvement of the present invention, in step S2, the flow rate of the ion exchange column is 0.5-2 mL / min, the washing flow rate is 1-3 mL / min, and the elution flow rate is 0.5-2 mL / min.

[0027] As a further improvement of the present invention, before step S1, a resin pretreatment and column packing pretreatment step are also included.

[0028] This invention provides a method specifically for determining the platinum content in platinum jewelry. Based on two core mechanisms—ion exchange separation and redox potentiometric titration—it is the first to use ion exchange resin for the separation and purification of platinum in platinum jewelry. Accurate determination of platinum content is achieved through optimized sample pretreatment processes, accurate separation and purification, masking of interfering elements, inert gas isolation, improved electrode systems, and precise control of the titration unit. The specific inventive mechanism is as follows:

[0029] Precious metal separation technology: Platinum jewelry (Pt900, Pt950, Pt990) usually contains precious metal impurities such as gold, silver, palladium, rhodium, iridium, and ruthenium. After the sample is completely dissolved in aqua regia, the solution is evaporated to near dryness with concentrated hydrochloric acid multiple times to completely remove nitrate ions. It is then leached with 1-3 mol / L hydrochloric acid to obtain a chloroplatinic acid solution. Dimethylglyoxime ethanol solution is added as a reagent, and finally sulfur dioxide gas is passed through for 10-30 min. During this process, gold, silver, palladium, rhodium, iridium, and ruthenium are effectively separated. Rhodium, iridium, and ruthenium are not easily separated from the chloroplatinic acid solution by precipitation because they are not easily dissolved in aqua regia. Gold, silver, and palladium undergo the following reduction and precipitation reactions (see formulas (1)-(3)) and are finally separated from the chloroplatinic acid solution by precipitation. This completely solves the problem of the influence of gold, silver, palladium, rhodium, iridium, and ruthenium on the accuracy of the results.

[0030] ···(1)

[0031] Ag + +Cl - →AgCl↓··········(2)

[0032] Pd 2+ +2H2Dm→Pd(HDm)2↓+2H + (H2Dm represents dimethylglyoxime (C4H8N2O2)) (3)

[0033] Ion exchange technology: Utilizing the strongly basic anion Cl- of the polystyrene-divinylbenzene framework. - This type of ion exchange resin (D201 macroporous resin) has a three-dimensional network structure. This structure provides a supporting carrier and increases the specific surface area of ​​the macroporous structure, enabling the large-volume complexation of anions [PtCl6] in the solution. 2- (Hexachloroplatinate) diffuses smoothly into the active sites inside the resin, improving adsorption efficiency and capacity. Its functional group is a quaternary ammonium group (-CH2N). +(CH3)3), this group carries a permanent positive charge and can bind to negatively charged exchangeable ions through electrostatic attraction, and can strongly adsorb anions (Cl) in solution. - Platinum (in the form of [PtCl6] resin) in a hydrochloric acid medium of approximately 1-3 mol / L 2- The anionic form of [PtCl6] is stable; when the sample solution passes through the resin column, [PtCl6]... 2- Selectively adsorbed on resin ([RN) + (CH3)3]Cl - On resins representing the chloride form (see equation (4)), since resins have different affinities for different anions, in hydrochloric acid medium, the affinity of strongly basic anion exchange resins for anions follows the Hoffmann selectivity law, that is, the higher the ion charge number and the larger the ion radius, the stronger the electrostatic attraction and van der Waals force with the quaternary ammonium groups of the resin, such as [PtCl6]. 2- Such high-valence, large-volume complex anions have a much greater affinity than Cl. - Therefore, it can be quantitatively and strongly adsorbed, while base metal impurity ions (such as Cu) commonly found in platinum jewelry... 2+ Zn 2+ Ni 2+ Co 2+ Al 3+ The presence of cations (such as Cu) in the resin does not lead to adsorption because the active sites of the resin only carry a positive charge and can only bind to anions through electrostatic interactions, having no adsorption capacity for cations. As the resin flows out with the washing liquid, platinum is completely separated from most interfering elements, thus completely eliminating base metal impurity ions (such as Cu). 2+ Zn 2+ Ni 2+ Co 2+ Al 3+ The effect of cationic form on the accuracy of results is shown in the reaction principle diagram. Figure 1 As shown.

[0034] 2[RN + (CH3)3]Cl - +[PtCl6] 2- →[RN + [(CH3)3]2[PtCl6] 2- +2Cl - ··(4)

[0035] Back titration technique: This method involves separating and purifying [PtCl6]. 2- The solution was reduced to [PtCl4] by adding stannous chloride reducing agent to a 1-3 mol / L hydrochloric acid medium. 2-(Divalent platinum) undergoes chemical reaction (5). The main reaction of this reaction is kinetically slow and stoichiometrically unstable, making direct titration unsuitable for quantitative analysis. The slow reaction kinetics are due to [PtCl6]. 2- The stable complex anion with an octahedral configuration has a stable electronic configuration with the central platinum ion, and is compatible with Sn. 2+ The electron transfer process is hindered, resulting in a long time to reach equilibrium. Direct titration would lead to a tailing or blurring of the endpoint due to incomplete reaction, making accurate endpoint determination impossible. The stoichiometric relationship is unstable because the stoichiometric ratio (molar ratio) is easily affected by factors such as hydrochloric acid concentration, temperature, and chloride ion concentration. Excessive hydrochloric acid concentration enhances stability and reduces the reaction rate, while low temperature further inhibits electron transfer, causing the actual amount consumed to deviate from the theoretical value, making direct titration ineffective for calculating the platinum content. Therefore, a back titration method is used, employing an excess addition followed by precise back titration. The excess stannous chloride is replaced with cerium sulfate (Ce). 4+ The standard solution is back-titrated, and chemical reaction (6) occurs. An excess of stannous chloride standard solution is accurately added to the purified solution. Even if the main reaction kinetics are slow and the conditions are sensitive, the excess solution can still be completely reduced to [PtCl4]. 2- This completely eliminates the problem of incomplete reaction. Then, the remaining reducing agent is back-titrated with a strong oxidizing agent, using cerium sulfate (Ce) which is chemically stable and has a well-defined stoichiometric relationship. 4+ The standard solution was used to titrate the remaining Sn after the first step of the reaction. 2+ Ce 4+ With Sn 2+ The reaction is rapid and complete, and is not significantly affected by the acidity of the medium (1-3 mol / L hydrochloric acid). It solves the problem that the direct reduction reaction of platinum(IV) with stannous chloride has slow kinetics, and the stoichiometric relationship can change due to factors such as acidity, temperature, and chloride ion concentration, potentially leading to incomplete reaction. Direct titration can result in ambiguous endpoints and biased results. By employing back titration technology, the remaining stannous chloride is titrated with stable, stoichiometrically defined cerium sulfate. This transforms a difficult-to-control reaction with unclear stoichiometry into a rapid and complete titration process with a clear stoichiometric relationship, thus significantly improving analytical accuracy.

[0036] [PtCl6] 2− +Sn 2+ →[PtCl4] 2 −+Sn 4+ +2Cl − ·····(5)

[0037] Sn 2+ +2Ce 4+ →Sn 4+ +2Ce3+ ········(6)

[0038] Systematic error compensation technology: A back titration blank correction method is adopted, based on the principles of "equivalent cancellation" and "apparent stoichiometric coefficient integration." This effectively eliminates systematic errors. An equal amount of SnCl2 is added to a platinum-free base solution, and the same pretreatment, operating procedures, and titration conditions as the sample are performed. This effectively solves the following three drawbacks: First, interference from reagent and solvent impurities. Reagents, acidic media (such as hydrochloric acid), and distilled water inevitably contain trace amounts of reducing impurities (Fe). 2 + Mn 2+ Impurities such as organic matter can consume titrant, leading to an artificially high titration volume; secondly, Sn... 2+ The decomposition and oxidation loss of the substance can easily lead to oxidation by dissolved oxygen in the solution or oxygen in the air. Under high temperature conditions, it may hydrolyze to form basic tin chloride precipitate, resulting in a reduction in the effective reducing dose. Thirdly, there is the deviation between the theoretical stoichiometric ratio and the actual reaction. In actual titration, due to factors such as the color change point of the indicator and the titration rate, there are slight differences between the actual stoichiometric ratio and the theoretical value. If the theoretical stoichiometric ratio is used for calculation, a systematic deviation will be introduced.

[0039] This back titration method directly reflects the equivalent Ce of SnCl2 reacting with platinum. 4+ Volume, without prior knowledge of the precise theoretical stoichiometric ratio between Pt:Sn:Ce, by matching the blank group and the sample group under full conditions to offset the systematic errors of non-target reactions, and by incorporating the apparent stoichiometric coefficients of the actual reaction into the quantitative system through pure platinum calibration, the accurate platinum measurement can be achieved without relying on the theoretical stoichiometric ratio. This technology is a key means to ensure the accuracy of results in the tin reduction-cerium titration method.

[0040] Automatic potentiometric titration technology: To obtain a sharp and reliable titration endpoint, two key techniques were employed: First, precise potentiometric titration control technology was used, controlling the potential resolution to 0.1 mV and the volume resolution to 0.001 mL, ensuring sufficiently high accuracy, significantly superior to the traditional burette titration method using color identification. Second, a full-process inert gas protection technology was used, introducing high-purity nitrogen to prevent the oxidation of certain reduced substances or the solution itself by air (oxygen) at the top of the container, thus avoiding the oxidation and inactivation of stannous chloride. Since the method uses back titration to add excess stannous chloride, if stannous chloride becomes ineffective, the amount added must be increased, leading to an overestimation of the result. These two methods significantly improve the precision and accuracy of the method, avoiding the errors associated with traditional manual color titration. Direct titration of Pt(IV) with SnCl2 suffers from a gradual potential change and indistinct abrupt change, while the reaction between cerium sulfate and stannous chloride (2Ce) addresses this issue. 4+ +Sn 2+ →2Ce3+ +Sn 4+ This rapid, quantitative reaction with a large potential jump is ideal for potentiometric titration. The instrument can identify the endpoint very accurately, and the endpoint determination is extremely accurate and repeatable, eliminating subjective errors and significantly improving the precision (RSD) of the analytical results.

[0041] Electrode selection optimization technology: Potentiometric titration typically uses a platinum electrode as the indicator electrode and a calomel electrode as the reference electrode. This combination is suitable for titrating most elements. This study employs a gold ring electrode + double salt bridge reference electrode configuration, replacing the platinum electrode with a gold ring electrode. Since the titration solution contains a large amount of chloride ions and acid, the gold electrode exhibits higher inertness in chloride-containing and acidic media and at higher potentials, preventing passivation due to oxide film formation on the platinum electrode surface or adsorption of large amounts of impurities leading to decreased sensitivity. It also solves the problems of platinum electrode overlap with the analyte, slight dissolution in the analyte, and charge transfer affecting the accuracy of the measurement results. The double salt bridge reference electrode replaces the single salt bridge structure. During titration, Cl... - Concentration may vary due to reaction and dilution; ions in the titrant are prone to diffusion and interference with the internal filling solution, leading to reference potential drift, especially in long-term titrations or high-Cl titrations. - At certain concentrations, the double salt bridge structure effectively isolates interfering ions (such as Cl-) in the titrant. - This ensures the long-term absolute stability of the reference potential, making the readings more reliable.

[0042] The beneficial effects of this invention are:

[0043] This invention addresses the shortcomings of traditional detection methods such as the ammonium chloroplatinate gravimetric method, fire assay, X-ray fluorescence spectrometry, and inductively coupled plasma atomic emission spectrometry by innovatively optimizing them. Through the integration of multiple technologies and precise control of process parameters, it achieves a comprehensive improvement in detection performance, operational practicality, and industry adaptability compared to traditional methods, producing significant and diverse beneficial effects, as detailed below:

[0044] 1. High detection accuracy and thorough interference elimination: A two-step separation strategy, combining precipitation to separate precious metal impurities such as gold, silver, palladium, rhodium, iridium, and ruthenium with ion exchange technology to separate base metal impurities such as copper, nickel, and zinc, eliminates the influence of most interfering elements on the titration reaction from the source, ensuring the specificity of the potentiometric titration reaction. At the same time, the accompanying back titration blank correction technology effectively compensates for systematic errors caused by reagent impurities, reducing agent loss, and deviations between theoretical and actual stoichiometric ratios, resulting in a high degree of agreement between the final measurement results and the standard values.

[0045] 2. Excellent precision and good reproducibility: The automatic potentiometric titrator determines the titration endpoint by the potential jump point, achieving precise control with a potential resolution of 0.1mV and a volume resolution of 0.001mL. This completely avoids the subjective bias and insensitive endpoint caused by color judgment in traditional visual titration. The high-purity nitrogen inert protection throughout the process further avoids the problem of reducing agent oxidation failure, resulting in extremely low relative standard deviation (RSD) for multiple parallel determinations of the same sample. The method precision and result reproducibility far exceed those of traditional detection methods.

[0046] 3. Wide range of applications and strong adaptability: Based on the core principle of chemical separation, this method does not rely on expensive standard sample matching, nor does it require the construction of complex matrix calibration models. It overcomes the technical limitations of traditional gravimetric methods, which have strict requirements on sample properties; X-ray fluorescence spectroscopy, which is greatly affected by sample surface conditions and inter-element interference; and ICP-OES, which is difficult to measure in high-concentration platinum matrices. It can be widely applied to platinum jewelry of different purity specifications such as Pt900, Pt950, and Pt990. At the same time, it can accurately measure complex platinum alloys containing multiple alloying elements such as palladium, rhodium, copper, and zinc. It is suitable for various testing needs such as statutory laboratory testing and quality control of jewelry manufacturing enterprises.

[0047] 4. Simple and efficient operation with significantly improved reliability: Compared with the lengthy process of multiple precipitation, filtration, and ignition in the ammonium chloroplatinate gravimetric method, and the complex calibration steps required by the fire assay method in conjunction with other instruments, this method optimizes the entire process from sample digestion to result calculation, with a high degree of automation and reduced manual operation. At the same time, the standardized operating procedure reduces the reliance on the operator's experience and subjective judgment, avoids the result deviation problem caused by improper manual operation in traditional methods, and greatly improves detection efficiency and operational reliability.

[0048] 5. Controllable consumable costs and moderate equipment requirements: The use of macroporous strong-base anion exchange resin as the core separation consumable significantly reduces the cost of testing consumables; the testing process only requires conventional instruments such as an automatic potentiometric titrator, without the need for large-scale precision instruments such as ICP-OES / ICP-MS, making the equipment investment cost more acceptable to various testing institutions, combining economy and practicality.

[0049] 6. Establishing standardized solutions to support the standardized development of the industry: This method creatively integrates and optimizes mature technologies such as ion exchange, back titration, and automatic potentiometric titration for the specific scenario of platinum content detection in platinum jewelry. It has formulated a standardized analytical method with full controllability from resin pretreatment, sample digestion, separation and purification to potentiometric titration and result calculation. This provides a reliable and unified testing basis for the determination of platinum jewelry purity and quality control, which is of great practical significance for promoting the standardization and high-quality development of the platinum jewelry industry.

[0050] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0051] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the present invention will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0052] Figure 1 This is a schematic diagram illustrating the principle of the ion exchange resin reaction for determining the platinum content in platinum jewelry provided by this invention.

[0053] Figure 2 This is a schematic diagram of the back titration process provided by the present invention. Detailed Implementation

[0054] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0056] In the description of the embodiments of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this invention, "multiple" means two or more, unless otherwise explicitly defined.

[0057] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0058] In the description of the embodiments of this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0059] In the description of the embodiments of the present invention, the term "multiple" refers to two or more (including two), similarly, "multiple groups" refers to two or more (including two groups), and "multiple pieces" refers to two or more (including two pieces).

[0060] In the description of the embodiments of the present invention, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0061] In the description of the embodiments of the present invention, unless otherwise explicitly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention according to the specific circumstances.

[0062] To address the problems of complex operation, numerous interferences, poor precision, and low accuracy associated with traditional detection methods, this invention provides an automated potentiometric titration method for determining the platinum content in platinum jewelry. This method integrates a series of separation, purification, quantification, compensation, and anti-interference techniques into a high-precision automated analysis system suitable for complex commercial samples, comprising the following steps:

[0063] S0, Resin Pretreatment and Column Packing: including swelling and purification, column packing, transformation and equilibration processes.

[0064] S1. Sample dissolution and preliminary impurity separation: Dissolve the platinum jewelry sample in aqua regia, evaporate and repeatedly add hydrochloric acid to remove nitric acid, and obtain a platinum-containing solution; add a separation reagent to the platinum-containing solution to precipitate and separate at least one of palladium, gold and silver, and obtain a platinum-containing filtrate with preliminary impurity removal.

[0065] S2. Ion exchange adsorption and elution: The platinum-containing filtrate obtained in step S1 is passed through a strongly basic anion exchange resin column, so that platinum is selectively adsorbed in the form of hexachloroplatinate ions. After washing with low-concentration hydrochloric acid to remove unadsorbed base metal cations, it is eluted with high-concentration hydrochloric acid, and the purified platinum eluent is collected.

[0066] S3, Back titration: Please refer to... Figure 2 As shown, under inert gas protection, excess stannous chloride standard solution was added to the platinum leaching solution obtained in step S2 to reduce tetravalent platinum to divalent platinum; the remaining stannous chloride after reduction was then subjected to automatic potentiometric titration with cerium sulfate standard solution, and the volume of cerium sulfate standard solution consumed was recorded. V 1 Simultaneously, record the volume of cerium sulfate standard solution consumed in the blank titration. V 0 .

[0067] S4. Platinum Content Calculation: The platinum content is calculated based on the concentration of the cerium sulfate standard solution and the difference between the sample titration volume and the blank titration volume. The formula for calculating the platinum content is as follows:

[0068] ;

[0069] In the formula:

[0070] C The concentration of the cerium sulfate standard solution is expressed in mol / L.

[0071] V 0 : Volume of cerium sulfate consumed in the blank test, in mL;

[0072] V 1 : The volume of cerium sulfate consumed in the titration of the sample, in mL;

[0073] M Pt The molar mass of platinum is 195.08 g / mol.

[0074] Examples 1-5

[0075] In Examples 1 to 5 of this invention, standard sample No. 4 of GSB04-3313-2019 was selected as the test sample, and its values ​​are shown in Table 1. The adsorption and impurity removal capabilities of five different ion exchange resins were investigated, including four polystyrene-divinylbenzene quaternary ammonium ion exchange resins (models 201×7, D201, AmberliteIRA-400, and Dowex1, respectively) and one sulfonic acid-based cationic ion exchange resin. The results are shown in Table 2. The specific process includes the following steps:

[0076] S0. Resin pretreatment and column packing:

[0077] S01. Swelling and purification: Soak 201 resin in ultrapure water for 24 hours to allow it to swell fully, soak it in ethanol for 2-3 hours to remove organic impurities, and then wash it with ultrapure water to remove the ethanol.

[0078] S02. Column Packing: Mix the treated resin with water and pour the slurry into the exchange column, allowing the resin to settle naturally and form a uniform, bubble-free resin bed. The height of the resin bed is approximately 2 / 3 of the column height.

[0079] S03, Transformation and Equilibrium: Pass the resin sequentially through the column with 2-3 column volumes of 1 mol / L NaOH solution, wash with ultrapure water until neutral, and then pass it through the column with 4-5 column volumes of 2 mol / L HCl solution to allow the resin to transition from OH- to HCl. - Type conversion to Cl - For the first type, equilibrate the resin with approximately 10-20 column volumes of 2 mol / L HCl at a slow flow rate (approximately 1 mL / min) until the pH of the effluent matches that of the incoming 2 mol / L HCl.

[0080] S1. Sample Dissolution and Preliminary Impurity Separation: The platinum jewelry sample was dissolved in aqua regia, evaporated, and hydrochloric acid was repeatedly added to remove nitric acid, yielding a platinum-containing solution. A separation reagent was added to the platinum-containing solution to precipitate and separate at least one of palladium, gold, and silver, yielding a preliminarily purified platinum-containing filtrate. Specifically:

[0081] Accurately weigh approximately 0.1-0.3 g (accurate to 0.0001 g) of the sample and place it in a 150 mL flask. Add 10-15 mL of aqua regia, cover with a watch glass, and heat in a fume hood at low temperature until the sample is completely dissolved. Evaporate the solution to near dryness, add 5 mL of concentrated hydrochloric acid, and evaporate again to near dryness. Repeat this "add hydrochloric acid-evaporate to dryness" operation 2-3 times to thoroughly remove nitric acid. Add 20 mL of 2 mol / L HCl for leaching, and purge with sulfur dioxide gas for 10-15 minutes to reduce the gold in the solution to elemental gold. Filter to separate, wash several times, and collect the filtrate in a beaker for later use.

[0082] S2. Ion Exchange Adsorption and Elution: The platinum-containing filtrate obtained in step S1 is passed through a strongly basic anion exchange resin column, allowing platinum to be selectively adsorbed as hexachloroplatinate ions. Unadsorbed base metal cations are then removed by washing with low-concentration hydrochloric acid, followed by elution with high-concentration hydrochloric acid. The purified platinum eluent is collected. (See also...) Figure 1 As shown, specifically:

[0083] S21. Adsorption column separation: Pass the liquid from the previous step through the equilibrated ion exchange column at a flow rate of 1 mL / min. Wash the beaker several times with a small amount of 2 mol / L HCl and load the washing solution onto the column. Wash the resin column with a large amount (about 150-200 mL) of 2 mol / L HCl at a flow rate of 2 mL / min. This step aims to thoroughly wash out all non-adsorbed base metal cations.

[0084] S22. Eluting Platinum: Use 50-80 mL of 6 mol / L HCl as the eluent to elute the resin at a flow rate of 1 mL / min. Collect the eluent in a clean beaker. This portion of the solution contains purified platinum and should exhibit the characteristic yellow color of chloroplatinic acid. After collection, evaporate and concentrate the eluent to approximately 10-15 mL on a low-temperature hot plate for titration.

[0085] S3, Back titration: Please refer to... Figure 2 As shown, under inert gas protection, excess stannous chloride standard solution was added to the platinum leaching solution obtained in step S2 to reduce tetravalent platinum to divalent platinum; the remaining stannous chloride after reduction was then subjected to automatic potentiometric titration with cerium sulfate standard solution, and the volume of cerium sulfate standard solution consumed was recorded. V 1 Simultaneously, record the volume of cerium sulfate standard solution consumed in the blank titration. V 0 Specifically:

[0086] S31. Pre-reduction of the test solution: Purge the concentrated platinum eluent with high-purity nitrogen gas for 5-10 minutes to remove dissolved oxygen. Under nitrogen protection, control the hydrochloric acid medium at 1-3 mol / L, and add 10% stannous chloride solution dropwise to the hot solution until the solution color changes from pale yellow to a stable reddish-brown, indicating that Pt(IV) has been quantitatively reduced to Pt(II). Add an excess of 2-3 mL. Continue to purge with protective gas and cool the solution to room temperature.

[0087] S32 Potentiometric Titration: Place the titration vessel on the titration stage, insert the cleaned combination gold ring electrode and double salt bridge, and select cerium sulfate as the standard solution. Begin the titration and record the potential-volume curve in real time. The potential jump point is the endpoint, and record the volume of cerium sulfate consumed, V1 (mL). Under the same conditions, perform the entire operation and titration using a platinum-free blank solution, and record the volume consumed in the blank. V 0 (mL).

[0088] S4. Platinum content calculation: The platinum content is calculated based on the concentration of the cerium sulfate standard solution and the difference between the sample titration volume and the blank titration volume.

[0089] Table 1 Standard Sample Values

[0090]

[0091] Table 2. Effect of different polystyrene-divinylbenzene ion exchange resins on the results.

[0092]

[0093] The results in Table 2 show that the low yield of 201×7 (domestic) in Example 1 was due to the difficulty in completely detaching platinum ions from the gel with 6 mol / L HCl after adsorption by the ion exchange resin. The high yield of TulsimerCH-95 (foreign) in Example 4 was due to the ineffective separation of other interfering elements, which interfered with the participation of cations in the titration reaction. The low yield of Dowex AG50W-X8 (foreign) in Example 5 was due to the presence of sulfonic acid-based cations, which prevented the complete adsorption of platinum ions by the ion exchange resin. The recovery rates of D201 (domestic) in Example 2 and AmberliteIRA-400 (foreign) in Example 3 met the requirements. However, since AmberliteIRA-400 requires multiple and lengthy detachments and is too expensive, D201 (domestic) ion exchange resin in Example 2 was chosen because it meets the requirements for precision and accuracy.

[0094] Examples 6-9

[0095] Examples 6 to 9 selected standard sample No. 4 of GSB04-3313-2019 as the test sample, and its values ​​are shown in Table 1. The procedures in Example 2 were followed, except that the effects of the concentration of the adsorption medium of the ion adsorption resin (0.5 mol / L, 1 mol / L, 3 mol / L, and 4 mol / L) on the results were investigated. The concentration of the adsorption medium directly affects [PtCl6]. 2- The results of whether the resin can effectively adsorb the elements and whether other interfering elements can be effectively separated are shown in Table 3.

[0096] Table 3. Effect of adsorption medium concentration on results

[0097]

[0098] Based on the data from Example 2, the results in Table 3 indicate that when the concentration of hydrochloric acid in the adsorption medium is below 2 mol / L, the chloride ion concentration is too low to provide stable chloride ions for the formation of stable [PtCl6] from platinum. 2- Consequently, it cannot be completely adsorbed by the quaternary ammonium strong base anion D201, leading to lower results. Furthermore, when the concentration of hydrochloric acid in the adsorption medium is higher than 2 mol / L, some platinum ions adsorbed by the resin are released into the solution. This is because the release solution is also hydrochloric acid at a concentration of 6 mol / L, indicating that a high concentration of hydrochloric acid will cause [PtCl6] to be released into the solution. 2-Effective desorption from adsorption is crucial, so controlling the concentration of hydrochloric acid medium during adsorption and desorption is extremely important. Ultimately, the 2 mol / L hydrochloric acid medium concentration in Example 2 was determined to be the optimal adsorption condition.

[0099] Examples 10-14

[0100] Examples 10-14 selected national standard materials No. 2-7 from GSB04-3313-2019 as test samples (sample No. 2 in Example 10, sample No. 3 in Example 11, sample No. 4 in Example 2, sample No. 5 in Example 12, sample No. 6 in Example 13, and sample No. 7 in Example 14). The mass values ​​and uncertainties of the standard materials are shown in Table 1. The above experimental steps were followed to verify the precision and accuracy of the method. Seven independent parallel determinations were performed, and the average value was taken. The determination results are shown in Table 4.

[0101] Table 4 Results of Method Precision and Accuracy Measurements

[0102]

[0103] The calculation results are shown in Table 4. The difference between the measured value and the standard value is less than the uncertainty requirement, and the accuracy of the method meets the requirements.

[0104] Example 15

[0105] Example 15: Two pieces of unknown platinum jewelry from a jewelry manufacturing company were selected and marked as Pt950 and Pt990, respectively, as experimental subjects. The platinum content of these jewelry pieces was determined by following the steps described above.

[0106] Calculations showed that the platinum content was 97.32%, and the method's precision and accuracy met the testing requirements.

[0107] Example 16

[0108] Example 16 uses an unknown platinum alloy sample from a precious metal materials processing company as the experimental object. The platinum content is determined by following the steps described above.

[0109] Calculations showed that the platinum content was 96.18%, and the method's precision and accuracy met the testing requirements.

[0110] In summary, this invention provides an automated potentiometric titration method for determining the platinum content in platinum jewelry, relating to the field of precious metal composition analysis and detection technology. The method mainly includes: dissolving the platinum jewelry sample in aqua regia and using a separating reagent to precipitate and separate interfering precious metal elements such as palladium, gold, and silver. Subsequently, the solution is adjusted to a specific hydrochloric acid concentration and passed through a strongly basic anion exchange resin column, allowing platinum to be selectively adsorbed as chloroplatinate complex anions, thereby completely separating it from base metal ions and obtaining a purified platinum solution. Then, under inert gas protection, an excess of stannous chloride standard solution is added to the purified solution to completely reduce platinum(IV) to platinum(II). Finally, the remaining stannous chloride is automatically potentiometrically titrated using cerium sulfate standard solution, and systematic error correction is performed using a complete blank test. The platinum content is then calculated. This method innovatively integrates interfering element separation, ion exchange purification, back titration, and automated potentiometric detection technologies, and optimizes the electrode system (preferably a combination of a gold electrode and a dual salt bridge reference electrode). The method provided by this invention has the advantages of high accuracy, good precision, strong anti-interference ability, and relatively simple and reliable operation. It is suitable for the accurate determination of platinum content in platinum jewelry and platinum alloys of various purities such as Pt900, Pt950, and Pt990.

[0111] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A method for determining the platinum content in platinum jewelry by automatic potentiometric titration, characterized in that, Includes the following steps: S1. Sample dissolution and preliminary impurity separation: Dissolve the platinum jewelry sample in aqua regia, evaporate and repeatedly add hydrochloric acid to remove nitric acid, and obtain a platinum-containing solution; add a separation reagent to the platinum-containing solution to precipitate and separate at least one of palladium, gold and silver, and obtain a preliminarily purified platinum-containing filtrate. S2, Ion exchange adsorption and elution: The platinum-containing filtrate obtained in step S1 is passed through a strong basic anion exchange resin column, so that platinum is selectively adsorbed in the form of hexachloroplatinate ions. After washing with low-concentration hydrochloric acid to remove the unadsorbed base metal cations, it is eluted with high-concentration hydrochloric acid, and the purified platinum eluent is collected. S3. Back titration: Under inert gas protection, the platinum eluent obtained in step S2 is added to an excess of stannous chloride standard solution to reduce tetravalent platinum to divalent platinum; the remaining stannous chloride after reduction is then subjected to automatic potentiometric titration with cerium sulfate standard solution, and the volume of cerium sulfate standard solution consumed is recorded. V 1 Simultaneously, record the volume of cerium sulfate standard solution consumed in the blank titration. V 0 ; S4. Platinum content calculation: The platinum content is calculated based on the concentration of the cerium sulfate standard solution and the difference between the sample titration volume and the blank titration volume.

2. The method for determining the platinum content in platinum jewelry by automatic potentiometric titration according to claim 1, characterized in that, In step S4, the formula for calculating the platinum content is as follows: ； In the formula: w This refers to the mass fraction of platinum in platinum jewelry; C This represents the concentration of the cerium sulfate standard solution, expressed in mol / L. V 0 This represents the volume of cerium sulfate consumed in the blank test, in mL. V 1 The volume of cerium sulfate consumed in titrating the sample, in mL; M Pt The molar mass of platinum is 195.08, in g / mol. m represents the sample mass, expressed in grams.

3. The method for determining the platinum content in platinum jewelry by automatic potentiometric titration according to claim 1, characterized in that, In step S2, the strongly basic anion exchange resin is a quaternary ammonium-based strongly basic anion exchange resin with a polystyrene-divinylbenzene backbone.

4. The method for determining the platinum content in platinum jewelry by automatic potentiometric titration according to claim 1, characterized in that, In step S3, the automatic potentiometric titration uses a combined gold ring electrode as the indicator electrode and a dual salt bridge reference electrode as the reference electrode.

5. The method for determining the platinum content in platinum jewelry by automatic potentiometric titration according to claim 1, characterized in that, In step S1, the separation reagent includes sulfur dioxide and / or dimethylglyoxime, used to precipitate and separate gold and palladium, respectively.

6. The method for determining the platinum content in platinum jewelry by automatic potentiometric titration according to claim 1, characterized in that, In step S2, the platinum-containing filtrate is adjusted to a specific hydrochloric acid concentration in a hydrochloric acid medium before ion exchange adsorption is performed. The hydrochloric acid medium is a low-concentration hydrochloric acid with a concentration of 1-3 mol / L. The high-concentration hydrochloric acid is a hydrochloric acid solution with a concentration of 4-8 mol / L.

7. The method for determining the platinum content in platinum jewelry by automatic potentiometric titration according to claim 1, characterized in that, In step S3, the inert gas is high-purity nitrogen, which is introduced for 5-10 minutes before pre-reduction, and the hydrochloric acid medium is controlled at 1-3 mol / L; the mass concentration of the stannous chloride solution is 8-12%, and the amount added is based on the solution color changing from pale yellow to a stable reddish-brown, with an excess of 2-5 mL.

8. The method for determining the platinum content in platinum jewelry by automatic potentiometric titration according to claim 1, characterized in that, In step S2, the flow rate of the ion exchange column is 0.5-2 mL / min, the flow rate of the washing exchange column is 1-3 mL / min, and the elution flow rate is 0.5-2 mL / min.

9. The method for determining the platinum content in platinum jewelry by automatic potentiometric titration according to claim 1, characterized in that, Before step S1, there are also resin pretreatment and column packing pretreatment steps.

Images