Titration-based assay for measuring gold in gold-sulfite treatment fluids

Abstract

The subject matter disclosed herein relates to the technology of a titration-based assay method for measuring gold (Au) concentration in a gold treatment fluid. Exemplary methods may include adding a complexing agent and / or a pH adjusting agent to achieve a sharp inflection point in a titration curve.

Description

Technical Field

[0001] The disclosed subject matter relates to chemical measurement methods, and more particularly, to a titration-based assay method for measuring gold in a gold treatment solution. Background Art

[0002] Various methods can be used to assay gold and its concentration in a solution. Some methods have been applied to treatment solutions. Treatment solutions containing gold in the form of soluble sulfite complexes avoid the more dangerous gold cyanide complexes. Gold sulfite baths can provide improved ductility and throwing power, good alloy deposition, and tolerance to impurities.

[0003] Certain assay techniques have been used to assay the gold concentration in a solution, including atomic absorption spectroscopy (AAS), inductively coupled plasma (ICP), and polarography, XRF, and spectroscopy after reaction with selective reagents. Unfortunately, each of these methods may have drawbacks, such as open flames, complex instrumentation, and / or the use of toxic reagents. These methods may also encounter difficulties in automation and may produce inaccurate results. In addition, the use of toxic reagents may make them unsuitable for use in the cleanroom environment of a semiconductor factory.

[0004] Accordingly, there is a need for a simple and reliable method for assaying the gold concentration in a gold-sulfite electroplating solution that can be easily automated and does not require the use of toxic reagents or complex instrumentation. Summary of the Invention

[0005] To address the problems of inaccuracy and toxicity in measurement, the disclosed subject matter provides a simple and reliable assay method for quantitatively measuring the gold (Au) concentration in a gold-sulfite electrodeposition solution.

[0006] The disclosed subject matter provides a titration-based assay method for measuring gold (Au) in a gold-sulfite treatment solution. Exemplary methods include adding a complexing agent having a predetermined concentration to the treatment solution; adding a gold-sulfite solution to the treatment solution; adding a metal salt having a predetermined concentration to the treatment solution; and assaying the gold concentration by measuring the endpoint of a back titration. The complexing agent reacts with Au in a first reaction, and the metal salt reacts with the remaining complexing agent in a second reaction.

[0007] In certain embodiments, the first product of the first reaction has a stability constant greater than that of gold-sulfite.

[0008] In certain embodiments, the second product of the second reaction has a stability constant smaller than that of the first product of the first reaction.

[0009] In certain embodiments, the first reaction produces a first precipitation product, and the second reaction produces a second precipitation product.

[0010] In some embodiments, the treatment liquid is an electroplating solution.

[0011] In some embodiments, the treatment liquid comprises an electroplating metal selected from nickel, cobalt, iron, and combinations thereof.

[0012] In some embodiments, the complexing agent is selected from the group consisting of: thiourea, EDTA, thiosulfate, nitrilotriacetic acid, iminodisuccinic acid, polyaspartic acid, S,S-ethylenediamine-N,N-disuccinic acid, methylglycine diacetic acid, L-glutamic acid, N,N-diacetic acid, salts thereof, and combinations thereof.

[0013] In some embodiments, the method further comprises adding a pH adjusting reagent to the treatment liquid.

[0014] In some embodiments, the method further comprises adding a pH adjusting reagent to the treatment liquid before adding the gold-sulfite solution.

[0015] In some embodiments, the pH adjusting reagent decreases the pH value of the treatment liquid.

[0016] In some embodiments, the pH adjusting reagent is selected from nitric acid, hydrochloric acid, sulfuric acid, and combinations thereof.

[0017] In some embodiments, the metal salt is selected from Ag, Cu, Fe, Al, and combinations thereof.

[0018] In some embodiments, the back titration comprises determining the Au concentration based on the difference between the amount of the end point volume from the blank determination and the amount of the end point of the analyte determination.

[0019] In some embodiments, the method further comprises tracking the titration using a silver-billet electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Reference will now be made in detail to various exemplary embodiments of the disclosed subject matter, which are illustrated in the accompanying drawings. The accompanying drawings are used to further illustrate the various embodiments and to explain all of the principles and advantages in accordance with the disclosed subject matter, wherein like reference numerals refer to like or functionally similar elements throughout the separate views.

[0021] Figure 1 An image showing the expected and measured Au concentrations in one embodiment of the disclosed subject matter is provided.

[0022] FIG. 2A provides the results of titrations performed at different expected concentrations in potential versus titrant volume in one embodiment of the disclosed subject matter. FIG. 2B provides the results of titrations performed at different expected concentrations in slope versus titrant volume in one embodiment of the disclosed subject matter.

[0023] Figure 3 Provide the results of titration data points at the expected concentrations in one embodiment of the disclosed subject matter.

[0024] Figure 4A provides the results of titrations performed with three complexing agents in potential versus titrant volume in one embodiment of the disclosed subject matter. Figure 4B provides the results of titrations performed with three complexing agents in slope versus titrant volume in one embodiment of the disclosed subject matter.

[0025] It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the disclosed subject matter. Detailed Description

[0026] The disclosed subject matter provides methods for using titration to measure the amount of Au in a solution containing an Au analyte. Such methods can be applied to Au solutions for different purposes, such as determining, monitoring, measuring, or assaying the Au concentration in the Au solution.

[0027] For clarity, but not by way of limitation, the embodiments of the disclosed subject matter of the present invention are divided into the following subsections:

[0028] I. Definitions

[0029] II. Methods of Titration

[0030] I. Definitions

[0031] Within the context of the present invention and in the particular context in which each term is used, the terms used in this specification generally have their ordinary meaning in the art. Certain terms are discussed below or elsewhere in this specification to provide additional guidance to the practitioner in describing the compositions and methods of the disclosed subject matter and how to make and use them.

[0032] For the purposes of interpreting this specification, the following definitions will apply and, where appropriate, terms used in the singular will also include the plural and vice versa.

[0033] As used herein, the term "about" or "substantially" means within an acceptable error range of a particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, "about" can mean within 3 or more standard deviations in accordance with practice in the art. Alternatively, "about" can mean a range of up to 20%, up to 10%, up to 5%, and up to 1% of a given value. Or, for example, with respect to biological systems or processes, the term can mean within an order of magnitude of the value, within 5-fold, and within 2-fold.

[0034] As used herein, when used in the context of the concentration of metal ions in a solution, the term "high level" refers to a concentration in the range of grams per liter (g / L).

[0035] As used herein, when used in the context of the concentration of metal ions in a solution, the term "low level" refers to a concentration in the parts per million (ppm) range.

[0036] As used herein, the term "trace" refers to a concentration less than 1000 ppm. In certain embodiments, the trace level refers to a concentration range of 0.1 ppm to 1000 ppm.

[0037] The ranges provided herein should be understood as shorthand for all values within the range. For example, a range of 1 to 50 should be understood to include any number, combination of numbers, or sub-range selected from the group consisting of: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50, as well as all intermediate decimal values between the aforementioned integers, such as 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, and 1.9. Unless otherwise specified, the ranges disclosed herein, such as "from about X to about Y", include about X and about Y and the range limitations of X and Y. With respect to sub-ranges, "nested sub-ranges" that extend from either endpoint of the range are specifically encompassed. For example, the nested sub-ranges of the exemplary range 1 to 50 may include 1 to 10, 1 to 20, 1 to 30, and 1 to 40 in one direction, or 50 to 40, 50 to 30, 50 to 20, and 50 to 10 in the other direction.

[0038] As used herein, the term "predetermined concentration" refers to a known, target, standard, or most preferred concentration of a component in a solution.

[0039] As used herein, the term "selective" or "selectively" refers to a specific monitoring, measurement, or determination of, for example, the characteristics of a particular or specific component. For example, a selective measurement of an ion refers to the measurement of a particular or predetermined target ion from among a plurality of ions present in a solution.

[0040] As used herein, the term "accurate" or "accurately" refers to a measurement or determination that is, for example, relatively close or approaching an existing or true value, standard, or known measurement or value. In certain embodiments, the measurement or determination accuracy error is less than ±5%, has a standard deviation of less than 0.02, and / or a residual standard deviation (RSD) of less than 4%.

[0041] As used herein, the term "about" or "substantially" means within an acceptable error range of a particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measuring system. For example, "about" can mean a range of up to 20%, up to 10%, up to 5%, and / or up to 1% of a given value.

[0042] As used herein, the term "treatment solution" refers to a chemical solution used to determine the concentration of a substance in a solution by reacting the substance with a known amount of a standard solution. Treatment solutions are used in several industries, including electroplating / electroless plating, metallurgy, chemistry, medicine, and other industries that require the measurement, monitoring, and control of analytes.

[0043] As used herein, the term "stability constant" (also known as the formation constant K) refers to a measure of the strength of the interaction between two or more chemical species (e.g., metal ions and ligands). It quantitatively describes the equilibrium constant of the complex formation reaction in solution and refers to the stability of the resulting complex. The larger the stability constant, the more stable the complex and the greater / stronger the tendency of the reactants to form the complex.

[0044] As used herein, the term "complexing agent" refers to a substance that forms a complex with metal ions to control the concentration of metal ions in a solution for purposes such as titration. The use of complexing agents can have several important roles in titration chemistry. For example, but not limited to, the addition of a complexing agent can shift the equilibrium towards the formation of a metal-ligand complex, which can make it easier to measure the concentration of metal ions. Some complexing agents can include (but are not limited to) EDTA, cyanide, dithizone, thiourea, thiosulfate, and NTA.

[0045] As used herein, the term "silver-wire electrode" refers to a type of electrode used in electrochemistry to measure the concentration of certain ions in a solution. It can include a silver rod partially immersed in the solution being measured. When a potential is applied to the silver-wire electrode, silver ions are released into the solution, and the silver ions react with other ions in the solution to produce a current. By measuring the current and / or potential, the concentration of the measured ions can be determined.

[0046] As used herein, the term "back titration" (also known as reverse titration) refers to a titration method used to determine or measure the amount of a substance present in a sample. This method can be used when direct titration is not possible due to the nature of the sample or the reaction being studied.

[0047] As used herein, the term "blank determination" (also known as "blank titration") refers to a control titration process carried out in the absence of the analyte (the substance being determined) in order to correct for any impurities or contaminants in the titrant or the solvent used in the titration. The blank determination can be carried out by using the same amount of solvent and the same amount of titrant as in the actual titration, but without adding any analyte. The endpoint of the blank determination is determined using the same method as in the actual titration (e.g., using an indicator or an instrument such as a potentiometer or pH meter). Subsequently, the volume of titrant used in the blank determination (also known as blank vend) is subtracted from the volume of titrant used in the actual titration to determine the volume of titrant required to neutralize the analyte in the sample and to correct for any impurities or contaminants that may affect the titration. Using a blank determination can be important for ensuring that the titrant and solvent are free of interfering substances that may affect the accuracy of the titration.

[0048] As used herein, the term "analyte determination" (also known as analyte titration) refers to a control titration process carried out in the presence of the analyte (the substance being determined) in order to measure the endpoint of the titrant in a solution containing the analyte, which is used to compare with the endpoint of the titrant in the solution in the blank titration to determine the analyte concentration.

[0049] As used herein, the term "titrant" refers to a standard solution containing a reagent of known concentration that undergoes a chemical reaction with the "reactant" or "unknown species" in the sample solution of unknown concentration to be determined. "Titration" is a determination procedure that involves the repeated standard addition of a known volume of the titrant solution to the assay solution (containing the sample solution), while monitoring the concentration of an indicator species that participates in the reaction between the titrant and the reactant or is indirectly affected by this reaction.

[0050] As used herein, the term "equivalence point" refers to the point at which the reaction between the titrant and the reactant in the titration is complete, corresponding to the stoichiometric balance between the number of moles of the titrant and the number of moles of the reactant in terms of forming a compound or complex.

[0051] As used herein, the term "titration endpoint" refers to a relatively rapid change in the concentration of the indicator species after the equivalence point has been reached, as additional titrant is added to the assay solution. The concentration of the unknown species in the sample solution can be calculated based on the volume of the titrant solution added to the assay solution at the equivalence point (approximately equivalent to the endpoint). "Back titration" involves the standard addition (to the assay solution) of a back titrant reagent that reacts with the unknown species. An excess of the back titrant reagent is added to the assay solution, and then it is allowed to react with the titrant in the titration back to the equivalence point.

[0052] As used herein, the term "titration curve" refers to a plot of the concentration of a titration indicator species in a solution, or a parameter proportional thereto, versus the volume of titrant solution added to the solution being assayed. It may be more convenient to use a concentration parameter proportional to the concentration of the indicator species, especially when the indicator species participates in a complexation reaction involving a competing complexing agent. The endpoint of the titration can be determined by a feature of the curve corresponding to a rapid change in the concentration of the indicator species (e.g., a knee or inflection point of the curve). Detection of the titration endpoint can be facilitated by differentiating the titration curve, which converts the inflection point into a peak. Titration data can be processed as a titration curve or plot, but such data can be tabulated and used directly, for example, by a computer, and the term "titration curve" includes tabular data.

[0053] The methods of the disclosed subject matter can be applied to various types of solutions, including electroplating solutions. In certain embodiments, the treatment solution can include gold-sulfite. Those skilled in the art will appreciate that a wide variety of forms of gold-sulfite or gold and its compounds are applicable herein. In certain embodiments, the treatment solution can include gold-sulfite.

[0054] II. Methods of Titration

[0055] The disclosed subject matter provides techniques for determining and measuring gold in a gold-sulfite treatment solution, such as an electrodeposition solution. In certain aspects, the techniques of the disclosed subject matter can provide a safe and non-toxic method for determining the gold concentration in a treatment solution, including gold-sulfite, that has accurate, rapid, and effective measurement results. In certain embodiments, the methods of the disclosed subject matter can facilitate process control of Au in a metal alloy electroplating bath.

[0056] Such methods use simpler titration methods, where non-toxic reagents or sophisticated assay instruments are used. Additionally, such methods are faster, less costly, and easily automated in a cleanroom environment of a manufacturing industry, such as the semiconductor industry.

[0057] The methods of the disclosed subject matter can be incorporated into existing methods as an extension of the application, including determining, monitoring, and / or assaying the Au(I) concentration in a gold-sulfite electrodeposition solution. Additionally, such methods of the disclosed subject matter can be applied to new chemical monitoring and / or measurement systems to determine the Au(I) concentration in a gold-sulfite electrodeposition solution.

[0058] In an exemplary method, a titration-based assay for measuring gold (Au) in a gold-sulfite treatment solution can be implemented as follows. A complexing agent having a predetermined concentration is added to the treatment solution. A gold-sulfite solution is added to the treatment solution, and then a metal salt having a predetermined concentration is added. The concentration of Au is determined by measuring the endpoint of the back-titration. In such methods, the complexing agent reacts with the complexing agent in a first reaction, and the metal salt reacts with the remaining complexing agent in a second reaction.

[0059] In the first reaction during the titration-based assay for measuring gold-sulfite, after adding the complexing agent, the gold-sulfite compound is destroyed, which can be achieved by forming a new Au complex (Au(I)-X, where X is a ligand of the complexing agent) with a greater stability constant (e.g., its K≥10 23 , more gold-sulfite, K~10 10 ) in the treatment solution. In an alternative embodiment, substantially all of the Au can be precipitated from the treatment solution in the form of a precipitant.

[0060] After all of the Au(I) has been substantially removed from the treatment solution, a second complex can be formed via a second reaction between the excess / remaining complexing agent and the metal salt, which can be achieved by maintaining a second complex (M-X, where M is a metal element and X is a ligand of the complexing agent) with a smaller stability constant (e.g., its 10 10 ≤K≤10 23 ). Thus, the second complex can be precipitated during the second reaction. The endpoint of the titration can be measured at the stopping point of the second reaction between the remaining complexing agent and the metal salt. In combination with the back-titration, the titration volume / concentration of the first reaction can be determined based on the difference between the titration volume / concentration of the back-titration and the titration volume / concentration of the second reaction.

[0061] A complexing agent X having a predetermined concentration can be added to form a new Au complex. As embodied herein, the first reaction can be represented by the following chemical equation:

[0062] [W]Gold-sulfite + [S1]X- ->Au y1 -X x1 (1)

[0063] y1 and x1 are the standard stoichiometric ratios of gold-sulfite and the complexing agent X, respectively; W and S1 are the amounts of the reactants in the first reaction.

[0064] The metal salt (Me + , a metal element) can be added to the treatment solution in the form of a titration having a predetermined concentration to cause at least a portion of the metal salt (Me + ) to react with substantially all of the precipitant (X -) The reaction between... As embodied herein, the second reaction can be represented by the following equation:

[0065] [T2]Me + +[S2]X - ->Me y2 -X x2 (2)

[0066] where y2 and x2 are the standard stoichiometric ratios of the metal salt and the complexing agent X, respectively; T2 and S2 are the amounts of the reactants in the second reaction. It should be noted that T2 can be easily determined via titration at the end point of (2), and thus, S2 can be calculated via the stoichiometric ratio.

[0067] The same metal salt (Me + ) as the titrant can be used to measure the end point of the back titration. In the blank determination, the reaction can be represented by the following equation:

[0068] [T]Me + +[S]X - ->Me y2 -X x2 (3)

[0069] where T and S are the amounts of the reactants in the blank determination of the analyte-free solution. It should be noted that T can be easily determined via titration at the end point of (3), and S is a predetermined value.

[0070] The titration volume related to the end point in (2) can be subtracted from the back titration volume related to the end point in (3). To obtain the difference, the volume of the complexing agent reacting with gold in (1) can be calculated, and thus, the concentration of Au(I) in the gold-sulfite treatment solution can be determined based on the stoichiometric ratio between the reactants in the equation.

[0071] As embodied herein, the Au concentration can be calculated as follows:

[0072] S = T * y2 / x2 (4)

[0073] S2 = T2 * y2 / x2 (5)

[0074] S1 = S - S2 (6)

[0075] W = S1 * x1 / y1 (7)

[0076] Concentration A u = W / V (8)

[0077] Note: V is the predetermined volume of the analyte solution added to the treatment solution.

[0078] In certain embodiments, the back-titration may include a blank determination and an analyte determination. In certain embodiments, the analyte titration may include adding gold-sulfite as the analyte solution to the treatment solution. The back-titration may determine the Au concentration based on the difference between the amount of the end point from the blank titration and the amount of the end point of the analyte titration. In certain embodiments, the method includes tracking the titration by using a silver-sliver electrode.

[0079] In certain embodiments, the gold-sulfite may react with a complexing agent, and the metal salt may react with the remaining complexing agent. The complexing agent in the treatment solution generally serves as a metal chelator to bind metal ions, typically the ions to be determined or measured. In certain embodiments, the first reaction between the gold-sulfite and the complexing agent and the second reaction between the metal salt and the remaining complexing agent may produce a precipitate for determining the titration end point.

[0080] To achieve the above titration with the desired results, it may be necessary to select a complexing agent and a metal salt to cause precipitation in the solution. Generally, in a solution, the larger the stability constant K of a compound, the greater the tendency to form the compound (e.g., precipitate out in the solution). Therefore, the disclosed subject matter provides a complexing agent that is capable of forming a product (Au-X) having a K greater than that of gold-sulfite in the first reaction. In addition, a product (Me-X) having a K greater than that of gold-sulfite but less than that of Au-X is formed in the second reaction. This enables a titration-based determination method for gold in a gold-sulfite treatment solution.

[0081] In certain embodiments, the complexing agent may be one or more of the following: thiourea, EDTA, thiosulfate, nitrilotriacetic acid, iminodisuccinic acid, polyaspartic acid, S,S-ethylenediamine-N,N'-disuccinic acid, methylglycine diacetic acid, L-glutamic acid, N,N-diacetic acid, their salts, and their combinations. Those of ordinary skill in the art will readily understand that the complexing agent may include standard derivatives of the above selections, such as chelators, chelating agents, or complexing agents.

[0082] In certain embodiments, the treatment solution is an electrodeposition solution. In certain embodiments, the treatment solution includes an electroplating metal selected from nickel, cobalt, iron, aluminum, and combinations thereof.

[0083] In certain embodiments, the method further includes adding a pH adjustment reagent to the treatment solution. The gold-sulfite complex is stable at alkaline pH (K, ~10 10) It is usually stable in solution. When the pH is lowered, the complex can be effectively destroyed, and Au(I) can be converted to Au(III) and / or metallic Au. Such methods can destroy this complex in an acidic pH solution and form a new Au complex (K,≥10 23 ) by adding a pH adjusting reagent. This pH adjusting reagent can produce an effective sharp inflection point for accurate quantification during titration.

[0084] In certain embodiments, the addition of the pH adjusting reagent to the treatment solution can be selective, for example, before or after adding the gold-sulfite solution, because pH adjustment generally does not affect the formation of Au(I)-X or the reaction between gold and the complexing agent. In certain embodiments, the pH adjusting reagent lowers the pH value of the treatment solution.

[0085] In certain embodiments, the pH adjusting reagent is selected from nitric acid, hydrochloric acid, hydrochloric acid, and combinations thereof.

[0086] In certain embodiments, the metal salt is selected from Ag, Cu, iron, Al, and combinations thereof.

[0087] In certain embodiments, the treatment solution is an electroplating solution. In certain embodiments, the method may include adding a pH regulator to the treatment solution.

[0088] In certain embodiments, the pH regulator lowers the pH value of the treatment solution.

[0089] Additionally, the methods provided by the disclosed subject matter can be used in some scalable applications, including (but not limited to) determining, controlling, and regulating the gold concentration in a gold-sulfite treatment solution.

[0090] Meanwhile, those skilled in the art should understand that, subject to meeting the above stability constant criteria, the methods of the disclosed subject matter can be applied to similar or equivalent analyte solutions, including (but not limited to) gold-sulfide, gold-sulfate, and gold-thiosulfate.

[0091] Examples

[0092] The disclosed subject matter will be better understood by reference to the following examples. The following examples merely illustrate the disclosed subject matter of the invention and should not be construed as limiting the scope of the subject matter in any way. The examples use the following reagents and detectors.

[0093] Reagents: nitric acid, thiourea, EDTA, thiosulfate, silver nitrate, and gold-sulfite electroplating solution.

[0094] Detectors: ECI Qualilab EZ (for feasibility studies), CI Qualifill Libra (for final R & D), and silver-blank electrode.

[0095] For the following examples, these relevant measurement terms regarding the accuracy of the evaluation method can be understood and characterized as follows.

[0096] Accuracy (%) = [((Measured average value) - (Expected value)) / (Expected value)] × 100 (9)

[0097] Relative standard deviation, RSD (%) = (Standard deviation × 100) / (Measured average value) (10)

[0098] Example 1: Au Concentration Measurement

[0099] The method of the disclosed subject matter provides for the measurement of the gold concentration in a gold - sulfite electrodeposition solution in the presence of a pH regulator. The Au concentration (M, g / l, expected target concentration 0.50, low concentration 0.25, high concentration 1.00) in such a solution can be determined as follows.

[0100] Process I blank determination:

[0101] 1) Add deionized water to the reaction vessel (about 50 to 100 ml).

[0102] 2) Add Reagent 1 (complexing agent, thiourea) to the reaction vessel (about 2 to 5 ml depending on the analyte concentration).

[0103] 3) Titrate the resulting mixture with a metal salt (silver nitrate).

[0104] 3) Add Reagent 2 (nitric acid) to the reaction vessel (about 5 to 10 ml depending on the analyte concentration).

[0105] 4) Titrate the resulting mixture with a metal salt.

[0106] 5) Automatically detect the end point via potentiometric titration, selectively by a "fixed potential" setting or an "inflection point" algorithm.

[0107] 6) Record the blank discharge related to the volume at the end point.

[0108] 7) Automatically stop the titration based on a "stopping point" algorithm.

[0109] 8) Clean the reaction vessel and the electrode with a cleaning solution (nitric acid) and deionized water.

[0110] Process II: Analyte determination:

[0111] 1) Add deionized water to the reaction vessel (about 50 to 100 ml).

[0112] 2) Add Reagent 1 (thiourea) to the reaction vessel (about 2 to 5 ml depending on the analyte concentration).

[0113] 3) Add Reagent 2 (nitric acid) to the reaction vessel (about 5 to 10 ml depending on the analyte concentration).

[0114] 4) Add the analyte solution (gold - sulfite) to the reaction vessel (about 2 to 6 ml depending on the analyte concentration).

[0115] 5) Titrate the resulting mixture with the metal salt silver nitrate.

[0116] 6) Automatically detect the end point by the "fixed potential" setting or the "inflection point" algorithm, and record the titration volume in the second reaction.

[0117] 7) Calculate the analyte discharge by subtracting the end - point volume from the blank discharge.

[0118] 8) Automatically calculate the analyte concentration based on the discharge, sample volume, and titrant concentration.

[0119] 9) Automatically stop the titration based on the "stop point" algorithm.

[0120] 10) Clean the reaction vessel and the electrode with the cleaning solution (nitric acid) and deionized water.

[0121] Table 1 summarizes the measurement results of Au concentration based on the online prototype identification data (ECIQualifill Libra). The calculated results of Au concentration illustrate the accuracy and precision of the method in the disclosed examples of the present invention.

[0122] Table 1

[0123]

[0124] Combined with Table 1, Figure 1 generally demonstrates the accuracy and precision of the exemplary method in the examples. As Figure 1 shown, the measurement method is generally linear, indicating that the measured values in the examples increase proportionally with the change in the expected value of the Au concentration in the solution.

[0125] Table 2 shows the potential curve and slope curve for titration (AgNO3 as the titrant) in the examples.

[0126] Table 2

[0127]

[0128] Combined with Table 2, Figures 2A to 2B show the potential curves and slope curves used for titration in this article. The end point of the back titration is the obvious sharp inflection point in the curve. It is worth noting that in the slope curve of Figure 2B, the inflection point and peak point of the Au concentration in the solution illustrate the accuracy and precision. According to the amounts of the analyte and the complexing agent in the first reaction, the Au concentration in the gold-sulfite solution is calculated via the stoichiometric ratio in the first reaction. By measuring the amount of the titrant in the second reaction (related to the end point determined for the analyte) and the amount of the titrant in the blank determination, the amount of the complexing agent in the first reaction is pre-calculated. The calculation can refer to the above equation.

[0129] As shown in Figures 2A to 2B, the end point of the second reaction is determined by a fixed potential setting or an inflection point algorithm, related to a fixed point or inflection point in the curve. After determining the end point, the measured value of the Au concentration is calculated via the above equation based on predetermined parameters and standard parameters.

[0130] Example 2: Long-Term Verification of Au Concentration Measurement

[0131] In this article, a gold-sulfite solution with an expected Au concentration of 0.50 g / l is used in the measurement method to conduct the measurement. Following the same procedures and parameters as the above examples, 92 data points have been measured to test the accuracy and precision of the measurement in the method disclosed by the present invention.

[0132] Table 3 lists the data points regarding the Au concentration in the examples.

[0133] Table 3

[0134]

[0135] Figure 3 Shows the distribution of the data points regarding the Au concentration. All the data points of the examples are distributed within a relatively narrow range, approximately from 0.499 to 0.550, with an accuracy of 4.35%, a standard deviation of 0.01, and an RSD of 2.15%.

[0136] Example 3: Comparison of Different Complexing Agents

[0137] In the examples in this article, different complexing agents are used in the method for the Au concentration in the solution. As described above, a complexing agent with a larger stability constant K is extremely likely to produce a stable product, such as a precipitate, via complexing with the Au ions in the solution. In other words, an ideal complexing agent can produce a complex (Au-X) with a stability constant K substantially greater than that of gold-sulfite (K, 10 10 )

[0138] Meanwhile, the metal complex (Me-X) generated in the second reaction (analyte titration) ideally has a K greater than that of gold-sulfite. Table 4 lists the K values of different complexes Au-X and Ag-X combined with three different complexing agents in solution. It is worth noting that although cyanide can act as a complexing agent to complex gold in a gold-sulfite solution, cyanide causes significant toxicity problems during the process. Additionally, based on the K values in Table 4, cyanide does not effectively complex Ag in the second reaction.

[0139] Table 4

[0140]

[0141] In this article, measurements using different complexing agents (thiourea, thiosulfate, and EDTA) were carried out using the same procedures and parameters as in the above examples. Table 5 lists the measurement results of data points on the titrant volume, potential, and slope for three different complexing agents used in the Au concentration determination method.

[0142] Table 5

[0143]

[0144]

[0145] Combined with the data values in Table 5, Figures 4A to 4B show the potential curves and slope curves in the titration. In these titration curves, the titration volume (AgNO3 as the titrant) is on the horizontal axis. When EDTA is used as the complexing agent, the potential curve becomes a gradually flat line, and the equivalence point is generally not visible. Therefore, EDTA is not an effective complexing agent for measuring the Au concentration.

[0146] Compared with EDTA, thiourea or thiosulfate is more suitable as a complexing agent. As shown in Figures 4A to 4B, the equivalence point of the titration curve is well identified, indicating a sharp inflection point in the slope curve, as shown in Figure 4B. It is worth noting that when thiourea is used as the complexing agent to measure the Au concentration, as shown in Figure 4B, the slope curve is steep and almost vertical around the equivalence point.

[0147] This is because the stability constant K of the product (Au-thiourea) in solution is as high as 10 28 , and the K in the solution changes rapidly. Near the equivalence point, the solution suddenly changes from a weaker compound to a stronger compound (Au-thiourea, with a larger stability constant K).

[0148] In view of the teachings herein, various modifications and changes to the described embodiments will be apparent to those skilled in the art. Accordingly, the disclosure herein is intended to illustrate but not limit the scope of the disclosed subject matter. Further, the principles of the disclosed subject matter may be implemented in various configurations and are not intended to be limited in any way to the specific embodiments presented herein.

[0149] In addition to the various embodiments depicted and claimed, the disclosed subject matter also relates to other embodiments having other combinations of the features disclosed and claimed herein. Thus, the specific features presented herein may be combined with each other in other ways within the scope of the disclosed subject matter such that the disclosed subject matter includes any suitable combination of the features disclosed herein. For purposes of illustration and description, the foregoing description of specific embodiments of the disclosed subject matter has been presented. It is not intended to be exhaustive or to limit the disclosed subject matter to those embodiments disclosed.

[0150] Various patents and patent applications are cited herein, the contents of which are incorporated herein by reference in their entirety.

Claims

1. A titration-based determination method for measuring gold (Au) in a gold-sulfite treatment solution, comprising: a. adding a complexing agent with a predetermined concentration to the treatment solution; b. adding a gold-sulfite solution to the treatment solution; c. adding a metal salt with a predetermined concentration to the treatment solution; d. determining the concentration of Au by measuring the endpoint of the back-titration, wherein the complexing agent reacts with the complexing agent in a first reaction, and the metal salt reacts with the remaining complexing agent in a second reaction.

2. The method according to claim 1, wherein the first product of the first reaction has a larger stability constant than gold-sulfite.

3. The method according to claim 1, wherein the second product of the second reaction has a smaller stability constant than the first product of the first reaction.

4. The method according to claim 1, wherein the first reaction produces a first precipitation product, and the second reaction produces a second precipitation product.

5. The method according to claim 1, wherein the treatment solution is an electroplating solution.

6. The method according to claim 1, wherein the treatment solution contains an electroplating metal selected from the group consisting of nickel, cobalt, iron, and combinations thereof.

7. The method according to claim 1, wherein the complexing agent is selected from the group consisting of: thiourea, EDTA, thiosulfate, nitrilotriacetic acid, iminodisuccinic acid, polyaspartic acid, S,S-ethylenediamine-N,N-disuccinic acid, methylglycine diacetic acid, L-glutamic acid, N,N-diacetic acid, salts thereof, and combinations thereof.

8. The method according to claim 1, further comprising adding a pH adjustment reagent to the treatment solution.

9. The method according to claim 1, further comprising adding a pH adjustment reagent to the treatment solution before adding the gold-sulfite solution.

10. The method according to claim 8, wherein the pH adjustment reagent reduces the pH value of the treatment solution.

11. The method according to claim 8, wherein the pH adjustment reagent is selected from the group consisting of: nitric acid, hydrochloric acid, sulfuric acid, and combinations thereof.

12. The method according to claim 1, wherein the metal salt is selected from the group consisting of: Ag, Cu, Fe, Al, and combinations thereof.

13. The method according to claim 1, wherein the back-titration comprises determining the Au concentration based on the difference between the amount of the endpoint volume from a blank determination and the amount of the endpoint of the analyte determination.

14. The method according to claim 1, further comprising tracking the titration using a silver-sliver electrode.

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