CN111579713A

CN111579713A - Method for testing content of silver in full valence state

Info

Publication number: CN111579713A
Application number: CN202010534100.8A
Authority: CN
Inventors: 吴永鑫; 钟元杰; 康朝晖; 胡必忠; 林文端; 叶佳; 李敬茹
Original assignee: Jinda Nano Tech Xiamen Co ltd
Current assignee: Jinda Nano Tech Xiamen Co ltd
Priority date: 2020-06-12
Filing date: 2020-06-12
Publication date: 2020-08-25

Abstract

The invention relates to a method for testing the content of silver in a full valence state, which comprises the following steps of (1): preparing a potassium thiocyanate standard solution, a silver standard solution and an ammonium ferric sulfate indicator; step (2): calibrating the titer f of the potassium thiocyanate standard solution; and (3): converting the silver solution to be detected, and adopting excessive strong reducing agent until all silver ions in the silver solution to be detected become 0 valence, thereby obtaining filter residue; oxidizing the filter residue to obtain a converted silver measuring solution; and (4): and titrating the obtained converted silver solution to be detected by adopting a Flohard method. In the method for testing the content of the silver in the full valence state, the titration degree f and the conversion of the silver solution to be tested are established, expensive analysis equipment is not needed, and the Ag content in the silver solution can be simultaneously measured⁰、Ag⁺、Ag²⁺、Ag³⁺The silver total mass concentration is high, the test accuracy is high, the enterprise standards established by small and medium-sized enterprises can be met, and the popularization of the silver antibacterial agent is facilitated.

Description

Method for testing content of silver in full valence state

Technical Field

The invention relates to a silver analysis and test technology, in particular to a full-valence silver content test method.

Background

The antibacterial property of silver has long been recognized and is widely used in many fields, such as medicine, plastics, bathroom and other industries. The silver species are divided into zero-valent silver and ionic silver according to valence states. Silver ions are positively charged cations of silver atoms with loss of one or more electrons, e.g. Ag⁺、Ag²⁺、Ag³⁺And the like. Usually in the form of an aqueous solution, silver ions have an oxidizing action and are commonly used in daily life for sterilization, disinfection and the like. The silver ions in different valence states have different properties: ag²⁺Is a borderline acid, comparable to Ag⁺Susceptible to hydrolysis to form the hydroxide Ag (OH)₂Thus containing Ag²⁺The solution of (A) is weakly acidic but its hydroxide solubility is large (solubility is equivalent to that of soda), so that Ag (OH) is not generated when a strong base is added₂And (4) precipitating. This may facilitate the discrimination between the silver ions in the monovalent and divalent states.

Silver ions themselves have the disadvantage of changing colour with light, and transparent colourless solutions can turn brown to black. Especially at high temperatures, discoloration is faster under high light. In order to prevent the occurrence of color change, some enterprises adopt nano silver which is not easy to change color to replace ionic silver. However, a disadvantage of nano silver is that the rate of sterilization is not as high as that of ionic silver, that is, the nano silver content is higher than that of ionic silver in order to achieve the same rate of sterilization, which increases the cost and causes difficulty in the manufacturing process.

Therefore, in order to prevent silver discoloration, other enterprises adopt different complexing agents to complex silver ions, such as the thiourea method, the thiocyanate method, the thiosulfate method, the polysulfide method, the halide method and other solvent methods, to prepare colorless silver ion solutions containing different complexing anions. The concentration of silver ions is measured by two methods: (1) instrumental analysis method: can be measured by X-ray fluorescence spectroscopy or atomic absorption spectroscopy. (2) The chemical test method adopts Verahard method to directly titrate silver nitrate solution, and the method is a back opening made of ferric ammonium sulfateNH₄Fe(SO₄)₂0.0500mol/L potassium thiocyanate (KSCN) standard solution is used as a titrant. When the KSCN standard solution was dropped, AgSCN white precipitate was first generated. After quantitative precipitation of Ag + ions, an excess of one drop of the KSCN standard solution was mixed with Fe in the indicator³⁺Ion combination to generate red complex ion [ FeSCN]²⁺When the end point of the titration is reached.

In the actual production test process, experimenters find that the numerical value measured by the Flohard method of certain silver solutions on the market, such as the colorless transparent nano silver solution JDTKS-001 of Jinda nano technology (Xiamen) limited company, is obviously lower than the numerical value content measured by ICP; this phenomenon also causes a comparison between the measurement result of the silver content of "Yinlejie" product of Xiancangwang antibacterial science and technology Co., Ltd and the measurement result of ICP. The reason for this is probably that Ag is added to a specific silver ion solution in the presence of potassium thiocyanate by the Flohard method²⁺、Ag³⁺The precipitation phenomenon cannot be generated. It is not possible to directly and accurately titrate the concentration of all silver ion solutions using the verhath method. Therefore, it is highly desirable to develop a chemical method that can titrate the total concentration of silver ions in a solution containing different valence states.

Disclosure of Invention

The invention aims to solve the problem of the existing chemical test method for the mass concentration of silver solution without universality because different silver solutions contain silver ions with different valence states, and provides a full-valence silver content test method which can simultaneously determine the mass concentration of the silver ions with different valence states, and the method can simultaneously determine that the solution to be tested contains Ag⁰、Ag⁺、Ag²⁺、Ag³⁺The total mass concentration of silver does not need a noble chemical analysis instrument, and meets the requirement of medium and small enterprises for establishing own enterprise standards.

One of the key points of the method is to calibrate the titer f of the potassium thiocyanate standard solution and establish a calculation mode of the titer f, and the titer f can quickly and timely estimate the concentration of the measured silver ions, thereby being beneficial to the estimation of the unknown silver titration amount and further providing reference on grasping the overranging amount of the strong reducing agent.

Preferably, the potassium thiocyanate standard solution is an aqueous solution of potassium thiocyanate, the concentration of the aqueous solution is 0.01-0.1mol/L, preferably 0.03-0.07mol/L, the reaction speed of the aqueous solution with silver is moderate under the concentration condition, the titration end point is convenient to control, and the detection accuracy is improved.

Preferably, the silver standard solution is obtained by adopting 99.99% pure silver powder, adding concentrated nitric acid for heating until silver is dissolved, cooling, and adding deionized water, and preferably, the concentration of Ag & lt + & gt in the silver standard solution is 0.1-2 g/L. The silver standard solution is obtained by reacting the silver powder with higher purity with concentrated nitric acid, thereby ensuring the accurate concentration of the silver standard solution.

Preferably, the mass concentration of the ammonium ferric sulfate in the ammonium ferric sulfate indicator is 50-100g/L, preferably 60-90g/L, more preferably 70-80g/L, and a suitable ammonium ferric sulfate indicator influences the color development sensitivity.

The other key point of the invention is the conversion of the silver measuring solution, and the principle of the invention is that under the acidic condition, the silver solution containing different valence states is pretreated by excessive strong reducing agent to form silver slag precipitate, then the silver slag is oxidized to obtain monovalent silver solution, and then the monovalent silver solution is titrated by potassium thiocyanate to determine the mass fraction of the silver solution. The difficulty in achieving this is that the valence state of the silver in solution may not be uniform and cannot be measured in a consistent titration process. According to the method, excessive strong reducing agent, preferably at least one of borohydride, hydrazine hydrate or sulfide, is adopted to precipitate the silver in the silver solution to be detected, and preferably, the molar ratio of the estimated silver content in the silver solution to be detected to the using amount of the strong reducing agent is 1:10-1:20, so that complete silver precipitation is ensured, and black or brown or white filter residue is obtained. The filter residues with different colors can appear because the silver residues obtained by reducing the silver solution by different reducing agents have different particle sizes and finally show different colors.

Preferably, the pH is adjusted at the time of precipitation in step (3) to 1 to 6.5, preferably 2 to 4, more preferably 2.5 to 3, and the precipitation of silver is accelerated and completed under acidic conditions.

In order to oxidize all the silver in the filter residue into Ag +, excessive concentrated nitric acid is poured into a polytetrafluoroethylene container, the obtained filter residue is placed, the filter residue is heated and kept boiling on an electric hot plate, then the wall of the cup is washed by water, and the filter residue is cooled, wherein the key points of the operation comprise: molar equivalent of concentrated nitric acid in polytetrafluoroethylene container: the molar equivalent of the filter residue is 2:1-6:1, so as to ensure that the filter residue is fully reacted; the electric heating plate is set at 90-100 deg.C for 10-60min, and then kept boiling for 5-10min, and the filter residue is subjected to nitrolysis by heating

Ag+2HNO₃(concentrated) ═ AgNO₃+NO₂+H₂O

3Ag+4HNO₃(rare) ═ 3AgNO₃+NO+2H₂O

Silver in the filter residue is changed from 0 valence to 1 valence through nitrohydrolysis, and the silver is completely put into the solution, so that the content can be directly and accurately measured by using a Verahard method.

The specific scheme is as follows:

a full valence state silver content testing method comprises the following steps:

step (1): preparing a potassium thiocyanate standard solution, a silver standard solution and an ammonium ferric sulfate indicator;

step (2): calibrating the titer f of a potassium thiocyanate standard solution

Absorbing the silver standard solution with the concentration of C₁Volume is V₁Adding concentrated nitric acid and the ferric ammonium sulfate indicator solution, titrating with a potassium thiocyanate solution to be calibrated to be light red and stable, reading the volume number A of the consumed potassium thiocyanate, and then: titer f ═ C of standard potassium thiocyanate solution₁×V₁/A；

And (3): conversion of silver solution to be tested

Taking a silver solution to be detected, adding an acidic solution with the volume of m, adjusting the pH value to be less than 7, adding an excessive strong reducing agent into the solution until all silver ions become 0, standing, and removing supernatant to obtain filter residue; pouring excessive concentrated nitric acid into a polytetrafluoroethylene container, then putting the obtained filter residue, heating and keeping boiling on an electric hot plate, then washing the cup wall with water, and cooling to obtain a converted silver measuring solution;

and (4): adopting a Flohard method to titrate the obtained converted silver measuring solution, taking the potassium thiocyanate standard solution in the step (1) as a titrant, taking the ferric ammonium sulfate indicator in the step (1), and recording the volume V of the consumed potassium thiocyanate standard solution₂Then, the titer f × of the full valence state silver content ═ potassium thiocyanate standard solution of the silver solution to be detected and the volume V of the potassium thiocyanate standard solution₂Volume m of silver solution to be measured.

Further, Ag exists in the silver solution to be detected⁰、Ag⁺、Ag²⁺Or Ag³⁺At least one of;

optionally, the standard solution of potassium thiocyanate in the step (1) is an aqueous solution of potassium thiocyanate, and the concentration is 0.01-0.1mol/L, preferably 0.03-0.07 mol/L.

Further, the silver standard solution in the step (1) is obtained by adding concentrated nitric acid into 99.99 wt% of pure silver powder, heating until silver is dissolved, cooling, and adding deionized water, preferably, the concentration of Ag + in the silver standard solution is 0.1-2 g/L.

Further, in the step (1), the ammonium ferric sulfate indicator is prepared by adding ammonium ferric sulfate into deionized water for dissolving, and then adjusting to a light red color with concentrated nitric acid for disappearance, and preferably, the mass concentration of the ammonium ferric sulfate in the ammonium ferric sulfate indicator is 50-100 g/L.

Further, in the step (3), the acidic solution is an inorganic acid, preferably at least one of nitric acid, sulfuric acid or hydrochloric acid.

Further, in step (3), the pH is adjusted to 1-6.5.

Further, in the step (3), the strong reducing agent is at least one of borohydride, hydrazine hydrate or sulfide.

Further, the molar ratio of the estimated silver content in the silver solution to be detected in the step (3) to the amount of the strong reducing agent is 1:10-1: 20.

Further, in the step (3), the filter residue is at least one of black filter residue, brown filter residue and white filter residue.

Further, in the step (3), the molar equivalent of the concentrated nitric acid in the polytetrafluoroethylene container is as follows: the molar equivalent of the filter residue is 2:1-6: 1;

optionally, in the step (3), the heating temperature on the electric hot plate is 90-100 ℃, the heating time is 10-60min, the micro boiling is kept for 5-10min, the solution is subjected to nitrolysis, then the wall of the cup is washed with water, and the converted solution for measuring silver is obtained after cooling.

Has the advantages that:

in the method for testing the content of the silver in the full valence state, the titration degree f and the conversion of the silver solution to be tested are established, expensive analysis equipment is not needed, and the content of the Ag can be simultaneously measured⁰、Ag⁺、Ag²⁺、Ag³⁺The silver total mass concentration is high, the test accuracy is high, the enterprise standards established by small and medium-sized enterprises can be met, and the popularization of the silver antibacterial agent is facilitated.

Detailed Description

Preferred embodiments of the present invention will be described in more detail below. While the following describes preferred embodiments of the present invention, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein. The examples do not specify particular techniques or conditions, and are performed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available. In the following examples, "%" means weight percent, unless otherwise specified.

Example 1

A method for testing the content of silver in a full valence state comprises the following steps:

4.8500g of potassium thiocyanate was weighed out in a 100mL beaker, dissolved in water, transferred to a 1000mL volumetric flask, and added to the scale when the concentration of potassium thiocyanate in c (KSCN) ═ 0.05mol/L was reached.

Silver standard solution: weighing 1.0000g of 99.99% pure silver powder, placing the silver powder in a 200mL beaker, adding 2.56mL of 50mL of 68% concentrated nitric acid, heating the beaker in a surface dish and a water bath until the silver is dissolved, cooling, transferring the silver powder into a 1000mL volumetric flask, diluting the silver powder with deionized water until the scales are scaled, and shaking up.

Ammonium ferric sulfate { NH₄Fe(SO₄)₂Indicator: 80.0g of ammonium ferric sulfate is weighed, placed in a 1000mL beaker, dissolved by adding a proper amount of deionized water, adjusted to be light red by 60% concentrated nitric acid, disappeared and diluted to 1000 mL.

Step (2): calibrating the titer f of a potassium thiocyanate standard solution

Sucking 10mL of silver standard solution, placing the silver standard solution into a 250mL conical flask, adding water to dilute the silver standard solution to 100mL, adding 5mL of concentrated nitric acid, adding 1-2 mL of 80g/L ferric ammonium sulfate indicator solution, titrating the solution to be calibrated to be light red and stable by using a potassium thiocyanate solution to be calibrated, reading the milliliter number A, and reading the titer f which is 10mL multiplied by 1000 mu g/A (mu g/mL)

And (3): conversion of silver solution to be tested

Taking a silver solution sample to be detected, adding 1M nitric acid solution into the sample with the volume of 10mL, adjusting the total pH value of the solution to be 3.0, then adding 0.5g of sodium borohydride into the solution to change all silver ions into 0, standing the solution, and removing supernatant to obtain the required black or brown or white filter residue.

Pouring excessive concentrated nitric acid into a polytetrafluoroethylene container, so that the molar equivalent of the concentrated nitric acid added is as follows: the molar equivalent of the filter residue is 3: 1. Then putting into filter residue, heating on electric hot plate for 30min at 100 deg.C for 30min, keeping boiling for 10min, performing nitrohydrolysis, washing the cup wall with appropriate amount of water, and cooling. Wherein all silver is converted to monovalent silver ions, present as Ag +.

And (4): titrating the monovalent silver ions in the converted silver measuring solution obtained by the Verahard method with 0.1mL of ammonium ferric sulfate { NH ]₄Fe(SO₄)₂And 0.05mol/L of potassium thiocyanate standard solution is used as a titrant. When the potassium thiocyanate standard solution was added dropwise, a white precipitate of AgSCN was first produced. One drop of sulfur in excess after quantitative precipitation of Ag + ionsFe in standard solution of potassium cyanate and indicator³⁺Ion combination to generate red complex ion [ FeSCN]²⁺When the end point of the titration is reached. The mL of potassium thiocyanate standard solution consumed was recorded at 30 mL.

The silver content (mu g/mL) of the sample to be tested is equal to the titer f of the potassium thiocyanate standard solution, multiplied by the volume of the potassium thiocyanate standard solution, of 30mL divided by the volume of the silver solution to be tested, of 10 mL.

The final measured concentration of silver ions of sample 1 was 5100 ppm.

Example 2

Step (2): calibrating the titer f of a potassium thiocyanate standard solution

And (3): conversion of silver solution to be tested

Taking a silver solution sample to be detected 2, adding a 1M nitric acid solution into the sample with the volume of 20mL, adjusting the total pH value of the solution to be 2.0, then adding 1.5g of sodium borohydride into the solution to change all silver ions into 0, standing the solution, and removing supernatant to obtain the required black or brown or white filter residue.

Pouring excessive concentrated nitric acid into a polytetrafluoroethylene container, so that the molar equivalent of the concentrated nitric acid added is as follows: the molar equivalent of the filter residue is 4: 1. Then putting into filter residue, heating on electric hot plate for 30min at 100 deg.C for 30min, keeping boiling for 10min, performing nitrohydrolysis, washing the cup wall with appropriate amount of water, and cooling. Wherein all silver is converted to monovalent silver ions, present as Ag +.

And (4): titrating the monovalent silver ions in the converted silver measuring solution obtained by the Verahard method with 0.1mL of ammonium ferric sulfate { NH ]₄Fe(SO₄)₂And 0.05mol/L of potassium thiocyanate standard solution is used as a titrant. When the potassium thiocyanate standard solution was added dropwise, a white precipitate of AgSCN was first produced. After the Ag + ions are quantitatively precipitated, one drop of excess potassium thiocyanate standard solution and Fe in the indicator³⁺Ion combination to generate red complex ion [ FeSCN]²⁺When the end point of the titration is reached. The mL of consumed potassium thiocyanate standard solution was recorded at 50 mL.

The silver content (mu g/mL) of the sample to be tested is equal to the titer f of the potassium thiocyanate standard solution, multiplied by the volume of the potassium thiocyanate standard solution of 50mL divided by the volume of the silver solution to be tested of 20 mL.

The final measured concentration of silver ions for sample 2 was 4700 ppm.

Example 3

Ammonium ferric sulfate { NH₄Fe(SO₄)₂Indicator: 80.0g of ammonium ferric sulfate is weighed, placed in a 1000mL beaker, dissolved by adding a proper amount of deionized water, adjusted to be light red by 60 wt% of concentrated nitric acid, disappeared and diluted to 1000 mL.

Step (2): calibrating the titer f of a potassium thiocyanate standard solution

And (3): conversion of silver solution to be tested

Taking a silver solution sample to be detected, adding 1M nitric acid solution into the silver solution sample with the volume of 15mL, adjusting the total pH value of the solution to be 4.0, then adding 0.5g of sodium borohydride into the solution to change all silver ions into 0, standing the solution, and removing supernatant to obtain the required black or brown or white filter residue.

Pouring excessive concentrated nitric acid into a polytetrafluoroethylene container, so that the molar equivalent of the concentrated nitric acid added is as follows: the molar equivalent of the filter residue is 5: 1. Then putting into filter residue, heating on electric hot plate for 30min at 100 deg.C for 30min, keeping boiling for 10min, performing nitrohydrolysis, washing the cup wall with appropriate amount of water, and cooling. Wherein all silver is converted to monovalent silver ions, present as Ag +.

And (4): titrating the monovalent silver ions in the converted silver measuring solution obtained by the Verahard method with 0.1mL of ammonium ferric sulfate { NH ]₄Fe(SO₄)₂And 0.05mol/L of potassium thiocyanate standard solution is used as a titrant. When the potassium thiocyanate standard solution was added dropwise, a white precipitate of AgSCN was first produced. After the Ag + ions are quantitatively precipitated, one drop of excess potassium thiocyanate standard solution and Fe in the indicator³⁺Ion combination to generate red complex ion [ FeSCN]²⁺When the end point of the titration is reached. Recording consumed standard solution of potassium thiocyanateThe volume of the solution is 30 mL.

The silver content (mu g/mL) of the sample to be tested is equal to the titer f of the potassium thiocyanate standard solution, multiplied by the volume of the potassium thiocyanate standard solution, which is 30 mL/15 mL.

The final measured silver ion concentration of sample 3 was 6200 ppm.

Comparative example 1: and (3) determining the silver content of the sample to be detected 1 by a flame atomic absorption method.

And (3) inspecting the sample 1, and determining the silver content of the sample 1 by adopting an atomic absorption spectrometer SavantAA as a determination instrument.

The testing steps are as follows: accurately weighing 1.0000g of sample in a 100ml beaker, wetting with a small amount of water, adding 15ml of hydrochloric acid, heating and decomposing at low temperature for 5min, adding 10ml of nitric acid, continuously heating until the sample is nearly dry (the sample contains carbon, adding 3ml of perchloric acid, heating until dense smoke appears, adding 3ml of nitric acid, heating until the carbon is completely oxidized and steaming until the sample is nearly dry), taking down and cooling, washing the surface and the cup wall with water, adding 15ml of hydrochloric acid and 30ml of water, heating and boiling to dissolve salts, taking down and cooling to room temperature, transferring into a 50ml volumetric flask, diluting with water to scale, uniformly mixing, and clarifying. The absorbance of silver was measured using an air acetylene-flame at a wavelength of 328.1nm of the atomic absorption spectrometer, zeroed with water.

The instrument conditions were as follows:

wavelength: 328.1nm burner height: 5.0 mm; spectral passband: 0.4n m; air flow rate: 6.0L/min; light source: a silver hollow cathode lamp (lamp current 5-10 mA); air-acetylene flame acetylene flow: 1.0L/min.

The experimental results are as follows: the final measured concentration of silver ions of sample 1 was 5200 ppm.

The currently accepted atomic absorption method has higher accuracy, but the method needs expensive experimental equipment and has higher requirements on experimenters, and is not suitable for being mastered and applied by small and medium-sized enterprises. The method for detecting the full-valence silver ions provided by the invention can realize the detection of the full-valence silver ions only by a conventional titration device without expensive experimental equipment, has high detection accuracy, and is very suitable for the quality control standard of self-built products of small and medium-sized enterprises. It should be noted that the concentration of silver ions measured in example 1 was 5100ppm, which is close to the atomic absorption method, and the difference between the two is within the allowable error range of the experimental operation.

Comparative example 2: the silver content of the sample was directly titrated by the verhater method.

Directly titrating monovalent silver ions in the silver solution to be measured by adopting a Flohard method, and adding 0.1mL of ammonium ferric sulfate { NH }₄Fe(SO₄)₂And 0.05mol/L of potassium thiocyanate standard solution is used as a titrant. When the potassium thiocyanate standard solution was added dropwise, a white precipitate of AgSCN was first produced. After the Ag + ions are quantitatively precipitated, one drop of excess potassium thiocyanate standard solution and Fe in the indicator³⁺Ion combination to generate red complex ion [ FeSCN]²⁺When the end point of the titration is reached. The mL of potassium thiocyanate standard solution consumed was recorded at 30 mL.

The finally measured concentration of the silver ions of the sample 1 is 1000ppm, and referring to the measurement result in the comparative example 1, it can be found that the measured content is not more than 20% of the actual content by directly titrating by using the verhath method, and thus, for a sample with unknown silver state, the accurate result cannot be obtained by directly titrating the sample by using the verhath method.

Description of the drawings: sample 1 was obtained from JDTKS-007, Inc. of Jinda nanotechnology (Xiamen).

The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.

It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. The invention is not described in detail in order to avoid unnecessary repetition.

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.

Claims

1. A method for testing the content of silver in a full valence state is characterized by comprising the following steps: the method for testing the content of the full-valence silver comprises the following steps:

step (2): calibrating the titer f of a potassium thiocyanate standard solution

And (3): conversion of silver solution to be tested

2. The method for testing the content of silver in a full valence state according to claim 1, wherein: ag exists in the silver solution to be detected⁰、Ag⁺、Ag²⁺Or Ag³⁺At least one of;

3. The method for testing the content of silver in a full valence state according to claim 1, wherein: the silver standard solution in the step (1) is prepared by adopting 99.99 wt% of pure silver powder, adding concentrated nitric acid for heating until silver is dissolved, cooling, and adding deionized water, and preferably, the concentration of Ag & lt + & gt in the silver standard solution is 0.1-2 g/L.

4. The method for testing the content of silver in a full valence state according to claim 1, wherein: in the step (1), the ammonium ferric sulfate indicator is prepared by adding ammonium ferric sulfate into deionized water for dissolving, and then adjusting to light red with concentrated nitric acid for disappearance, preferably, the mass concentration of the ammonium ferric sulfate in the ammonium ferric sulfate indicator is 50-100 g/L.

5. The method for testing the content of silver in a full valence state according to any one of claims 1 to 4, wherein: in the step (3), the acidic solution is an inorganic acid, preferably at least one of nitric acid, sulfuric acid and hydrochloric acid.

6. The method for testing the content of silver in a full valence state according to any one of claims 1 to 4, wherein: in step (3), the pH is adjusted to 1-6.5.

7. The method for testing the content of silver in a full valence state according to any one of claims 1 to 4, wherein: in the step (3), the strong reducing agent is at least one of borohydride, hydrazine hydrate or sulfide.

8. The method for testing the content of silver in a full valence state according to any one of claims 1 to 4, wherein: and (3) the molar ratio of the estimated silver content in the silver solution to be detected to the consumption of the strong reducing agent is 1:10-1: 20.

9. The method for testing the content of silver in a full valence state according to any one of claims 1 to 4, wherein: and (3) the filter residue is at least one of black filter residue, brown filter residue and white filter residue.

10. The method for testing the content of silver in a full valence state according to any one of claims 1 to 4, wherein: molar equivalent of concentrated nitric acid in the polytetrafluoroethylene container in the step (3): the molar equivalent of the filter residue is 2:1-6: 1;