Needle filter, method for cleaning thereof and pickling solution

Abstract

The application relates to a needle filter and a cleaning method and an acid cleaning solution for cleaning a polytetrafluoroethylene (PTFE) membrane in the needle filter, wherein the acid cleaning solution comprises 0.5-2.5% of nitric acid, 0.5-1.5% of hydrochloric acid, 0.5-2.5% of hydrofluoric acid and the balance of water in percentage by mass. The needle filter cleaned by the acid cleaning solution and the cleaning method has a metal background in the PTFE membrane within 20 mu g / L, is suitable for inorganic trace analysis, and the composition of the acid cleaning solution and the cleaning process are low in cost.

Description

Technical Field

[0001] This application relates to the field of inorganic analysis technology, specifically to a needle filter with low metal background, its cleaning method, and an acid washing solution. Background Technology

[0002] Trace analysis refers to the analysis of analytes at concentration levels in micrograms per liter or kilogram. Trace analysis has very important applications in modern science and technology, especially in high-end manufacturing, precision medical diagnostics, and semiconductor manufacturing.

[0003] Trace analysis is generally divided into organic trace analysis and inorganic trace analysis. As the name suggests, inorganic trace analysis mainly analyzes inorganic elements in samples. Because the content of the inorganic elements being measured in the sample is very low, in order to ensure the accuracy of trace detection results, it is necessary to strictly control each step and influencing factor in the detection process, especially the reagents and consumables used in the detection. There must be strict control and limit requirements on their background levels; otherwise, the accuracy of the results will be directly affected.

[0004] Needle filters are commonly used, fast, convenient, and reliable sample filtration consumables in analytical testing. Because they are disposable, they do not require membrane replacement or cleaning, saving time in sample analysis. In inorganic trace analysis, where it is necessary to filter strong acids and alkalis from inorganic solutions, the needle filter membrane is typically made of acid and alkali resistant polytetrafluoroethylene (PTFE).

[0005] Currently, Agilent Technologies' products hold a dominant position in the inorganic trace analysis market due to their ultra-low metal background in PTFE syringe filters. No domestic manufacturer can currently provide PTFE syringe filters with the same low metal background as Agilent. Summary of the Invention

[0006] The purpose of this application is to provide a new PTFE needle filter with low metal background that can meet the needs of inorganic trace detection.

[0007] To achieve the above objectives, this application provides a pickling solution for a needle filter, wherein the pickling solution is used to clean the polytetrafluoroethylene membrane in the needle filter, and comprises, by mass percentage: Nitric acid 0.5~2.5% Hydrochloric acid 0.5~1.5% Hydrofluoric acid 0.5~2.5% Water balance.

[0008] Preferably, the pickling solution comprises, by mass percentage: Nitric acid 1~2% 1% hydrochloric acid hydrofluoric acid 1~2% Water balance.

[0009] More preferably, the nitric acid, the hydrochloric acid, the hydrofluoric acid, and the water are all of grade G5.

[0010] This application also provides a method for cleaning a needle filter, comprising the following steps: S1. Prepare the pickling solution described in any of the preceding items; S2. Place the needle filter to be cleaned in the pickling solution, stir and soak, then remove the pickling solution. Repeat the cleaning process 1 to 3 times. S3. Rinse the needle filter that has been acid-washed in step S2 with water until the pH of the water is between 6 and 7; In step S2, the number of needle filters cleaned by each liter of the pickling solution does not exceed 100.

[0011] Preferably, in step S2, the needle filter is stirred and soaked in the pickling solution for 10-25 minutes.

[0012] More preferably, step S3 is: placing the needle filter that has been acid-washed in step S2 into the water, stirring and soaking for 10-25 minutes, then removing the water, and washing a total of 4-6 times.

[0013] Preferably, in step S3, the number of needle filters cleaned with every two liters of water does not exceed 100.

[0014] More preferably, the water in step S3 is of grade G5.

[0015] Preferably, the needle filter obtained by cleaning in step S3 is placed in a Class 100 fume hood and dried with nitrogen.

[0016] This application also provides a needle filter, which is obtained by cleaning by any of the cleaning methods described above.

[0017] The technical solution claimed in this application achieves the following beneficial effects: The needle filter obtained by the pickling solution and cleaning method of this application has a metal background of PTFE membrane of less than 20 μg / L, which is comparable to imported products. It is suitable for inorganic trace analysis, and the composition of the pickling solution and the cost of the cleaning process are low, providing more options for the domestic market. Detailed Implementation

[0018] To make the objectives, technical solutions, and beneficial effects of the embodiments in this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] The main chemical reagents used in this section and related information are shown in the table below:

[0020] <Example 1> This embodiment provides a cleaning method for a PTFE needle filter with low metal background and a needle filter obtained by the method. The method is carried out according to the following steps: S1. Preparation of pickling solution: Weigh 14.7g of electronic grade G5 68% nitric acid, 27.0g of 37% concentrated hydrochloric acid, and 20.8g of 48% hydrofluoric acid, respectively, and dissolve them in 937.5g of electronic grade G5 water to obtain a mixed acid solution of 1% nitric acid, 1% hydrochloric acid, and 1% hydrofluoric acid. S2. Pickling: Take 50 commercially available PTFE needle filters to be cleaned, place them in the mixed acid solution prepared above, fully immerse them, stir and soak for 15 minutes, and then remove the solution; Repeat the above cleaning steps, cleaning a total of 2 times; S3. Cleaning: After acid washing, place the obtained PTFE needle filter in 2L of electronic grade G5 water, fully immerse it, stir and soak for 15 minutes, and then remove the solution. Repeat the above cleaning steps for a total of 4 times until the pH of the water is between 6 and 7; After washing, the needle filter is placed in a Class 100 fume hood and dried with nitrogen to obtain a PTFE needle filter with low metal background.

[0021] <Example 2> This embodiment provides a cleaning method for a PTFE needle filter with low metal background and a needle filter obtained by the method. The method is carried out according to the following steps: S1. Preparation of pickling solution: Weigh 29.4g of electronic grade G5 68% nitric acid, 27.0g of 37% concentrated hydrochloric acid, and 41.6g of 48% hydrofluoric acid, respectively, and dissolve them in 902g of electronic grade G5 water to obtain a mixed acid solution of 2% nitric acid, 1% hydrochloric acid, and 2% hydrofluoric acid. S2. Pickling: Take 100 commercially available PTFE needle filters to be treated, place them in the mixed acid solution prepared above, fully immerse them, stir and soak for 20 minutes, and then remove the solution; Repeat the above cleaning steps, cleaning a total of 2 times; S3. Cleaning: After acid washing, place the obtained PTFE needle filter in 2L of electronic grade G5 water, fully immerse it, stir and soak for 20 minutes, and then remove the solution. Repeat the above cleaning steps for a total of 6 times until the pH of the water is between 6 and 7; After washing, the needle filter is placed in a Class 100 fume hood and dried with nitrogen to obtain a PTFE needle filter with low metal background.

[0022] <Comparative Example 1> This comparative example provides a cleaning method for a PTFE needle filter and a needle filter obtained by the method. The method is carried out according to the following steps: S1. Preparation of pickling solution: Weigh 44.1g of electronic grade G5 68% nitric acid and dissolve it in 955.9g of electronic grade G5 water to obtain a 3% nitric acid solution; S2. Pickling: Take 50 commercially available PTFE needle filters to be treated, place them in the mixed acid solution prepared above, fully immerse them, stir and soak for 20 minutes, and then remove the solution; Repeat the above cleaning steps, cleaning a total of 2 times; S3. Cleaning: After acid washing, place the obtained PTFE needle filter in 2L of electronic grade G5 water, fully immerse it, stir and soak for 20 minutes, and then remove the solution. Repeat the above cleaning steps for a total of 5 times until the pH of the water is between 6 and 7; After washing, the needle filter is placed in a Class 100 fume hood and dried with nitrogen to obtain a PTFE needle filter.

[0023] <Comparative Example 2> This comparative example provides a cleaning method for a PTFE needle filter and a needle filter obtained by the method. The method is carried out according to the following steps: S1. Preparation of pickling solution: Weigh 27.0g of 37% concentrated hydrochloric acid of electronic grade G5 and dissolve it in 973g of electronic grade G5 water to obtain a 1% hydrochloric acid solution; S2. Pickling: Take 50 commercially available PTFE needle filters to be treated, place them in the mixed acid solution prepared above, fully immerse them, stir and soak for 20 minutes, and then remove the solution; Repeat the above cleaning steps, cleaning a total of 2 times; S3. Cleaning: After acid washing, place the obtained PTFE needle filter in 2L of electronic grade G5 water, fully immerse it, stir and soak for 20 minutes, and then remove the solution. Repeat the above cleaning steps for a total of 5 times until the pH of the water is between 6 and 7; After washing, the needle filter is placed in a Class 100 fume hood and dried with nitrogen to obtain a PTFE needle filter.

[0024] <Comparative Example 3> This comparative example provides a cleaning method for a PTFE needle filter and a needle filter obtained by the method. The method is carried out according to the following steps: S1. Preparation of pickling solution: Weigh 41.6g of electronic grade G5 48% hydrofluoric acid and dissolve it in 958.4g of electronic grade G5 water to obtain a 2% hydrofluoric acid solution; S2. Pickling: Take 50 commercially available PTFE needle filters to be treated, place them in the mixed acid solution prepared above, fully immerse them, stir and soak for 20 minutes, and then remove the solution; Repeat the above cleaning steps, cleaning a total of 2 times; S3. Cleaning: After acid washing, place the obtained PTFE needle filter in 2L of electronic grade G5 water, fully immerse it, stir and soak for 20 minutes, and then remove the solution. Repeat the above cleaning steps for a total of 5 times until the pH of the water is between 6 and 7; After washing, the needle filter is placed in a Class 100 fume hood and dried with nitrogen to obtain a PTFE needle filter.

[0025] <Comparative Example 4> This comparative example provides a cleaning method for a PTFE needle filter and a needle filter obtained by the method. The method is carried out according to the following steps: S1. Preparation of pickling solution: Weigh 14.7g of 68% nitric acid and 27.0g of 37% concentrated hydrochloric acid of electronic grade G5, respectively, and dissolve them in 958.3g of electronic grade G5 water to obtain a mixed acid solution of 1% nitric acid and 1% hydrochloric acid; S2. Pickling: Take 50 commercially available PTFE needle filters to be treated, place them in the mixed acid solution prepared above, fully immerse them, stir and soak for 15 minutes, and then remove the solution; Repeat the above cleaning steps, cleaning a total of 2 times; S3. Cleaning: After acid washing, place the obtained PTFE needle filter in 2L of electronic grade G5 water, fully immerse it, stir and soak for 15 minutes, and then remove the solution. Repeat the above cleaning steps for a total of 4 times until the pH of the water is between 6 and 7; After washing, the needle filter is placed in a Class 100 fume hood and dried with nitrogen to obtain a PTFE needle filter.

[0026] <Comparative Example 5> This comparative example provides a cleaning method for a PTFE needle filter and a needle filter obtained by the method. The method is carried out according to the following steps: S1. Preparation of pickling solution: Weigh 14.7g of 68% nitric acid and 20.8g of 48% hydrofluoric acid of electronic grade G5, respectively, and dissolve them in 964.5g of electronic grade G5 water to obtain a mixed acid solution of 1% nitric acid and 1% hydrofluoric acid; S2. Pickling: Take 50 commercially available PTFE needle filters to be treated, place them in the mixed acid solution prepared above, fully immerse them, stir and soak for 15 minutes, and then remove the solution; Repeat the above cleaning steps, cleaning a total of 2 times; S3. Cleaning: After acid washing, place the obtained PTFE needle filter in 2L of electronic grade G5 water, fully immerse it, stir and soak for 15 minutes, and then remove the solution. Repeat the above cleaning steps for a total of 4 times until the pH of the water is between 6 and 7; After washing, the needle filter is placed in a Class 100 fume hood and dried with nitrogen to obtain a PTFE needle filter.

[0027] <Comparative Example 6> This comparative example provides a cleaning method for a PTFE needle filter and a needle filter obtained by the method. The method is carried out according to the following steps: S1. Preparation of pickling solution: Weigh 27.0g of 37% concentrated hydrochloric acid and 20.8g of 48% hydrofluoric acid of electronic grade G5, respectively, and dissolve them in 952.2g of electronic grade G5 water to obtain a mixed acid solution of 1% hydrochloric acid and 1% hydrofluoric acid; S2. Pickling: Take 50 commercially available PTFE needle filters to be treated, place them in the mixed acid solution prepared above, fully immerse them, stir and soak for 15 minutes, and then remove the solution; Repeat the above cleaning steps, cleaning a total of 2 times; S3. Cleaning: After acid washing, place the obtained PTFE needle filter in 2L of electronic grade G5 water, fully immerse it, stir and soak for 15 minutes, and then remove the solution. Repeat the above cleaning steps for a total of 4 times until the pH of the water is between 6 and 7; After washing, the needle filter is placed in a Class 100 fume hood and dried with nitrogen to obtain a PTFE needle filter.

[0028] <Comparative Example 7> This comparative example provides a cleaning method for a PTFE needle filter and a needle filter obtained by the method. The method is carried out according to the following steps: S1. Preparation of pickling solution: Weigh out 29.4g of electronic grade G5 68% nitric acid and 37% concentrated hydrochloric acid respectively. 27.0g of 48% hydrofluoric acid and 41.6g of hydrofluoric acid were dissolved in 902g of electronic grade G5 water to obtain a mixed acid solution of 2% nitric acid, 1% hydrochloric acid and 2% hydrofluoric acid. S2. Pickling: Take 120 commercially available PTFE needle filters to be treated, place them in the mixed acid solution prepared above, fully immerse them, stir and soak for 20 minutes, and then remove the solution; Repeat the above cleaning steps, cleaning a total of 2 times; S3. Cleaning: After acid washing, place the obtained PTFE needle filter in 2L of electronic grade G5 water, fully immerse it, stir and soak for 20 minutes, and then remove the solution. Repeat the above cleaning steps for a total of 6 times until the pH of the water is between 6 and 7; After washing, the needle filter is placed in a Class 100 fume hood and dried with nitrogen to obtain a PTFE needle filter.

[0029] <Comparative Example 8> This comparative example provides a cleaning method for a PTFE needle filter and a needle filter obtained by the method. The method is carried out according to the following steps: S1. Preparation of pickling solution: Weigh 14.7g of electronic grade G5 68% nitric acid, 27.0g of 37% concentrated hydrochloric acid, and 20.8g of 48% hydrofluoric acid, respectively, and dissolve them in 937.5g of electronic grade G5 water to obtain a mixed acid solution of 1% nitric acid, 1% hydrochloric acid, and 1% hydrofluoric acid. S2. Pickling: Take 50 commercially available PTFE needle filters to be treated, place them in the mixed acid solution prepared above, fully immerse them, stir and soak for 15 minutes, and then remove the solution; S3. Cleaning: After acid washing, place the obtained PTFE needle filter in 2L of electronic grade G5 water, fully immerse it, stir and soak for 15 minutes, and then remove the solution. Repeat the above cleaning steps for a total of 4 times until the pH of the water is between 6 and 7; After washing, the needle filter is placed in a Class 100 fume hood and dried with nitrogen to obtain a PTFE needle filter.

[0030] <Comparative Example 9> This comparative example provides a cleaning method for a PTFE needle filter and a needle filter obtained by the method. The method is carried out according to the following steps: S1. Preparation of pickling solution: Weigh 73.5g of 68% nitric acid (electronic grade G5), 135.0g of 37% concentrated hydrochloric acid, and 104.0g of 48% hydrofluoric acid, respectively, and dissolve them in 687.5g of electronic grade G5 water to obtain a mixed acid solution of 5% nitric acid, 5% hydrochloric acid, and 5% hydrofluoric acid. S2. Pickling: Take 50 commercially available PTFE needle filters to be treated, place them in the mixed acid solution prepared above, fully immerse them, stir and soak for 15 minutes, and then remove the solution; S3. Cleaning: After acid washing, place the obtained PTFE needle filter in 2L of electronic grade G5 water, fully immerse it, stir and soak for 15 minutes, and then remove the solution. Repeat the above cleaning steps for a total of 4 times until the pH of the water is between 6 and 7; After washing, the needle filter is placed in a Class 100 fume hood and dried with nitrogen to obtain a PTFE needle filter.

[0031] <Test Example 1> This test example tests the metal background of the PTFE membrane in the PTFE needle filters of Examples 1-2 and Comparative Examples 1-9.

[0032] The experimental reagents used in this test case are as follows: Electronic grade G5 68% nitric acid (w / w), ultrapure water, and standard solutions of 65 elements (Li, Be, Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi).

[0033] This test case is performed according to the following steps: Weigh 15.4g of electronic grade G5 68% nitric acid and dissolve it in 989g of ultrapure water to obtain 1% nitric acid (w / w) for later use; Sixty-five elemental standards were prepared in groups based on the mutual interference between elements and the properties of the standard solutions. They were prepared into mixed standards of 1000 μg / L, 500 μg / L, 250 μg / L, 100 μg / L and 10 μg / L using ultrapure water, and then injected sequentially from low concentration to high concentration on ICP-MS to establish standard curves for the target elements. Take 1% nitric acid solution and pass it through a needle filter at a rate of 0.5 s / drop. Collect the first 1.5 mL of filtrate in a sample vial and detect it on an ICP-MS. Calculate the background concentration of the metal based on the standard curve.

[0034] The test results are shown in Table 1.

[0035] Table 1. Total metal background of each needle filter Example 1 19.90 Example 2 8.22 Comparative Example 1 188.65 Comparative Example 2 273.46 Comparative Example 3 229.13 Comparative Example 4 105.73 Comparative Example 5 136.42 Comparative Example 6 109.13 Comparative Example 7 85.38 Comparative Example 8 78.61 Comparative Example 9 6.20 Untreated PTFE needle filter 511.83 Agilent PTFE needle filter 17.16 As shown in Table 1, after acid cleaning using the methods of Examples 1 and 2, the total metal background of the conventional PTFE needle filter can be reduced from an initial 511.83 μg / L to below 20 μg / L, indicating that the effect of acid cleaning is comparable to imported needle filter products. However, if a single acid or only two acids are used for acid cleaning (i.e., the methods in Comparative Examples 1-6), the total metal background of the cleaned needle filter remains high, ranging from 109.13 to 273.46 μg / L. Furthermore, if too many filters are added to a given amount of acid cleaning solution or too few cleaning cycles are performed, the total metal background of the cleaned needle filter remains high, failing to reach the target value of below 20 μg / L. While Comparative Example 9 achieved a low total metal background by reducing the number of cleaning cycles, the acid concentration in the cleaning solution was too high.

[0036] <Test Example 2> This test example performs bubble point tests on the PTFE membranes of the needle filters in Examples 1-2 and Comparative Examples 1-9.

[0037] The experimental reagent used in this test case is ultrapure water.

[0038] This test case is performed according to the following steps: After drawing 5 mL of ultrapure water with a syringe and connecting it to the needle filter, slowly press the syringe plunger to fully wet the filter membrane in the needle filter. After wetting the needle filter, correctly install it onto the interface of the filter bubble point test device, and connect the hose to the outlet of the needle filter. Set the instrument parameters and start the test. When you observe a series of stable bubbles emerging from the tubing, pause the instrument pressurization. This is the bubble point pressure of the needle filter.

[0039] The test results are shown in Table 2.

[0040] Table 2. Bubble point pressure of various needle filters Example 1 36.8 Example 2 40.2 Comparative Example 1 29.5 Comparative Example 2 33.7 Comparative Example 3 41.8 Comparative Example 4 28.4 Comparative Example 5 30.9 Comparative Example 6 43.4 Comparative Example 7 32.0 Comparative Example 8 38.8 Comparative Example 9 11.0 Untreated PTFE needle filter 34.1 The normal bubble point pressure range for hydrophilic PTFE filters is between 20 and 50 psi. As shown in Table 2, after acid cleaning, the bubble point pressures of the PTFE membranes in Examples 1-2 and Comparative Examples 1-8 are within the normal range, indicating that the filter membranes were not damaged after acid immersion cleaning and can achieve normal filtration. However, the filter in Comparative Example 9, due to immersion in excessively concentrated acid, suffered acid corrosion and damage to the filter membrane, resulting in enlarged pores and a bubble point pressure outside the normal range, thus failing to achieve normal filtration. Therefore, the appropriate acid ratio and concentration in the cleaning solution have a significant impact on filter performance.

[0041] The embodiments and application examples described above are merely illustrative descriptions of this application and are not intended to limit the scope of this application. Any modifications and improvements made to the technical solutions of this application by those skilled in the art without departing from the spirit of this application should fall within the protection scope defined by this application.

Claims

1. A pickling solution for a needle filter, characterized in that, The pickling solution is used to clean the polytetrafluoroethylene membrane in the needle filter, and comprises, by mass percentage: Nitric acid 0.5~2.5% Hydrochloric acid 0.5~1.5% Hydrofluoric acid 0.5~2.5% Water balance.

2. The pickling solution according to claim 1, characterized in that, By weight percentage, including: Nitric acid 1~2% 1% hydrochloric acid hydrofluoric acid 1~2% Water balance.

3. The pickling solution according to claim 1, characterized in that, The nitric acid, hydrochloric acid, hydrofluoric acid, and water are all of grade G5.

4. A method for cleaning a needle filter, characterized in that, Includes the following steps: S1. Prepare the pickling solution as described in any one of claims 1 to 3; S2. Place the needle filter to be cleaned in the pickling solution, stir and soak, then remove the pickling solution. Repeat the cleaning process 1 to 3 times. S3. Rinse the needle filter that has been acid-washed in step S2 with water until the pH of the water is between 6 and 7; In step S2, the number of needle filters cleaned by each liter of the pickling solution does not exceed 100.

5. The cleaning method according to claim 4, characterized in that, In step S2, the needle filter is stirred and soaked in the pickling solution for 10-25 minutes.

6. The cleaning method according to claim 4, characterized in that, Step S3 is as follows: Place the needle filter that has been acid-washed in step S2 into the water, stir and soak for 10-25 minutes, then remove the water, and wash it a total of 4-6 times.

7. The cleaning method according to claim 6, characterized in that, In step S3, the number of needle filters cleaned with every two liters of water does not exceed 100.

8. The cleaning method according to claim 4, characterized in that, The water used in step S3 is of grade G5.

9. The cleaning method according to claim 4, characterized in that, The needle filter obtained after cleaning in step S3 is placed in a Class 100 fume hood and dried with nitrogen.

10. A needle filter, characterized in that, Obtained by the cleaning method according to any one of claims 4 to 9.

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