Detection method of hypophosphorous acid and phosphorous acid

Abstract

The invention belongs to the technical field of chemical analysis, and provides a detection method of hypophosphorous acid and phosphorous acid. The invention provides a method for detecting hypophosphorous acid and phosphorous acid, aiming at solving the problem of large error in a method for measuring hypophosphorous acid and phosphorous acid in the prior art. According to the method, sodium hypophosphite monohydrate and sodium phosphite pentahydrate are adopted to prepare hypophosphorous acid and phosphorous acid standard solutions in a gradient manner, and the hypophosphorous acid and phosphorous acid standard solutions are detected by using the detection method according to detection data. According to the detection method for hypophosphorous acid and phosphorous acid, the error rate can be controlled within 15%, and the detection requirement is completely met.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical analysis, and in particular relates to a method for detecting hypophosphorous acid and phosphorous acid. Background Art

[0002] At present, in the electroplating industry, due to the uniform coating characteristics of chemical nickel plating, the use of chemical nickel plating has gradually surpassed that of electroplated nickel. In chemical nickel plating, the ratio of nickel and hypophosphorous acid concentration in the nickel plating bath is crucial. In addition, during the chemical nickel plating process, hypophosphorous acid will gradually oxidize into phosphorous acid. In the nickel plating bath, if the phosphorous acid concentration is too high, it will lead to a series of problems such as decreased bonding strength of the plated parts and decreased plating speed. Therefore, phosphorous acid has become a decisive indicator for the scrapping of the nickel plating bath. According to the on-site measurement of the nickel plating production line, when the phosphorous acid concentration reaches 120g / L or more, the thick plating of engineering parts (chemical nickel plating for 1h) will not be possible; when the phosphorous acid concentration reaches 170g / L or more, the thin plating of engineering parts (chemical nickel plating for 10min) cannot be completed, and the nickel plating bath is completely scrapped.

[0003] At present, there are many detection methods for hypophosphorous acid and phosphorous acid, and the commonly used detection method is iodine titration. However, due to the diversity of detection methods, the detection data error is large, which seriously affects the technical exchanges between enterprises. Therefore, the present invention aims at this problem and improves on the original basis to control the measurement error within 15%. Summary of the invention

[0004] The object of the present invention is to provide a method for detecting hypophosphorous acid and phosphorous acid, so as to solve the problem of large error in the measurement method of hypophosphorous acid and phosphorous acid in the prior art.

[0005] The purpose of the present invention is that the purpose of the present invention can be achieved by the following technical solutions:

[0006] The first aspect of the present invention provides a method for detecting hypophosphorous acid, comprising the following steps:

[0007] Sample to be tested: Use a pipette to transfer the test solution into an iodine volumetric bottle, add hydrochloric acid solution, then add iodine standard solution, clean the bottleneck with hydrochloric acid, cover the bottle stopper and place it in a dark place, keep it at a constant temperature of 20℃~35℃ for more than 30 minutes; open the bottle stopper, wash the bottleneck and bottle stopper with a small amount of distilled water, titrate with Na2S2O3 standard solution until it turns light yellow, add starch indicator, and continue to titrate until the blue color disappears, which is the end point. The volume of Na2S2O3 standard solution consumed is V2;

[0008] Blank sample: Use a pipette to transfer distilled water into an iodine volumetric flask, add hydrochloric acid solution, then add iodine standard solution, clean the bottleneck with hydrochloric acid, cover the bottle stopper and place it in a dark place, keep it at a constant temperature of 20℃~35℃ for more than 30 minutes; open the bottle stopper, wash the bottleneck and bottle stopper with a small amount of distilled water, titrate with Na2S2O3 standard solution until it turns light yellow, add starch indicator, and continue titrating until the blue color disappears, which is the end point. The volume of Na2S2O3 standard solution consumed is taken as V0;

[0009] Standard solution detection: Sodium hypophosphite monohydrate is used to prepare the standard solution. According to its molar mass, 10g / L, 20g / L, 30g / L, and 40g / L hypophosphorous acid standard solutions are prepared respectively. The detection value is calculated by directly substituting the V2 value into the formula. The correction value is calculated by converting the sodium thiosulfate consumption value of the blank sample into the V2′ value and substituting it into the formula. Finally, the concentration of hypophosphorous acid is calculated by substituting it into the formula.

[0010] Further, the concentration of hypophosphorous acid is calculated as follows:

[0011]

[0012] Where: C1—concentration of iodine standard solution, mol / L;

[0013] Note: Equivalent to C(I2) = 0.05 mol / L;

[0014] V1—the volume of the iodine standard solution used, mL;

[0015] C2—concentration of sodium thiosulfate standard solution, mol / L;

[0016] V2—the volume of sodium thiosulfate standard solution consumed by the test solution, mL;

[0017] V0—the volume of sodium thiosulfate standard solution consumed in the blank, mL;

[0018] V2′—the volume of sodium thiosulfate standard solution consumed by the test solution after correction, mL;

[0019] V3—volume to be measured, mL;

[0020] 66—Molecular weight of hypophosphorous acid.

[0021] Furthermore, the calculation formula of V2′ is:

[0022]

[0023] Furthermore, the purity of sodium hypophosphite monohydrate is ≥98%.

[0024] A second aspect of the present invention provides a method for detecting phosphorous acid, comprising the following steps:

[0025] Sample to be tested: Use a pipette to transfer the test solution into an iodine volumetric bottle; add distilled water, sodium bicarbonate solution, and then iodine standard solution, cover the bottle stopper and place it in a dark place, and keep it at a constant temperature of 20℃~35℃ for more than 1h; open the bottle stopper, adjust the pH with acetic acid, shake well to allow the gas to escape completely, titrate with Na2S2O3 standard solution until it turns light yellow, add starch indicator, and continue titrating until the blue color disappears, which is the end point. The volume of Na2S2O3 standard solution consumed is taken as V2;

[0026] Blank sample: Use a pipette to transfer distilled water into an iodine volumetric bottle; add distilled water, sodium bicarbonate solution, and then iodine standard solution, cover the bottle stopper and place it in a dark place, and keep it at a constant temperature of 20℃~35℃ for more than 1 hour; open the bottle stopper, adjust the pH with acetic acid, shake well to allow the gas to escape completely, titrate with Na2S2O3 standard solution until light yellow, add starch indicator, and continue titrating until the blue color disappears, which is the end point. The volume of Na2S2O3 standard solution consumed is V2;

[0027] Standard solution detection: Sodium phosphite pentahydrate was used to prepare the standard solution. According to its molar mass, 10g / L, 20g / L, and 30g / L phosphorous acid standard solutions were prepared respectively. The detection value was calculated by directly substituting the V2 value into the formula. The correction value was calculated by converting the sodium thiosulfate consumption value of the blank sample into the V2′ value and substituting it into the formula. Finally, the concentration of phosphorous acid was calculated by substituting it into the formula.

[0028] Further, the concentration of phosphorous acid is calculated as follows:

[0029]

[0030] Where: C1—concentration of iodine standard solution, mol / L;

[0031] Note: Equivalent to C(I2) = 0.05 mol / L;

[0032] V1—the volume of the iodine standard solution used, mL;

[0033] C2—concentration of sodium thiosulfate standard solution, mol / L;

[0034] V2—the volume of sodium thiosulfate standard solution consumed by the test solution, mL;

[0035] V0—the volume of sodium thiosulfate standard solution consumed in the blank, mL;

[0036] V2′—the volume of sodium thiosulfate standard solution consumed by the test solution after correction, mL;

[0037] V3—volume to be measured, mL;

[0038] 82—Molecular weight of phosphorous acid.

[0039] Furthermore, the calculation formula of V2′ is:

[0040]

[0041] Furthermore, the pH in the test sample and blank sample steps is adjusted to: pH < 4.

[0042] Furthermore, the purity of sodium phosphite pentahydrate is ≥98%.

[0043] Beneficial effects of the present invention:

[0044] The present invention uses sodium hypophosphite monohydrate and sodium phosphite pentahydrate reagents to prepare hypophosphorous acid and phosphorous acid standard solutions in stages, and uses the detection method to detect them. According to the detection data, the detection method for hypophosphorous acid and phosphorous acid provided by the present invention can control the error rate within 15%, which fully meets the detection requirements. DETAILED DESCRIPTION

[0045] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] Example 1

[0047] This embodiment provides a method for detecting hypophosphorous acid, comprising the following steps:

[0048] The hypophosphorous acid detection principle is:

[0049] In an acidic solution, add excess I2 to oxidize H2PO2, and then back-titrate the excess I2 with a Na2S2O3 (sodium thiosulfate) standard solution. Using starch as an indicator, titrate with a Na2S2O3 standard solution until it becomes colorless, which is the reaction endpoint.

[0050] (1) Sample to be tested:

[0051] Use a pipette to transfer 2mL of the test solution into a 250mL iodine volumetric flask, add 25mL of hydrochloric acid solution (the volume ratio of hydrochloric acid to water is 1:1), then add 25mL of 0.1mol / L iodine standard solution, wash the bottleneck with 3-5mL of hydrochloric acid, cover the bottle stopper and place it in a dark place, keep it at a constant temperature of 20℃-35℃ for 30min; open the bottle stopper, wash the bottleneck and bottle stopper with a small amount of distilled water, titrate with Na2S2O3 standard solution until it turns light yellow, add 3mL of 1% starch indicator, and continue to titrate until the blue disappears, which is the end point. The volume of Na2S2O3 standard solution consumed is taken as V2;

[0052] (2) Blank sample:

[0053] Use a pipette to transfer 2mL of distilled water into a 250mL iodine volumetric flask, add 25mL of hydrochloric acid solution (the volume ratio of hydrochloric acid to water is 1:1), then add 25mL of 0.1mol / L iodine standard solution, wash the bottleneck with 3-5mL of hydrochloric acid, cover the bottle stopper and place it in a dark place, and keep it at a constant temperature of 20℃-35℃ for about 30min; open the bottle stopper, wash the bottleneck and bottle stopper with a small amount of distilled water, titrate with Na2S2O3 standard solution until it turns light yellow, add 3mL of 1% starch indicator, and continue to titrate until the blue color disappears, which is the end point. The volume of Na2S2O3 standard solution consumed is taken as V0.

[0054] Calculation formula:

[0055] Where: C1—concentration of iodine standard solution, 0.05 mol / L;

[0056] Note: Equivalent to C(I2) = 0.05 mol / L;

[0057] V1—the volume of the iodine standard solution used, 25 mL;

[0058] C2—concentration of sodium thiosulfate standard solution, 0.1 mol / L;

[0059] V2—the volume of sodium thiosulfate standard solution consumed by the test solution, mL;

[0060] V0—the volume of sodium thiosulfate standard solution consumed in the blank, mL;

[0061] V2′—the volume of sodium thiosulfate standard solution consumed by the test solution after correction, mL;

[0062]

[0063] V3—volume to be measured, 2mL;

[0064] 66—Molecular weight of hypophosphorous acid.

[0065] (3) Standard solution detection:

[0066] Sodium hypophosphite monohydrate (purchased from Sinopharm Chemical Reagent Co., Ltd.) was used to prepare the standard solution. 10 g / L, 20 g / L, 30 g / L, and 40 g / L hypophosphorous acid standard solutions were prepared according to their molar mass. The test value was calculated by directly substituting the V2 value into the formula. The correction value was calculated by converting the sodium thiosulfate consumption value of the blank sample into the V2' value and substituting it into the formula. The specific test results are shown in Table 1:

[0067] Table 1

[0068] project Detection value Error rate Correction value Error rate 10g / L Hypophosphorous acid standard solution 15.01g / L 50.1％ 11.44g / L 14.4％ 20g / L Hypophosphorous acid standard solution 23.93g / L 19.7％ 21.56g / L 7.8％ 30g / L Hypophosphorous acid standard solution 33.17g / L 10.6％ 32.06g / L 6.9％ 40g / L Hypophosphorous acid standard solution 37.78g / L 5.6％ 37.31g / L 6.7％

[0069] When V1=25mL, the upper limit of hypophosphorous acid measurement is 41.25g / L. According to the data in the table above, it can be seen that directly using V2 for calculation will result in large errors, especially for the detection value of hypophosphorous acid concentration between 0 and 20g / L. However, by titrating the blank, V2 is multiplied by an adjustment coefficient to obtain V2', and the V2' value is substituted into the formula for calculation to obtain the correction value. It can be seen from the table above that the error coefficient of the correction value is controlled within 15%.

[0070] At present, the concentration of hypophosphorous acid in nickel aging solution is between 10g / L and 30g / L. Considering the error rate of the comprehensive correction value, it is more appropriate to choose 25mL of V1 dosage.

[0071] (4) Error cause analysis:

[0072] Theoretically, during blank titration, the V1 value (iodine solution volume) should be equal to the V0 value (sodium thiosulfate titration volume). However, since both the iodine solution and the sodium thiosulfate standard solution are substances that are easily decomposed by light, and there may be certain impurities in the prepared hydrochloric acid solution, this will cause V1≠V0. Therefore, to address this phenomenon, a blank sample should be added to each experiment, and the sodium thiosulfate consumption value V2 of the sample to be tested multiplied by V1 / V0 is used as the correction value of the sodium thiosulfate of the sample to be tested and substituted into the formula for calculation, thereby reducing measurement errors.

[0073] Example 2

[0074] This embodiment provides a method for detecting phosphorous acid, comprising the following steps:

[0075] The phosphorous acid detection principle is:

[0076] In sodium bicarbonate solution, I2 can quickly oxidize H3PO3, while H2PO2 hardly participates in the reaction. Therefore, excess I2 is added to react with H3PO3, and the excess I2 is back-titrated with Na2S2O3 (sodium thiosulfate) standard solution, using starch solution as an indicator.

[0077] (1) Sample to be tested:

[0078] Use a pipette to transfer 3 mL of the test solution into a 250 mL iodine volumetric flask; add 40 mL of distilled water, add 25 mL of 50 g / L sodium bicarbonate solution, and then add 25 mL of 0.1 mol / L iodine standard solution, cover the bottle stopper and place it in a dark place, and keep it at a constant temperature of 20°C to 35°C for 1 hour; open the bottle stopper, adjust the pH to less than 4 with acetic acid (add 3 mL of acetic acid), shake well to allow the gas to escape completely, titrate with Na2S2O3 standard solution to light yellow, add 3 mL of 1% starch indicator, and continue to titrate until the blue color disappears, which is the end point. The volume of Na2S2O3 standard solution consumed is taken as V2;

[0079] (2) Blank sample:

[0080] Use a pipette to transfer 3 mL of distilled water into a 250 mL iodine volumetric flask; add 40 mL of distilled water, add 25 mL of 50 g / L sodium bicarbonate solution, and then add 25 mL of 0.1 mol / L iodine standard solution, cover the bottle stopper and place it in a dark place, and keep it at a constant temperature of 20°C to 35°C for 1 hour; open the bottle stopper, adjust the pH to less than 4 with acetic acid (add 3 mL of acetic acid), shake well to allow the gas to escape completely, titrate with Na2S2O3 standard solution to light yellow, add 3 mL of 1% starch indicator, and continue to titrate until the blue color disappears, which is the end point, and the volume of Na2S2O3 standard solution consumed is taken as V2;

[0081] Calculation formula:

[0082] Where: C1—concentration of iodine standard solution, 0.05 mol / L;

[0083] Note: Equivalent to C(I2) = 0.05 mol / L;

[0084] V1—the volume of the iodine standard solution used, 25 mL;

[0085] C2—concentration of sodium thiosulfate standard solution, 0.1 mol / L;

[0086] V2—the volume of sodium thiosulfate standard solution consumed by the test solution, mL;

[0087] V0—the volume of sodium thiosulfate standard solution consumed in the blank, mL;

[0088] V2′—the volume of sodium thiosulfate standard solution consumed by the test solution after correction, mL;

[0089]

[0090] V3—volume to be measured, 3mL;

[0091] 82—Molecular weight of phosphorous acid.

[0092] (3) Standard solution detection:

[0093] Sodium phosphite pentahydrate (purchased from Sinopharm Chemical Reagent Co., Ltd.) was used to prepare the standard solution. According to its molar mass, 10 g / L, 20 g / L, and 30 g / L phosphorous acid standard solutions were prepared respectively. The test value was calculated by directly substituting the V2 value into the formula. The correction value was calculated by converting the sodium thiosulfate consumption value of the blank sample into the V2' value and substituting it into the formula. The specific test results are shown in Table 2:

[0094] Table 2

[0095] project Detection value Error rate Correction value Error rate 10g / L phosphorous acid standard solution 12.3g / L 23.0％ 11.39g / L 13.9％ 20g / L phosphorous acid standard solution 22.55g / L 12.8％ 22.07g / L 10.4％ 30g / L phosphorous acid standard solution 31.16g / L 3.9％ 31.03g / L 3.4％

[0096] When V1=25mL, the upper limit of phosphorous acid measurement is 34.17g / L. According to the data in the table above, it can be seen that directly using V2 for calculation will result in large errors, especially for the detection value of phosphorous acid concentration between 0 and 20g / L. However, by titrating the blank, V2 is multiplied by an adjustment coefficient to obtain V2', and the V2' value is substituted into the formula for calculation to obtain the correction value. It can be seen from the table above that the error coefficient of the correction value is controlled within 15%.

[0097] At present, the concentration of phosphorous acid in nickel aging solution is between 100g / L and 400g / L. The nickel aging solution is diluted 10 times for testing. Considering the error rate of the comprehensive correction value, it is more appropriate to choose 25mL of V1 dosage.

[0098] (4) Error cause analysis:

[0099] When using blank titration, the V1 value (iodine solution volume) should be equal to the V0 value (sodium thiosulfate titration volume). However, since both the iodine solution and the sodium thiosulfate standard solution are substances that are easily decomposed by light, and the prepared sodium bicarbonate solution may contain certain impurities, this will cause V1≠V0. In each experiment, a blank sample is added, and the sodium thiosulfate consumption value V2 of the sample to be tested is multiplied by V1 / V0 as the correction value of the sodium thiosulfate of the sample to be tested and substituted into the formula for calculation, thereby reducing measurement errors.

[0100] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0101] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for detecting hypophosphorous acid, characterized in that, The following steps are involved: Sample to be tested: Use a pipette to transfer the test solution into an iodine volumetric bottle, add hydrochloric acid solution, then add iodine standard solution, clean the bottleneck with hydrochloric acid, cover the bottle stopper and place it in a dark place, keep it at a constant temperature of 20℃~35℃ for more than 30 minutes; open the bottle stopper, wash the bottleneck and bottle stopper with a small amount of distilled water, titrate with Na2S2O3 standard solution until it turns light yellow, add starch indicator, and continue to titrate until the blue color disappears, which is the end point. The volume of Na2S2O3 standard solution consumed is V2; Blank sample: Use a pipette to transfer distilled water into an iodine volumetric flask, add hydrochloric acid solution, then add iodine standard solution, clean the bottleneck with hydrochloric acid, cover the bottle stopper and place it in a dark place, keep it at a constant temperature of 20℃~35℃ for more than 30 minutes; open the bottle stopper, wash the bottleneck and bottle stopper with a small amount of distilled water, titrate with Na2S2O3 standard solution until it turns light yellow, add starch indicator, and continue titrating until the blue color disappears, which is the end point. The volume of Na2S2O3 standard solution consumed is taken as V0; Standard solution detection: Sodium hypophosphite monohydrate is used to prepare the standard solution. According to its molar mass, 10g / L, 20g / L, 30g / L, and 40g / L hypophosphorous acid standard solutions are prepared respectively. The detection value is calculated by directly substituting the V2 value into the formula. The correction value is calculated by converting the sodium thiosulfate consumption value of the blank sample into the V2′ value and substituting it into the formula. Finally, the concentration of hypophosphorous acid is calculated by substituting it into the formula.

2. The method for detecting hypophosphorous acid according to claim 1, characterized in that: The concentration of hypophosphorous acid is calculated as follows: Where: C1—concentration of iodine standard solution, mol / L; Note: Equivalent to C(I2) = 0.05 mol / L; V1—the volume of the iodine standard solution used, mL; C2—concentration of sodium thiosulfate standard solution, mol / L; V2—the volume of sodium thiosulfate standard solution consumed by the test solution, mL; V0—the volume of sodium thiosulfate standard solution consumed in the blank, mL; V2′—the volume of sodium thiosulfate standard solution consumed by the test solution after correction, mL; V3—volume to be measured, mL; 66—Molecular weight of hypophosphorous acid.

3. A method for detecting hypophosphorous acid according to claim 2, characterized in that, The calculation formula of V2′ is:

4. The method for detecting hypophosphorous acid according to claim 1, characterized in that: The purity of sodium hypophosphite monohydrate is ≥98%.

5. A method for detecting phosphorous acid, characterized in that, The following steps are involved: Sample to be tested: Use a pipette to transfer the test solution into an iodine volumetric bottle; Add distilled water, sodium bicarbonate solution, and then iodine standard solution, cover the bottle stopper and place it in a dark place, keep it at a constant temperature of 20℃~35℃ for more than 1h; open the bottle stopper, adjust the pH with acetic acid, shake well to allow the gas to escape completely, titrate with Na2S2O3 standard solution until it turns light yellow, add starch indicator, and continue titrating until the blue color disappears, which is the end point. The volume of Na2S2O3 standard solution consumed is V2; Blank sample: Use a pipette to transfer distilled water into an iodine volumetric bottle; add distilled water, sodium bicarbonate solution, and then iodine standard solution, cover the bottle stopper and place it in a dark place, and keep it at a constant temperature of 20℃~35℃ for more than 1 hour; open the bottle stopper, adjust the pH with acetic acid, shake well to allow the gas to escape completely, titrate with Na2S2O3 standard solution until light yellow, add starch indicator, and continue titrating until the blue color disappears, which is the end point. The volume of Na2S2O3 standard solution consumed is V2; Standard solution detection: Sodium phosphite pentahydrate was used to prepare the standard solution. According to its molar mass, 10g / L, 20g / L, and 30g / L phosphorous acid standard solutions were prepared respectively. The detection value was calculated by directly substituting the V2 value into the formula. The correction value was calculated by converting the sodium thiosulfate consumption value of the blank sample into the V2′ value and substituting it into the formula. Finally, the concentration of phosphorous acid was calculated by substituting it into the formula.

6. A method for detecting phosphorous acid according to claim 5, characterized in that, The concentration of phosphorous acid is calculated as follows: Where: C1—concentration of iodine standard solution, mol / L; Note: Equivalent to C(I2) = 0.05 mol / L; V1—the volume of the iodine standard solution used, mL; C2—concentration of sodium thiosulfate standard solution, mol / L; V2—the volume of sodium thiosulfate standard solution consumed by the test solution, mL; V0—the volume of sodium thiosulfate standard solution consumed in the blank, mL; V2′—the volume of sodium thiosulfate standard solution consumed by the test solution after correction, mL; V3—volume to be measured, mL; 82—Molecular weight of phosphorous acid.

7. A method for detecting phosphorous acid according to claim 6, characterized in that, The calculation formula of V2′ is:

8. A method for detecting phosphorous acid according to claim 5, characterized in that, The pH in the test sample and blank sample steps was adjusted to: pH < 4.

9. A method for detecting phosphorous acid according to claim 5, characterized in that, The purity of sodium phosphite pentahydrate is ≥98%.

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