Method for detecting 1, 2-propylene glycol in high-absorptivity resin

Abstract

The invention discloses a method for detecting 1, 2-propylene glycol in high-absorptivity resin, which is characterized in that a sample is extracted through a methanol solution, water absorption swelling of sodium polyacrylate resin is effectively inhibited, and high-precision detection of trace 1, 2-propylene glycol is realized by combining sodium periodate oxidation and acetylacetone color development. The method has a recovery rate of more than or equal to 98% and a relative standard deviation of less than or equal to 2%, is significantly superior to a traditional water extraction method, and is suitable for industrial quality control of hygienic products, agricultural water-retaining agents and the like.

Description

Technical Field

[0001] This invention relates to the field of 1,2-propanediol detection technology, and specifically to a method for detecting 1,2-propanediol in highly absorbent resins. Background Technology

[0002] Sodium superabsorbent polymer (SAP) is widely used in hygiene products, agricultural water-retaining agents, and other fields. During its production process, 1,2-propanediol may remain in the final product. Due to the biotoxicity of 1,2-propanediol, its residual amount in related products needs to be strictly limited.

[0003] Currently, the main methods for detecting 1,2-propanediol include gas chromatography and high-performance liquid chromatography (HPLC). However, these methods suffer from problems such as expensive equipment, complex operation, and cumbersome pretreatment, making them difficult to widely apply in manufacturing enterprises. More importantly, sodium polyacrylate (SAP) rapidly swells into a gel upon contact with water (water absorption rate can reach over 300 g / g), and traditional extraction methods cannot effectively release the 1,2-propanediol encapsulated in the gel network, resulting in low extraction efficiency (typically <65%), which seriously affects the accuracy of detection.

[0004] In existing technologies, gas chromatography-based detection methods require complex derivatization processes, with single-sample detection times exceeding 3 hours and high equipment costs. While the traditional periodic acid oxidation-colorimetric method is lower in cost, it is only suitable for liquid samples, and its recovery rate is only 45-60% when directly used for SAP detection, which cannot meet the detection requirements.

[0005] Therefore, it is of great significance to develop a method for the detection of 1,2-propanediol that can effectively solve the gelation problem of SAP, improve extraction efficiency, and ensure detection accuracy. Summary of the Invention

[0006] To address the shortcomings of the prior art, this invention proposes a method for detecting 1,2-propanediol in highly absorbent resins, solving the problems of low extraction efficiency and poor detection accuracy in the prior art.

[0007] To achieve the above-mentioned technical effects, the present invention adopts the following solution: A method for detecting 1,2-propanediol in a highly absorbent resin, comprising the following steps: S1. Sample extraction: Mix the resin to be tested with methanol solution and extract using ultrasound. After extraction, centrifuge and collect the supernatant. S2, Oxidation reaction: Take the supernatant and add sodium periodate solution to adjust the pH to 4.0-5.0, and then carry out the reaction in the dark; S3. Colorimetric determination: Add sodium thiosulfate to quench residual oxidant, then add colorimetric reagent, heat in a water bath, and then cool to room temperature before measuring absorbance at 410-414 nm. Calculate 1,2-propanediol content based on formaldehyde standard curve.

[0008] In the preferred embodiment, the supernatant after extraction needs to be purified by a solid-phase extraction column, wherein the packing material of the solid-phase extraction column is C18 silica gel or PSA-graphitized carbon black composite packing material.

[0009] In a preferred embodiment, the solid-phase extraction column activation step is as follows: pretreatment with 5 mL of methanol and 5 mL of 65% methanol solution in sequence.

[0010] In a preferred embodiment, the concentration of the methanol solution is 60-70%, and the mass-to-volume ratio of the resin to be tested to the methanol solution is 1:15-20 (g / mL).

[0011] In the preferred embodiment, the ultrasonic extraction power is 200-300W, the temperature is 40-50℃, and the extraction time is 20-40min.

[0012] In the preferred technical solution, in step S2, dilute sulfuric acid is used to adjust the pH value.

[0013] In a preferred embodiment, in step S2, the sodium periodate solution contains a pH 4.5 acetic acid-sodium acetate buffer system, and the amount of acetic acid-sodium acetate buffer system added is 0.8-1.2 times the volume of the extract.

[0014] In a preferred embodiment, in step S2, the molar concentration of the sodium periodate solution is 0.05-0.1 mol / L.

[0015] In the preferred embodiment, in step S3, the color developing agent is acetylacetone-ammonium acetate containing 0.1-0.3% ascorbic acid, including: 25% ammonium acetate, 0.5% acetylacetone, 0.2% glacial acetic acid, and 0.1-0.3% ascorbic acid (w / v).

[0016] In the preferred embodiment, in step S3, the water bath heating temperature is 95-100℃ and the time is 10-20 minutes.

[0017] In the preferred technical solution, in step S3, the cooling method is ice bath cooling, and the temperature of the ice bath cooling is 0-4℃.

[0018] In the preferred embodiment, in step S1, the methanol aqueous solution contains 0.5% disodium EDTA.

[0019] Compared with existing technologies, the beneficial effects are: 1. High extraction efficiency: The methanol solution effectively inhibits the water absorption and swelling of SAP, resulting in an extraction rate of 1,2-propanediol of over 98.2%, which is much higher than the 65% of the traditional water extraction method.

[0020] 2. High detection sensitivity: The method detection limit can be as low as 0.005%, meeting industry testing requirements.

[0021] 3. Strong anti-interference ability: The addition of ascorbic acid effectively masks the interference of metal ions, and the solid phase extraction purification removes the interference of pigments and cross-linking agents.

[0022] 4. Low cost: The cost of single-sample testing is much lower than that of gas chromatography.

[0023] 5. Easy to operate: Short testing time, suitable for use by enterprise quality inspection departments. Attached Figure Description

[0024] Figure 1 This is a schematic flowchart of the detection method of the present invention. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0026] Example 1 1. Sample extraction Weigh 1.00 g of sodium polyacrylate (SAP) particles (0.1-0.5 mm in diameter) and add 20 mL of pre-cooled 65% methanol solution (containing 0.5% disodium EDTA). Sonicate at 50 °C for 30 min (250 W), centrifuge at 4000 rpm for 10 min, and collect the supernatant.

[0027] 2. Solid-phase extraction purification Activate the C18 column sequentially with 5 mL of methanol and then 5 mL of 65% methanol. Load 10 mL of the extract, discard the initial filtrate, and collect the subsequent 5 mL of filtrate.

[0028] 3. Oxidation reaction Take 5 mL of the filtrate, add 5 mL of 0.1 M sodium periodate solution (pH 4.5 acetate buffer), and shake in the dark for 35 min.

[0029] 4. Colorimetric determination Add 0.10 g of sodium thiosulfate and vortex to mix. Add 5 mL of colorimetric reagent (25% ammonium acetate + 0.5% acetylacetone + 0.1% ascorbic acid + 0.2% glacial acetic acid). Heat in a 100°C water bath for 15 min, then remove and cool to room temperature in an ice-water bath at 0°C. Make up to 25 mL with pure water. Using a blank reagent as a reference, measure the absorbance at 412 nm.

[0030] 5. Plotting the standard curve Plot a standard curve using formaldehyde standard solution: 1. Accuracy test Three concentration levels of 1,2-propanediol standards were added to SAP samples with known concentrations, and each level was measured in parallel six times. The recovery rate was calculated. The results are shown in Table 1. 2. Precision test The same SAP sample was measured 6 times consecutively, and the intra-day precision was calculated; the inter-day precision was calculated after 6 consecutive days of measurement. The results are shown in Table 2. 3. Specificity test Common interfering agents (triethyl citrate, polyethylene glycol 400) were added to SAP samples to investigate method specificity. The results are shown in Table 3. Comparison with reference method: The 1,2-propanediol content in 20 SAP samples was determined using both the method of this invention and gas chromatography-mass spectrometry (GC-MS), and the methods were compared. The results showed no significant difference between the two methods (P>0.05), with a correlation coefficient R²=0.998.

[0031] Comparative Example 1: Traditional water extraction method (demonstrating the ingenuity of solvent selection) Method: Weigh 1.00g of the same SAP sample as in Example 1, add 20mL of pure water to replace the 65% methanol solution in this invention, and extract under the same conditions (sonication at 50℃ for 30min). The subsequent oxidation, color development and determination steps are exactly the same as in Example 1 of this invention.

[0032] Extraction phenomenon: The sample swells rapidly upon contact with water, forming a non-flowing transparent gel. Even after ultrasonic treatment, it remains a solid gel and cannot be centrifuged to obtain a clear supernatant.

[0033] Test results: When the suspension was forcibly taken for reaction, the recovery rate was only 58.3%, and the RSD was 9.7%.

[0034] Conclusion: Traditional water extraction methods suffer from incomplete extraction and extremely poor reproducibility due to severe gelation problems, proving that using water alone as an extraction solvent is completely infeasible. This highlights the ingenuity of this invention in solving the technical problem by using a 60-70% methanol solution.

[0035] Comparative Example 2: Extraction with high-concentration organic solvents (demonstrating the non-obviousness of solvent ratios) Method: Weigh 1.00g of the same SAP sample and extract it using 90% methanol solution and 50% methanol solution respectively. The remaining steps are the same as in Example 1 of this invention. Conclusion: Neither excessively low (50%) nor excessively high (90%) methanol concentrations can simultaneously achieve the optimal balance between inhibiting swelling and efficient extraction. The present invention, through extensive experimentation, determined a specific range of 65% ± 2%, achieving unexpected technical effects and demonstrating its non-obviousness.

[0036] Comparative Example 3: Antioxidant omitted (demonstrating the necessity of the composite colorimetric agent formulation) Method: Weigh 1.00g of the same SAP sample, extract and oxidize it according to the method in Example 1 of this invention, and then perform a colorimetric reaction using a colorimetric reagent without adding 0.1% ascorbic acid. The remaining steps are exactly the same.

[0037] Color development: The reaction solution is dark yellow or light brown, rather than the characteristic bright yellow.

[0038] Detection results: The absorbance value measured at 412nm was significantly higher and unstable, with a calculated recovery rate as high as 125% and an RSD of 8.5%.

[0039] Conclusion: Trace amounts of metal ions (such as Fe) in SAP ³⁺ Cu ²⁺ Interfering ions can interfere with the colorimetric reaction, leading to significant deviations in results. This invention introduces a specific proportion (0.1%) of ascorbic acid into the colorimetric reagent, effectively masking interfering ions and ensuring the accuracy and stability of the detection. This technical feature is indispensable.

[0040] Comparative Example 4: The solid-phase extraction purification step was omitted (demonstrating the importance of the purification process). Method: Weigh 1.00g of SAP sample containing common additive (triethyl citrate), extract it according to the method of Example 1 of this invention, omit the solid phase extraction purification step, and directly take the supernatant for oxidation and color development.

[0041] Color development: The reaction solution is cloudy with slight suspended matter.

[0042] Test results: The recovery rate was 112.3%, and the RSD was 7.2%.

[0043] Conclusion: Impurities such as pigments and cross-linking agents in the resin can interfere with the colorimetric reaction, leading to false positive results and decreased precision. The C18 solid-phase extraction purification step introduced in this invention can specifically remove lipid-soluble interfering substances, which is key to ensuring the specificity and reliability of the method.

[0044] In summary, the present invention has the following advantages: 1. High extraction efficiency: The 60-70% methanol solution effectively inhibits the water absorption and swelling of SAP, resulting in an extraction rate of 1,2-propanediol of over 98.2%, which is much higher than the 65% of the traditional water extraction method.

[0045] 2. High detection sensitivity: The method detection limit can be as low as 0.005%, meeting industry testing requirements.

[0046] 3. Strong anti-interference ability: The addition of ascorbic acid effectively masks the interference of metal ions, and the solid phase extraction purification removes the interference of pigments and cross-linking agents.

[0047] 4. Low cost: The cost of a single sample test is only 18 yuan, which is far lower than the 150 yuan of gas chromatography.

[0048] 5. Easy to operate: The testing time is only 1.5 hours, making it suitable for use by enterprise quality inspection departments.

[0049] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

Claims

1. A method for detecting 1,2-propanediol in a highly absorbent resin, characterized in that, Includes the following steps: S1. Sample extraction: Mix the resin to be tested with methanol solution and extract using ultrasound. After extraction, centrifuge and collect the supernatant. S2, Oxidation reaction: Take the supernatant and add sodium periodate solution to adjust the pH to 4.0-5.0, and then carry out the reaction in the dark; S3. Colorimetric determination: Add sodium thiosulfate to quench residual oxidant, then add colorimetric reagent, heat in a water bath, and then cool to room temperature before measuring absorbance at 410-414 nm. Calculate 1,2-propanediol content based on formaldehyde standard curve.

2. The method for detecting 1,2-propanediol in a highly absorbent resin as described in claim 1, characterized in that, The supernatant after extraction needs to be purified by a solid-phase extraction column, the packing of which is C18 silica gel or PSA-graphitized carbon black composite packing.

3. The method for detecting 1,2-propanediol in a highly absorbent resin as described in claim 2, characterized in that, The solid-phase extraction column activation step is as follows: pretreatment with 5 mL of methanol and 5 mL of 65% methanol solution in sequence.

4. The method for detecting 1,2-propanediol in a highly absorbent resin as described in claim 1, characterized in that, The concentration of the methanol solution is 60-70%, and the mass-to-volume ratio of the resin to be tested to the methanol solution is 1:15-20 (g / mL).

5. The method for detecting 1,2-propanediol in a highly absorbent resin as described in claim 1, characterized in that, The ultrasonic extraction power is 200-300W, the temperature is 40-50℃, and the extraction time is 20-40min.

6. The method for detecting 1,2-propanediol in a highly absorbent resin as described in claim 1, characterized in that, In step S2, dilute sulfuric acid is used to adjust the pH value.

7. The method for detecting 1,2-propanediol in a highly absorbent resin as described in claim 1, characterized in that, In step S2, the sodium periodate solution contains a pH 4.5 acetic acid-sodium acetate buffer system, and the amount of acetic acid-sodium acetate buffer system added is 0.8-1.2 times the volume of the extract.

8. The method for detecting 1,2-propanediol in a highly absorbent resin as described in claim 1, characterized in that, In step S3, the colorimetric agent is acetylacetone-ammonium acetate containing ascorbic acid, comprising: 25% ammonium acetate, 0.5% acetylacetone, 0.2% glacial acetic acid, and 0.1-0.3% ascorbic acid (w / v).

9. The method for detecting 1,2-propanediol in a highly absorbent resin as described in claim 1, characterized in that, In step S3, the water bath heating temperature is 95-100℃ and the time is 10-20 minutes.

10. The method for detecting 1,2-propanediol in a highly absorbent resin as described in claim 1, characterized in that, In step S1, the methanol aqueous solution contains 0.5% disodium EDTA.

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