Determination of Adipic Acid Content

Research on the Determination Method and Application of Adipic Acid Content
1. Experimental Background and Significance
Adipic acid, as an important industrial raw material, is widely used in nylon production, food acidity regulator, and pharmaceutical intermediate synthesis.
. Its content directly affects product quality parameters, such as polymer molecular weight distribution and food preservation effect. The content detection technology currently used in the industry needs to balance testing accuracy and operational convenience, so establishing standardized detection procedures is of great significance.
2. Analysis of conventional detection methods
① Classic acid-base titration method This method is based on the dicarboxylic acid properties of adipic acid and uses phenolphthalein as an indicator. Weigh 0.5g of the sample to be tested and dissolve it in 50mL of warm water. Ensure complete dissolution by ultrasonic oscillation. Use a 0.1mol/L sodium hydroxide standard solution for double endpoint titration. Record the first consumption when the solution pH reaches 8.3, and continue titration until pH 12.0 to determine the total reaction equivalent. Special attention should be paid to the influence of ambient temperature on the color development range of the indicator in the experiment. It is recommended to operate in a constant temperature room of 20-25 ℃. A rubber additive production enterprise once used this method for raw material acceptance, but due to individual differences in the judgment of double endpoints by operators, the RSD value between batches reached 3.2%. After configuring the automatic potentiometric titrator, the detection reproducibility was improved to within 1.5%. This indicates that the method selection needs to match the specific testing conditions of the enterprise.
② High performance liquid chromatography (HPLC) is a chromatographic analysis technique using a C18 reverse phase column, with column temperature controlled at 30 ℃, and a mobile phase of 0.05mol/L potassium dihydrogen phosphate solution (pH 2.5) - acetonitrile (95:5). Typical detection cases show that this method can increase the separation degree of adipic acid from similar substances such as succinic acid and glutaric acid to over 1.8, with a detection limit of 0.01 μ g/mL. A certain environmental monitoring station in Jiangsu Province applied this method to industrial wastewater monitoring and successfully detected the adipic acid pollutant discharged from a hidden pipe of a certain electroplating enterprise.
Page 1 of 2 3. Technical points and precautions
In the sample pretreatment process, the grinding fineness should be ensured to pass through an 80 mesh sieve. If the particle size is too large, it will cause incomplete dissolution. A third-party testing organization once caused a systematic 5% decrease in test values due to neglecting this detail.
Application of temperature compensation mechanism: When establishing the standard curve, seasonal temperature differences need to be considered, and a 0.15% correction coefficient for titrant concentration needs to be compensated in winter.
The instrument calibration procedure should include daily flow calibration at startup and weekly column efficiency testing, with calibration records kept for future reference.
4. Application example analysis
A food grade adipic acid production enterprise in Zhejiang has established a complete quality testing system during the ISO17025 certification process.
. The enterprise is equipped with a two person parallel detection mechanism: junior technicians use rapid titration method for online detection, and sample every two hours to ensure the stability of the production line; Senior engineers conduct monthly retesting of inventory raw materials using HPLC method, and validate the method in conjunction with standard substances. This grading detection strategy balances efficiency and accuracy, increasing the product qualification rate from 92% to 98.5%.
5. Conclusion and Suggestions: The acid-base titration method is suitable for the raw material acceptance process in small and medium-sized enterprises due to its simple equipment and low operating costs. The chromatographic analysis method is more suitable for high-end product development and quality arbitration scenarios. It is recommended that relevant enterprises regularly participate in inter laboratory comparisons, such as the T0884 proficiency testing project organized by CNAS, to continuously improve their testing capabilities. With the development of online Raman spectroscopy technology, real-time content monitoring in the production process is expected to be achieved in the future.