Development of RP-HPLC–UV Technique for “N,N’-Disubstituted Terephthalamides”, the Depolymerized End Products of Polyethylene Terephthalate Waste

Amides often exhibit poor solubility in common solvents, posing challenges to their efficient separation. However, the development of robust RP-HPLC methods becomes essential to overcome this limitation, enabling accurate and reliable separation, quantification and characterization of these compounds. An RP-HPLC–UV technique has been developed for evaluating N,N’-dibutylterephthalamide, N,N’-dimethylterephthalamide, N,N’-bis(2-hydroxyethyl)terephthalamide and terephthalic dihydrazide obtained through aminolytic depolymerization of polyethylene terephthalate waste. The data obtained has been analyzed to arrive at most appropriate values of essential parameters to obtain highly resolved HPLC chromatograms using odyssil C₁₈ column (4.6 × 250 mm, 5 μm) from Agela Technologies with a UV detector. Dimethyl formamide and dimethyl sulfoxide emerged as the most suitable mobile phases with an isocratic run of 10 min at a flow rate of 0.4 mL/minute. Effect of temperature and concentration on HPLC chromatograms was also investigated for N,N’-dibutylterephthalamide from 30 to 50 ℃ and 0.5 mg to 2.5 mg/10 mL of solvent, respectively. 1–2.5 mg/10 mL concentration was found to be most suitable with the column temperature of 40 ℃. Method validation consisted of linearity, intra- and inter-day precision, detection and quantitation limit. The validation experiments confirmed the precision of the present method, with RSD% and CV% values for both intra- and inter-day precision measuring below 1.9% and 0.5%, respectively. The method was linear in the range of 0.5–2.5 mg/10 mL solvent (R² = 0.98). Detection and quantitation limit were determined to be 1.32 and 4.02 mg/10 mL, respectively, for peak 1 and 0.90 and 2.75 mg/10 mL, respectively, for peak 2.