Quantitative 2D HSQC with Non-Uniform Sampling for the Determination of Paracetamol in Compound Preparations

Paracetamol (APAP) is a common active ingredient of compound cold preparations, and its routine one-dimensional 1H-NMR quantification is compromised by overlap with the aromatic signals of co-formulated caffeine and chlorpheniramine. A rapid method based on two-dimensional 1H−13C HSQC combined with non-uniform sampling (NUS) was established: with DMSO-d6 as the extraction solvent and 1,4-dinitrobenzene (δH = 8.45 ppm) as internal standard, the cross-peaks at δH/δC = 7.33/121.26 and 6.67/115.44 ppm serve as two independent quantitative channels, requiring neither chromatographic separation nor an analyte-matched reference standard. Under the optimised conditions the acquisition time per sample was 26′35″, one quarter of that of uniformly sampled HSQC (108′25″). The method was linear over 0.625–40.0 g•L−1 (R2 = 0.9999) with LOD 0.397 g•L−1 and LOQ 1.20 g•L−1; precision was 0.5 %–0.74 % RSD, 48 h stability 0.83 % RSD, and recovery 98.15 %–99.89 %. The results for ten commercial preparations (capsules, tablets and a granule) deviated from the pharmacopoeial HPLC method by less than 4 % — Bland–Altman bias +0.93 % with 95 % limits of agreement of −2.1 % to +3.9 % and no significant systematic bias (paired t-test, p = 0.09) — and from the label claims by less than ±2 %; the lowest content verified experimentally was 1.2 % w/w, and lower contents were not examined and should not be extrapolated. The method is simple to operate, determines APAP in compound preparations rapidly and accurately, and provides a reference for the quality control of manufacturers and regulatory authorities.