Abstract: 1D proton nuclear magnetic resonance (NMR) spectroscopy is a high-resolution, non-invasive technique widely used for structure elucidation and composition analysis. However, its application to complex systems is often limited by overlapping peaks from similar chemical shifts and J-coupling, along with concentration variations obscuring weak signals from low-abundance compounds. To address this, we propose Hadamard-DQF-LMO, integrating longitudinal multi-spin orders (LMOs), Hadamard encoding, and double quantum filtering (DQF). The method employs DQF to selectively detect LMO signals while suppressing strong interference. The incorporation of polychromatic transition pulses and Hadamard-encoded 180° pulses enables parallel acquisition of multiple frequency, enhancing sensitivity. Tests on orange juice and mixed amino acid samples demonstrate peak separation with improved selectivity and SNR, offering a robust approach for complex-system NMR analysis.

Key words: MRS, Hadamard encoding, longitudinal multi-spin orders, double quantum coherence