Ultrafast 2D COSY with constant-time phase-modulated spatial encoding

Recently ultrafast techniques enable 2D NMR spectra to be obtained in a single scan. They have been successfully applied for 2D COSY, TOCSY, DOSY, HMQC, and J-resolved spectra. In this paper, two alternative ultrafast 2D COSY methods (g-COSY and gDQF-COSY) based on continuous constant-time phase-modulated spatial encoding were proposed. Theoretical expressions of the resulting signals were deduced. Experiments were performed to verify our theoretical analysis and the feasibility of the methods. Comparisons between the experimental results of our methods and those of the previous real-time phase-modulated spatial encoding method demonstrate that the signal-to-noise ratio and resolution of the 2D COSY spectra are improved, and a good 2D COSY spectrum is easier to achieve by using our methods.