Diagonal free processing of conventional phase sensitive COSY using Filter Diagonalization Method

Diagonal peak suppression of homonuclear multi-dimensional correlation NMR spectra is an area of research that has seen a constant influx of new methods designed to remove the intense but mostly redundant diagonal auto-correlation peaks. These methods, while at their job, aim to retain the intensity, position, lineshape, and sensitivity of the information-rich cross peaks as faithfully as possible. Most of these methods offer some alternative data acquisition scheme that delivers the same correlation information as the original spectrum but with suppressed diagonal peaks. Here we present not an alternative pulse sequence, but a new processing tool based on the Filter Diagonalization Method (FDM) which produces a diagonal free phase-sensitive COSY spectrum from the conventionally acquired data. The method revisits difference spectroscopy but with an unconventional pair of one experimental and one FDM generated synthetic spectrum instead of two experimental ones and thus is economical in terms of spectrometer time. To demonstrate, the processing tool was applied first on a simple coupled two-spin system of 2-Bromo-5-chlorothiophene and then to a more complex system of several coupled spins in sucrose.