COSY block

COSY (Correlated SpectroscopY)is a simple mixing process to transfer polarisation between J-coupled homonuclear spins.

A single ^π/₂ (or 90°) pulse is used to transfer antiphase magnetisation from one nucleus to a second nucleus to which it is coupled. If we have a system with two nuclei I₁ and I₂ that are j-coupled and prior to the pulse we have antiphase magnetisation of I₁ with respect to I² (2I_1YI_2Z). After the pulse we have antiphase magnetisation of the I₂ nucleus with respect to I₁ (-2I_1ZI_2Y).