Figure 2.

Experimental demonstration of SPASM’s ability to measure indirect-domain evolution frequencies, illustrated for a model Chloroform case whose ¹³C offset was systematically shifted over 2 kHz in 100 Hz steps for a fixed indirect evolution delay Δt₁ = 1 ms. (A) Post-acquisition processing involves separating the experimental data into alternating points corresponding to N (echo) and P (anti-echo) FIDs. Once individually Fourier transformed and phased to yield purely-absorptive 1D spectra, each peak leads to the phase parameters ϕ_N,i and ϕ_P,i from which the indirect frequency can be determined (eq. 2). (B) Phase difference exhibited by CHCl₃’s sole ¹H resonance when acted upon by the SP-SWAT sequence as a function of an artificially-varying indirect frequency offset F₁. Green data points illustrate the periodic phase wrapping arising from the limits on a measurable phase difference Δϕ = ϕ_N-ϕ_p; phase-unwrapping yields the blue points, in excellent fit with the prediction of eq. 3.