Heteronuclear Double Quantum Filters

Double quantum filters are used to filter out single quantum magnetization and allow the passage of double quantum magnetization. In the proton observe heteronuclear case, the double quantum filter (like the BIRD filter) allows the selective observation of the weak satellite signals from protons coupled to dilute spin I = 1/2 X nuclei (e.g. X = ¹³C, ¹⁵N, ²⁹Si ....) but rejects the strong singlets from the uncoupled protons in the vicinity of ¹²C, self decoupled ¹⁴N, and ²⁸Si . The figure below illustrates the heteronuclear double quantum filter described by Stefan Berger and Siegmar Braun in 200 and More NMR Experiments applied to the ¹H NMR spectrum of tetramethylsilane. The bottom trace of the figure shows a conventional ¹H NMR spectrum. The middle trace was collected using a ¹H-²⁹Si double quantum filter and shows only the ¹H-²⁹Si doublet. The top trace was collected using a ¹H-¹³C double quantum filter and show only the ¹H-¹³C doublet. In both cases there is excellent suppression of the ¹H singlet signal.