Thursday, April 21, 2011
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.