Triple-quantum filter

The selectivity of multi-quantum filters is demonstrated in Fig. 7.2.28 by spectra recorded for poly(isoprene) (PI) with the multi-quantum filter from Fig. 7.2.26(d) [Schl 1, Schl2, Schl3]. The conventional single-quantum H NMR spectrum of PI shows a broad line with little to no chemical-shift resolution. But the double- and triple-quantum filtered spectrum of the material exhibit peaks at different chemical shifts which can be assigned primarily to the signals from CH2 and CH3 groups, respectively. At longer... 

We now apply the above theory to modelling of the pulse-and-collect , Hahn spin-echo and triple-quantum filtered T2 experiments. 

Fig. 2. (A) 87Rb triple-quantum filtered NMR spectrum of 2g% agarose in RbCl. (B) Dependence of the triple-quantum signal amplitude on the triple-quantum creation time—a biexponential fit to the peak heights of the series of spectra yields the and T2f relaxation times. From Ref. 51, with permission.

Fig. 9. Single- and triple-quantum filtered 87 Rb spectra as a function of BSA concentration. The triple-quantum creation time was set to rmax for each sample. The triplequantum filtered spectrum (10240 scans) is plotted above the corresponding singlequantum spectrum (64 scans). The downfield peak in the single-quantum spectrum is a Rb and KI reference. From Ref. 72, with permission.

E9-7. The CTP and pulse sequence of triple-quantum filtered COSY are... 

Devise a gradient selected version of the triple-quantum filtered COSY experiment, whose basic pulse sequence and CTP was given in E9-7. Your sequence should include recommendations for the relative size of the gradients used. The resulting spectrum must have pure phase (i.e. p = 1 must be preserved in /,) and phase errors due to the evolution of offsets during the gradients must be removed. 

When applied to longitudinal magnetization, the C7 sequence in general excites even-order multiple (double)-quantiun coherences. Applying C7 to transverse magnetization, in general leads to excitation of odd-order multiple-quantum coherences. Using POST-C7, triple-quantum coherence in fully C-labelled L-alanine has been excited in this way, with a triple-quantum filter efficiency of 8% for the central and 4% for the two peripheral spins. ... 

Refinements of the technique can be used which eliminate all resonances from one- and two-spin systems, i.e., singlets and doublets (triple-quantum filtered COSY), and so on for higher-spin systems. The DQF-COSY experiment is not as sensitive as the normal COSY approach and the higher quantum filtering is usually achieved using pulse phase cycling with increments in phase angles of less than 90°, a facility not always available on older spectrometers. 

Zinc. Transverse triple-quantum filtered NMR spectroscopy of in water has been used to study the properties of water in insulin solutions at different concentrations and pH values. " ... 

Incorporation of a triple-quantum filter produces a spectrum with signals due only to three or more coupled spins with two resolvable couplings. There are no singlets or doublets, including anomeric resonances, although suppression is not absolute, due to the presence of small couplings along four or more bonds. 

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