The ge-1D Multiple-Quantum (MQ) experiment permits to obtain 1D spectra in which only protons belonging to an specific spin system has been selected or suppressed by means of PFGs.

Easy implementation on AVANCE spectrometers equipped with pulsed field gradients.

The ge-1D MQ pulse sequence consists of the following steps:

• A multiple-quantum block (90º-delay-180º-delay-90º) to create MQCs.
• A fixed period in which a PFG is usually inserted to dephase all magnetization.
• A 90º pulse to creates antiphase SQC. A refocusing gradient is applied just before this pulse or into an optional refocusing period incorporated to achieve in-phase magnetization.
• Proton acquisition as usual.

The ge-1D Double-Quantum (DQ) experiment uses a 1:2 gradient ratio to select DQCs during the fixed period. On the other hand, in a ge-1D Zero-Quantum (ZQ) experiment, a single dephasing PFG is applied during the fixed period in order to select ZQCs. In this case, the refocusing gradient is omitted.

Some applications have been reported:
 

• Double-Quantum filtering method to detect lactate ( 88JMR355 ), citrate ( 94JMRB58-105 ), GABA ( 93JMRB165-101 and 95JMRB169-109 ) and ethanolamine ( 96JMRB97-111 ) resonances in In Vivo Spectroscopy.
• Selection of ZQCs ( 93JMRA111-104 , 95JMRA235-113 , and 96JMRA113-118 ).
• An excellent review on the use of NMR methods to detect in-vivo metabolites can be found in 97NMRB435 .

The ge-1D MQ experiment can be run with minor changes from a predefined parameter set. The interpulse delay in the MQ block is optimized to 1/(2*J_HH).

In 1D MQ spectra affords a 1D 1H spectrum in which only protons of selected spin systems are observed. Thus, in a ge-1D DQ spectrum, singlets are efficiently removed.

Also see 2D ZQ, 2D DQ and ge-2D multiple-Quantum experiments.