The 2D Zero-Quantum (ZQ) experiment is an example of multiple-quantum Spectroscopy. It offers a homonuclear chemical shift correlation 2D map, alternatively to COSY-type experiments. ZQC are insensitive to magnetic field inhomogeneity and, for this reason, ZQ experiments are very interesting for in-vivo studies and for applications using pulsed field gradients.

Easy implementation on any AVANCE spectrometer.

The basic ZQ experiment can be obtained by replacing the first 90º 1H pulse of the basic two-pulse COSY sequence by a multiple-quantum preparation period (90º-delay-45º or 90º-delay-135º cluster) ( 84JMR326-59 and 88JMR241-76 ). In order to avoids undesirable chemical shift evolution, an spin-echo is used. Modified ZQ experiments have been proposed as, for instance, a refocused ZQ ( 86JCS44 ), a refocused CT-ZQ ( 86JMR391-69 ), the so-called SUCZESS ( 85JMR151-64 ), the refocused SUCZESS ( 86JMR585-69 and 87JMR171-74 ) and the APSZQC ( 91JMR195-93 , 91JMR191-94 and 93JMRA193-105 ) experiments.

The 2D ZQ experiment can be recorded in routine/automation modes. The most important parameter to consider is the delay of the MQ period which is optimized to 1/2JHH in order to obtain anti-phase coherence. The spectral width in F1 must be twice the largest possible ZQ or difference frequency. P- and N-type signals can not be separated and therefore a magnitude-mode presentation is most useful. However, phase-sensitive absorption-mode ZQ spectra can be obtained using the APSZQC experiment.

Tutorials: 2D homonuclear experiments

Tutorials: 2D gradient-based homonuclear experiments

The 2D matrix contains a series of correlation multiplets centered at the SQ chemical shift in F2 (as in COSY) and at the ZQ frequencies (differences of chemical shifts between coupled spins) in F1. ZQ spectra often contain intense autocorrelation (F1 zero-frequency) peaks which can be efficiently removed usind the APSZQC experiment. Some examples can be found in 88MRC839 , 88MRC980 and 92MRC779 .

Related experiments:

2D homonuclear experiments

2D gradient-based homonuclear experiments