pulsed gradient spin echo
Definition and meaning of pulsed gradient spin echo in chemistry.
A pulsed gradient spin echo is an advanced nuclear magnetic resonance technique used to measure the translational diffusion of molecules in a liquid or gas. It involves applying precise magnetic field gradients in short pulses during a standard spin echo sequence to encode and decode the spatial positions of nuclear spins.
In more detail
This analytical method is highly sensitive to the random Brownian motion of molecules, allowing chemists to determine diffusion coefficients with high accuracy and minimal disturbance. The first gradient pulse spatially encodes the phase of the nuclear spins across the sample, while the second gradient pulse, applied after a 180-degree radiofrequency pulse, reverses this spatial encoding. If the molecules have moved due to diffusion during the time interval between the gradient pulses, the refocusing is incomplete, which results in measurable signal attenuation. The degree of this signal loss provides a direct measure of the diffusion coefficient for the species.
Key facts
| Field | Physical Chemistry |
|---|---|
| Measured Property | Translational diffusion coefficient of molecules |
| Key Component | Application of precise magnetic field gradients |
Pulsed gradient spin echo nuclear magnetic resonance is frequently used in physical chemistry to study the size and shape of polymers or micelles in solution by measuring their precise diffusion rates.
Frequently asked questions
What specifically causes the signal attenuation in this analytical technique?
Signal attenuation is directly caused by the random diffusion of molecules, which inherently prevents the perfect refocusing of the nuclear spins by the second gradient pulse.