Pulsed Field Gradient (PFG) Modules
A Pulsed Field Gradient (PFG) module applies a gradient
in B0 at programmed parts of the pulse sequence.
The gradient system produces an intense gradient
and then returns to spectroscopic conditions quickly.
This gradient can perform several functions, including shimming,
solvent suppression, coherence pathway selection and diffusion measurements
(DOSY).
The Performa family of PFG modules provides unsurpassed performance in gradient
experiments for high resolution liquids applications -
the relevant parameters are the gradient strength
and stability, the duty cycle of the gradient system, and
the time to recover to spectroscopic conditions.
When used with Varian's high-performance PFG probes,
the Performa PFG modules provide the following, even under the most
demanding experimental conditions:
- Rapid recovery and minimal signal distortion
- Low noise
- True constant current
- Linear gradient amplifiers have no turning on or blanking
- High-precision gradient waveform control
Both VNMRS and 400-MR consoles are equipped by standard with 30 MB of gradient waveform memory for gradient shaping.
Performa I
The Performa I gradient system produces pulses with strengths of up to
20 Gauss/cm. This module is the basic gradient system, perfectly suitable for the use with gradient experiments
like gCOSY and gHSQC,
gradient shimming and basic diffusion (DOSY) experiments involving mixtures of small molecules.
Performa IV
The Performa IV module applies gradients with strengths of up to
65 Gauss/cm. This module is the best choice for more demanding tasks like gradient water suppression,
and more advanced diffusion (DOSY) experiments on mixtures of bigger molecules.
Performa XYZ
The Performa XYZ module applies gradients in B0 along
three distinct axes.
These gradients can perform several functions, including solvent
suppression and coherence pathway selection. The gradient system
produces gradient pulses with strengths of up to 25 Gauss/cm on
X and Y, and up to 65 Gauss/cm on Z. The relevant parameters now include the gradient axis and
gradient strength.
PFG Profile and Recovery
Profile of RF sensitivity window using 1% doped
D2O sample
Typical gradient recovery profile. The plateau region starts at approx. 50 μs indicating the fast
gradient recovery of a modern PFG probe with shielded gradient coil.
|
