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| Parameter | Status | Consequence |
| Sample Spinning | on | Narrower lines; 10 mm or 20 mm samples may require Teflon vortex plugs. |
| off | Best phase stability: do not spin for 2D, 3D experiments or difference spectra. | |
| Temperature Regulation | on | Required for long-term experiments or when maximum resolution is required; 5-10 minutes equilibration time required, even for regulation near ambient temperature. |
| off | Not needed for quick, routine spectra at ambient temperature. | |
| Probe Tuning | required | When changing observe nucleus; for optimum sensitivity and shortest pulse lengths; to minimize RF-heating when using broad-band decoupling; standard for multi-pulse 2D/3D/4D experiments |
| not required | For routine 1-D use when pulse widths do not need to be carefully calibrated: assumes that the probe was properly tuned. Note that radical changes in solvent composition e.g. CDCl3 vs. high-salt aqueous will significantly alter the frequency tuning and impedence matching characteristics of the tuned circuit. | |
| Deuterium Lock | on | Provides compensation for magnetic field drift: required for highest resolution work; the amplitude of the lock feedback signal ("lock %") is used for shimming. |
| off | Deuterium observe; deuterated solvent not available; shimming is accomplished using a separate deuterated standard with the same geometry (liquid height/tube size) as the sample to be analyzed; alternately the shims may be adjusted while observing the shape of the observe nucleus FID. | |
| Shimming | . | Brief adjustments of axial shims (z1, z2, and maybe z3) are required for routine work; for highest resolution, extensive adjustment of all shims may be required for solid-state work room-temperature shims might not be used at all. Odd-order shims (e.g. z1, z3, z5) have symmetrical effects on line shape; even-order shims (e.g. z2, z4) have asymmetical effects on line shape. |
| Gain Adjustment | . | Amplification of "audio" signal output of the RF detector; required to match signal strength to digitizer (ADC) voltage measurement range: if the signal overflows the ADC it will be "clipped", resulting in a distorted spectrum. If the gain is too low, weak signals may fall below the measurement threshold of the ADC. |
| auto-gain | VNMR: gain='n' insures that a suitable gain is used, but requires extra time when each data acquisition is started. May confuse automated series of experiments, as with arrayed variables | |
| manual gain | VNMR: gain=1 to 60 | |
| Pulse Width Calibration | "pw" | Required when exact length of "90-degree" or "180-degree" pulses needs to be known. This is always done when a new probe is installed and typically repeated prior to experiments that require careful calibration, e.g. relaxation measurements, 2D, 3D, multiple quantum filters, etc. In the long term, the 90-degree pulse width may be a quality control indicator of probe health & performance. |
| Relaxation Delay | "d1" | The pulse-repetition time tr = (d1+at) must be long enough to allow adequate (T1) relaxation between repeated scans. For spectra where quantitative intensity information is required one should use tr > 5<·>T1 |
| Acquisition Time | "at" | Length of time (seconds) during which the NMR signal is sampled and digitized. "at" must be sufficiently long to allow the FID to decay and avoid truncation artifacts to ensure full spectral resolution. |
| Spectral Width | "sw" | The spectral observation window. Must be wide enough to encompass all resonances. Resonances outside the spectral window may be "folded-in" (aliased). Excessive width will result in excessive noise. The spectral width is the reciprocal of the dwell time (digital sampling interval). |
| Number of Data Points | "np" | The real+imaginary data table size: the product of the dwell time and the acquisition time collected in two channels. Each data point requires 4 bytes of data storage |
| Transmitter Offset | "tof" | An offset in Hz combined with the standard transmitter frequency for each nucleus that determines the center frequency of the quadruture-detected spectrum |