Probe Qs: One parameter affecting sensitivity is the probe Q. Q is defined as the frequency of the resonant circuit divided by the the half power bandwidth. Many of today's probe have unloaded Qs greater than 300. If all the other parameters are the same, the higher the probe Q, the greater the sensitivity.

The Sample: One component which lmits probe Q is the sample. The sample increases loss in the resonant circuit by inducing eddy current in the solvent. The more conductive the samplethe more the losses and the lower the probe Q. This is often seen by the longer 90 degree pulses with water samples than with organic sovent samples.

The losses in the sample are induced by the electric field values inside the probe. The more distributed capacitance a probe has in its resonant circuit, the lower the electric field values. Therefore a probe with distributed capacitance is less affected by the sample. Unfortunately the capacitor usually has ahigh resistance than the coil. Therefore the use of distributed capacitors lowers the probe's unloaded Qs, but can raise the loaded Qs. This statement reduces to the probe designer's need to compromise probe design between organic and water samples.
_______From Acorn NMR Inc.

Shimming Problems:
A good shimming can be done in minutes, but also could take several hours or even days. An understanding of the shimming interactions and their effect on the NMR signal will make the shimming easier.
_______From Shaoxiong Wu

You treat NMR instrument well, it will serve you better. You know more about NMR, you will be more productive.

Spinning Shimming:
If the sample has a fairly good shimming, but the linewidth is not good enough to provide good resolution, do following steps:
1. Spin sample at rate 15-20 hz. Adjust Z1 and Z2 to maximize the lock signal.
2. Adjust Z3 clockwise to decrease the signal intensity by 20%, then adjust Z1 and Z2 to maximize the lock signal. Compare with the initial intensity. If it is better, adjust Z3 more in the same direction, then adjust Z1 and Z2 until reach to maximum. If it is worse, adjust Z3 anticlockwise to decrease signal intensity by 20%, then adjust Z1 and Z2.
3. Adjust Z4 in the same fashion as stated in step 3. It may take much longer since after Z4 is changed, steps 1 and 2 must be followed.
4. Adjust Z5. The best way is the same as above.

A good shimming is the most important feature for the performance of an NMR spectrometer. The lineshape measurement: Use a 1% CHCl3 in CDCl3 standard sample. Measure the linewidth at 50%, 0.55% and 0.11% of the peak height. good NMR peak should be a Lorentzian line line shape.

50%: < 0.3Hz
0.55%: <13.5x0.3=4.05Hz
0.11%: <30x0.3=9.00Hz

Compaq is considering changing the command "Press Any Key" to "Press Return Key" because of the flood of calls asking where the "Any" key is.

True story from a Novell NetWire SysOp.
Caller: "Hello, is this Tech Supporter?
Tech: "Yes, it is. How may I help you?
Caller:"The cup holder on my PC is broken and I am within my warrenty period. How do I go about getting that fixed?
Tech: "I'm sorry, but did you say a cup holder"?
Caller: "Yes, it's attached to the front of my computer."
Tech: "Please excuse me if I seem a bit stumped, it's because I am. Did you receive this as part of a promotional, at a tradeshow? How did you get this cup holder? Does it have any trademark on it?"
Caller: "It came with my computer, I don't know anything about promotional. It just has '4X' on it."
At this point, the Tech Rep had to mute the caller, because he couldn't stand it. The caller had been using the load drawer of the CD-ROM drive as a cup holder, and had snapped it off the drive!

The NMR Center has received several complaints about their boss's lastname.
After the new INOVA400 was installed, each research group has one or two NMR user IDs to logon to the computer. According to our department tradition, the last names of the supervisors are used to setup the accounts. Dr. Liebeskind's students have to type tencharacters to login and take 6 seconds more on the instrument while Dr. Hill's students only have four. Should Dr. Liebeskind pay for that 6 seconds NMT usage fee, just because he has a longer lastname?