Inserting NMR Sample
Adjusting sample depth with a sample gauge
The optimal volume for NMR samples is 500-600 uL for 5 mm regular NMR tubes and ~300 uL for 5 mm Shigemi tubes. Before the tube is put into the magnet, the optimal position of the tube in the sample holder should be measured in the gauge as shown in the figure below.
First, the NMR tube has to be inserted into a spinner turbine. For best results, NMR tubes should be positioned in the spinner turbine so that the sample volume will be centered in the NMR probe. This should be done with the help of a sample gauge, which usually has a center line and rectangular markings to indicate the probe geometry.
A sample gauge also has an adjustable bottom, which is typically fixed at a proper level by your NMR facility manager. Never position a tube lower than the bottom of the gauge! Setting a sample tube too low may cause it to break, as well as contaminate and damage the probe!
It is also important to make sure that the tube sits firmly in the spinner. If your sample slides too easily inside a spinned, that may indicate that its rubber o-rings need replacement.
Figure1. Positions of NMR tube in the gauge. Left, regular tube; right, shigemi tube.
Inserting and ejecting
In VNMR:
- Click on the Acqi button or type acqi
- Use the Insert and Eject buttons in the Acqi window
In VNMRJ:
- Click on the Setup tab
- Uset the Insert sample and Eject sample buttons in the middle of the screen
You can also type insert or i and eject or e at the VNMR or VNMRJ prompt.
Procedure
- Eject the current sample first. Even if there is no sample in the magnet you need to use eject to create the airflow.
- Remove the ejected sample.
- Verify that you have the airflow to support your sample. Carefully insert the sample in the bore.
- Select insert to lower your sample
Figure2. Acquisition window.
Do not leave the spectrometer with an open bore for long periods of time. If you have to remove a sample and have nothing else to measure, either insert a standard NMR sample or cover the bore with a dedicated plug.
-- Main.GaohuaLiu - 24 Jan 2007