Sample&Rotor

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 HRMAS Sample and Rotors

The rotors most commonly used for MAS are made of zirconium oxide (Zirconia). Rotors can be either filled entirely with sample or they can be used with rotor inserts. Inserts are provided to improve shimming and RF in homogeneity, and are useful when the amount of sample is limited. The maximum spinning rate for 4 mm Zirconia rotors is about 15 kHz, but is limited to lower speeds when using the spacers. A full rotor has a sample volume of about 80 ul; with a spherical insert the volume is reduced to about 25 ul. Numbered rotors are available to easily distinguish between different samples. The function of the rotor cap is twofold: firstly, to close the rotors, and secondly, to provide the driving of the rotor. There are several types of caps available. The standard caps are made of Kel-F, which can be used in a temperature range from 10C to +50C. This material will shrink at lower temperatures and soften at more elevated temperatures. However, for a more extended VT  range (-30C to +70C) caps made from macor or boron nitride can be used. Those materials have temperature coefficients similar to Zirconia. Figure below. Zirconia rotor with Kel-F cap, upper spacer, cylinder head screw, and sealing grub screw to provide a spherical sample volume.

 

Cap Removal:

Use Liquid N2. See pictures

Spinning the Rotor using a test station before insert the sample to the probe.

To Purchase Rotors call:

Parts number,????

 

How to Load Your HRMAS  Samples

In order for the rotor to spin stable and fast, the rotor has to be well balanced. Load the sample loosely into the rotor barrel and tap the rotor lightly on a hard surface. Do not attempt to pack the material tightly into the spinner. If you wish to add more sample into the rotor, it is better to spin up the rotor first, so that the sample is packed against the walls of the barrel, and then add additional material. Liquid or viscous samples are easily loaded using a syringe or a small pipette. Solvent swelling can be done with the powdered sample in the rotor. Push the rotor cap on all the way; if the cap is improperly positioned the rotor may not spin. Clean the outside of the rotor with a tissue, so that no sample ends up in the MAS stator. Mark half of the beveled rim on the bottom of the rotor with a black marker for optical spin rate detection.

Important Note: The rotor bore and the spacer must be absolutely clean. The lower spacer will be destroyed if it is removed after being inserted into the bore. If you want to know detailed procedure of loading special HRMAS sample, please contact Dr. Shaoxiong Wu.

 

 

Photo by Shaoxiong Wu, Lake Taheo, CA,  October,  2003

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Last updated: 02/15/04.