NMR High Pressure Probes, Samples, and other details

High Presssure probe
Berylium Copper Pressure Chamber, expanded view

ZIRCONIUM OXIDE NMR SAMPLE TUBES

	8mm high pressure NMR sample tube
	5mm high pressure NMR sample tube

"SAFETY ISSUES OF HIGH PRESSURE NMR"

"THE MAIN POINT TO BE EMPHASIZED IS TO FIND ASSISTANCE FROM A PERSON WHO IS HIGHLY EXPERIENCED IN THE PROBLEMS OF SAFETY AT HIGH PRESSURE".

There are three main hazards to personnel (and equipment) doing high pressure NMR work. In order to do this type of work safely some suggestions are included herein. THE MAIN HAZARDS ARE AS FOLLOWS:

1. HAZARDS ASSOCIATED WITH THE MAGNETIC FIELD OF 9.4 TESLA:

   1. MAGNETIC TOOLS:
      Ferromagnetic tools (primarily wrenches which are used to tighten the high pressure driving nuts) can be captured by the magnetic field (these magnetic objects can injure personnel if they are caught between the magnet and the object or can cause the magnet to quench - lose vacuum in the dewar - then helium boiloff soars and complete loss of liquid helium coolant results). The solution to this problem is to use non-magnetic tools made of berylium copper, vanadium, titanium, or ampco alloy if possible but these materials are not always available for the tools of interest. Therefore magnetic tools must be used with caution to avoid capture by the magnet. Incidentally stainless steel tools are not necessarily non-magnetic and should be checked beforehand.

   2. PRESSURIZING APPARATUS:
      The high pressure generating apparatus includes ferromagnetic materials as well so it must be secured either to the wall or the floor to avoid capture by the magnet and must be an adequate distance from the magnet so that the magnetic field homogeneity is unaffected.

2. HAZARDS ASSOCIATED WITH HIGH PRESSURE TRANSMITTING FLUIDS:

   1. LIQUIDS:
      Even though most of our our experiments are done with low compressibilty liquids (hence fairly low stored energy) fairly dangerous situations can develop such as ejection of electrical feedthroughs at high velocity.
      If allowed to escape the high pressure liquid also can penetrate the eyes or skin and make wounds which heal only with difficulty - especially with liquids which may be poisonous. One especially should wear eye protection in the form of safety glasses.
      
   2. GASES:
      The use of gases present a more difficult problem since a large amount of stored energy will be involved when the system is pressurized. Some work with gases may be reasonable with our present apparatus. These would include low pressure gases such as carbon dioxide and nitrogen.
   
   

3. HAZARDS ASSOCIATED WITH MATERIALS TOXICITY:

   1. PRESSURISING FLUIDS:
      Liquids: Carbon Disulfide-(CS2) forms a highly toxic vapor and is potentially toxic by absorption through the skin. Becaues of these problems we have dropped the use of this iquid in favor of the more inert electronic cleaning solvent-fluroinert.
   2. Gases:
      Carbon dioxide and nitrogen are fairly innocuous except for asphyxiation problems in high concentration. Nitrous oxide

   3. PROBE MATERIALS: Berylium Copper BeCU: Potentially toxic, basically because of the 1-2 % of beryllium alloyed with the copper.
      1. Toxic by breathing dust, especially during grinding of parts.
      2. potentially by ingestion of the solid particles.
      3. and by absorption through the skin, i.e. wash hands after handling probe parts. Be is known to form wounds that will not heal. Because of this all handling with rubber gloves is recommended. Because of the unique low diamagnetic susceptibilty properties of this material we have found it irreplaceable by anyother known intermetallic alloy for high resolution high pressure NMR.
      Titanium: It may explosively react with oxygen, especially under pressure.

Conclusion regarding safety aspects of high pressure NMR studies

Manual for operation Procedure for the high pressure NMR apparatus:

High Pressure NMR Probe installation:

It is important to follow the instructions below precisely in order to obtain satisfactory results from the high pressure NMR probes. In order to reduce exposure to beryllium and fluorinert these procedures should bedone using vinyl gloves, these seem to be stronger than latex ones.

Remove the normal DMX400 NMR probe in use from the magnet as discussed in the probe section instructions. Put the probe in the ring stand holder with the probe bottom extensions sitting on the ring stand surface. (Do not sit the probeon the capacitor tuning wands as this will ruin the capacitors and require much labor for their replacement).

Remove the pressure screw and upper plug from the top of the probe. Do this by first loosening by use of two(2 open end wrenches (1" non-magnetic and 1.5" magnetic(careful with this one)) by turning opposite from one another. The pressure screw must !!never!! be tightened or loosened by holding the probe body as this will destroy the probe electronics as the pressure cell is not well connected to the probe cover.Prepare the NMR sample in a custom medium wall sample tube from Wilmad of ID 4.2 mm and of length 5.9 mm and flat bottom.

Fill the sample tube using a glass pipette leaving about 1 inch space empty at the top. Next push the pressure transmitting piston with two o-rings into the sample tube while at the time turning the piston. This dual motion protects the o-rings from disintegration.

Push the piston in leaving at least 1/4" open space at the top. At any rate try to remove all the air bubbles. Screw in the piston screw and tighten with a small screwdriver.

Next put the NMR sample in the high pressure probe upside down and while slowly rotating it, push it down flush with the upper c-seal surface. Do not force the sample as this can destroy the proton coil inside the probe.

Add sufficient fluorinert using a glass pipette to cover the NMR sample tube-again flush to the c-seal. Do not put in excess as this liquid is fairly expensive, $100 per bottle. The liquid should not leak out the bottom if the bottom pressure connection was kept properly closed as below.

Now screw down the top pressure plug and tighten as above.

Put the high pressure NMR probe into the magnet. Turn the lever to lock the probe in place.

Connect the one pressure lead and tighten with non-magnetic wrenches. In order to minimize liquid loss and contamination all pressure connections should be tightly covered except during installation. All pressure tubes are kept full of liquid at all times so that there should be no air in the system.