NMR使用序言及安全守則
Preface and Safety Guidelines for NMR Usage
NMR Introduction and Safety Guidelines
Welcome to the learning course on NMR instrument usage. First, let's introduce the three basic components of an NMR instrument: the magnet, electronics unit, and computer. The cylindrical part resembles the superconducting magnet of the NMR. This is a 400MHz NMR (approximately 9.4Tesla) superconducting magnet, which was magnetized years ago during installation and remains magnetized unless decommissioned. This means that the magnet part never turns off, regardless of whether experiments are being conducted or not.
The electronics unit, also known as the console, contains RF transmitters, detectors, temperature controllers, signal processors, and so on. As for the computer part, or workstation, it runs NMR operating software (Topspin) to connect and control the operation between the electronics unit and the magnet, as well as to process the experimental data. The RF pulses used in experiments are generated by the electronics unit and then transmitted to the probe inside the magnet via cables at the back of the console.
The probe installed in this instrument is a BBFO (Broadband with Fluorine) Observe Probe. BBFO is a wideband heteronuclear (including fluorine) probe with a positive ambient temperature. It is designed as a wideband two-channel (2 channels) probe, with the outer coil for 1H frequency and the inner coil for 19F to 15 wideband. It is also equipped with a gradient coil, heating device, and fully automatic tuning ATM equipment.
ATM is a small motor used for tuning, as shown in the figure below, installed under the probe, precise and delicate. It operates with the command "atma" or "atmm". Exercise caution when executing this command; if damaged, it can only be repaired by sending it to the original manufacturer in Germany.
This wideband probe can be used for most heteronuclear experiments, two-dimensional experiments, and variable temperature experiments. Since it is an ambient temperature probe, it is suitable for variable temperature experiments, including high and low-temperature experiments. However, training is required for variable temperature experiments. If needed, please contact the administrator.
Below is the ATM hanging under the probe (the square black box with numbers on top).
Next, let's introduce the safety rules in the NMR room, which have two important parts to note: the magnet and the sample tube.
Usually, outside the door of an NMR room, there are various warning signs such as prohibiting entry for people wearing pacemakers, magnetic metal tools, and carts with metal wheels and frames. Items such as credit cards, magnetic cards, student IDs, phones, cameras, keys, watches, and hairpins should also be kept away from the 5 Gauss line of the magnetic field.
The NMR magnet is an extremely strong superconducting magnet. If you have a pacemaker, metal implants, or wear metal jewelry, you may experience the magnet's effects, which can disrupt your heartbeat rhythm or subject you to strong forces, potentially endangering your life. These situations should be avoided.
Additionally, magnetic metal tools are strictly prohibited from being brought into the NMR room. Heavy metal tools attracted by the magnet can cause significant impacts on the magnet, leading to a sudden "quench" of the magnet. This means the magnet enters a catastrophic state. The superconducting coils of the magnet are submerged in cryogenic liquids (liquid nitrogen and helium). Any disturbance to the magnet may result in the boiling of liquid helium, as its boiling point is only 4K. Boiling helium could cause the safety valve at the top of the instrument to open. If you observe a large amount of vapor escaping from the top of the magnet, please remain calm and leave the NMR room promptly.
Please refrain from touching or shaking the NMR magnet as much as possible because it is supported by three air cushions beneath it. Shaking may lead to boiling of the liquid helium.
Although helium gas is non-toxic, a large escape of helium could lead to oxygen deficiency in the air. Inhaling helium may not cause discomfort, but it could result in fainting due to lack of oxygen to the brain. Therefore, it is imperative to leave quickly.
Repairing a quenched magnet can cost anywhere from hundreds of thousands to millions, so besides being cautious, it's crucial to exercise care.
The second part pertains to the sample tube. It's essential to select qualified sample tubes. When inserting the sample, ensure that the pressure from the gas valve is sufficient, which can be felt by the palm of the hand or heard. If you don't feel air pressure above the magnet, check the pressure gauge on the gas storage barrel. It should be at least >5.5kg. If there's no gas pressure, please contact the administrator.
Before inserting the sample tube into the magnet, it needs to be wiped clean, fitted into the rotor, and its depth measured using a depth gauge (for the BBFO, the bottom of the sample tube should be placed at 2.0cm). Ensure that the sample tube is securely positioned in the rotor and not loose or sliding. If it's loose, please replace the sample tube or rotor. Loose or improperly positioned sample tubes can easily break inside the probe of the magnet, which should be avoided.
In the event that the sample tube does break inside the probe, please inform the administrator immediately so that the probe can be cleaned as quickly as possible to prevent contamination or corrosion of the probe coils by chemical substances.
This instrument supports approximately 35 research groups and is used by over 150 students. Let's all take care of and use it responsibly.
