Methods and systems for low to ultra-low magnetic field nuclear magnetic resonance for detecting chemical nerve agents
A nuclear magnetic resonance (NMR) system is configured to detect chemical threat material. The system comprises a magnet configured to generate a magnetic field of about 300 millitesla or less; and a probe configured to detect nuclear relaxation of at least two nuclei selected from the group consisting of 1 H, 19 F, 31 P and 14 N, and detect the spin density of nuclei selected from the group consisting of 1 H, 19 F, 31 P and 14 N, following excitation.
1. A nuclear magnetic resonance (NMR) system configured to detect chemical threat material, comprising:
a magnet configured to generate a magnetic field of about 300 millitesla or less; and
a probe configured to:
detect nuclear relaxation of a first nuclei that is selected from a group consisting of 1 H, 19 F, and 31 P, and further detect nuclear relaxation of a second nuclei that is selected from a group consisting of 1 H, 19 F, and 31 P, wherein the first selected nuclei is different from the second selected nuclei,
detect the spin density of nuclei from the group including 1 H, 19 F, and 31 P, following excitation.
2. The NMR system of claim 1 , wherein:
the probe defines a hollow space capable of receiving a sample; and
the probe comprises an electrical shield configured to reduce electrical field inside the hollow space.
3. The NMR system of claim 2 , wherein the probe further comprises a detection coil for detecting the nuclear relaxations.
4. The NMR system of claim 3 , wherein the electrical shield is configured to reduce an electrical field generated by the detection coil.
5. The NMR system of claim 2 , wherein the probe comprises:
a first coil configured to detect relaxation of the first nuclei; and
a second coil configure to detect relaxation of a nucleus selected from the group.
6. The NMR system of claim 5 , wherein the at least two nuclei are H-1 and F-19.
7. The NMR system of claim 5 , wherein the first coil does not require retuning between the detections of the at least two nuclei.
8. The NMR system of claim 1 wherein the chemical threat materials are selected from the group consisting of nerve agents, pesticides, insecticides, and organophosphorus compounds.
9. The NMR system of claim 1 , wherein the magnetic field is about 100 millitesla or less.
10. The NMR system of claim 1 , further comprising:
a sample receiver configured to receive a container having a width of about 5.4 cm or less.
11. The NMR system of claim 1 wherein the magnet includes a shim to increase magnetic field homogeneity.
12. The NMR system of claim 1 wherein a J-coupling of a heteronuclear bond such as P—F bond is detectable as a multiplet signal split.
13. The NMR system of claim 11 wherein the multiplet signature identifies the chemical threat material as G-Agent.
14. The NMR system of claim 1 , wherein the magnet is a permanent magnet.
15. The NMR system of claim 1 , wherein the magnet is an electromagnet or a superconducting magnet.
16. The NMR system of claim 15 , wherein the NMR system has a volume less than four cubic feet.
17. The NMR system of claim 15 , wherein the NMR system has a weight less than 150 lbs.
18. The NMR system of claim 1 , wherein the NMR system is portable.
19. The NMR system of claim 1 , wherein the group further includes 14 N, and wherein at least three nuclei is selected, and wherein one of the selected nuclei is 14 N.
20. A method comprising:
selecting a first nuclei from a group consisting of 1 H, 19 F, and 31 P associated with a calibration sample;
selecting a second nuclei from a group consisting of 1 H, 19 F, and 31 P associated with the calibration sample, wherein the first selected nuclei is different from the second selected nuclei;
measuring a first signal amplitude associated with the first selected nuclei from the calibration sample, wherein the measuring the first signal amplitude is performed using a nuclear magnetic resonance (NMR) system;
measuring a second signal amplitude associated with the second selected nuclei from the calibration sample, wherein the measuring the second signal amplitude is performed using the NMR system;
determining a number of atoms for the first nuclei in the calibration sample;
determining a number of atom for the second nuclei in the calibration sample;
determining a first calibration factor based on the first signal amplitude and the number of atoms for the first nuclei in the calibration sample;
determining a second calibration factor based on the second signal amplitude and the number of atom for the second nuclei in the calibration sample; and
deriving a pseudo empirical formula for a molecule based on the first signal amplitude, the second signal amplitude, the first calibration factor, and the second calibrator factor.