Magnetic purification of a sample

1. A method for separating magnetic nanoparticles comprising: providing a sample comprising a plurality of magnetic nanoparticles; passing the sample through a first magnetic field; at least partially isolating magnetic nanoparticles of a first nanoparticle size desired; altering the strength of the first magnetic field to produce a second magnetic field; and at least partially isolating magnetic nanoparticles of a second nanoparticle size desired.

2. The method of claim 1 , further comprising synthesizing a plurality of magnetic nanoparticles.

3. The method of claim 1 wherein the magnetic nanoparticles comprise iron oxide nanoparticles.

4. The method of claim 1 wherein the sample comprises a plurality of polydisperse magnetic nanoparticles.

5. The method of claim 1 wherein the first magnetic field and second magnetic field are supplied by a magnetic separator.

6. A method of isolating magnetic nanoparticles of a desired size comprising: providing a sample comprising a plurality of magnetic nanoparticles; passing the sample through a first magnetic field to remove at least a portion of the magnetic nanoparticles in the sample having an average diameter substantially less than the desired size; altering the strength of the first magnetic field to produce a second magnetic field of sufficient strength to isolate at least a portion of the magnetic nanoparticles of an average diameter substantially greater than the desired size; and recovering the magnetic nanoparticles of the desired size from the magnetic field.

7. The method of claim 6 , further comprising synthesizing a plurality of magnetic nanoparticles.

8. The method of claim 6 wherein the magnetic nanoparticles comprise iron oxide nanoparticles.

9. The method of claim 6 wherein the sample comprises a plurality of polydisperse magnetic nanoparticles.

10. The method of claim 6 wherein the first magnetic field and second magnetic field are supplied by a magnetic separator.

11. The method of claim 6 wherein the step of recovering at least a portion of the magnetic nanoparticles of the desired size from the magnetic field comprises passing a solvent through the magnetic field.

12. A method for separating magnetic nanoparticles from non-magnetic substances comprising: providing a sample comprising a plurality of magnetic nanoparticles; and passing the sample through a low magnetic field gradient that is less than about 100 Tesla per meter.

13. The method of claim 12 wherein the magnetic nanoparticles comprise iron oxide nanoparticles.

14. The method of claim 12 wherein the low magnetic field is supplied by a magnetic separator.

15. The method of claim 12 wherein the sample comprises a plurality of polydisperse magnetic nanoparticles.

16. A method of removing arsenic from a sample comprising: providing a sample comprising arsenic; introducing into the sample magnetic nanoparticles; allowing the magnetic nanoparticles to interact with at least a portion of the arsenic; and passing the sample through a magnetic field to remove at least a portion of the arsenic.

17. The method of claim 16 wherein the step of passing the sample though a magnetic field to remove at least a portion of the arsenic comprises using a magnetic separator.

18. The method of claim 16 , further comprising passing the sample through a magnetic field to remove at least a portion of the magnetic nanoparticles.

19. The method of claim 16 wherein the magnetic nanoparticles comprise iron oxide nanoparticles.

20. The method of claim 16 wherein the magnetic nanoparticles comprises a plurality of polydisperse magnetic nanoparticles.