Raman spectroscopic methods for component particle analysis
The invention relates to methods of assessing one or more geometric properties of a particle of a substance using a Raman spectroscopic property of the substance. The method is useful, for example, for assessing particle sizes and size distributions in mixtures containing both particles of the substance and other materials.
1. A method of assessing a geometric property of a particle of a substance in a sample, the method comprising irradiating the sample, generating a first image of Raman-shifted radiation scattered from the sample at a Raman shift value characteristic of the substance, and determining the geometric property from the image.
2. The method of claim 1 , wherein the image is an image of a microscopic field.
3. The method of claim 1 , comprising simultaneously determining the geometric property of multiple particles of the substance in the sample.
4. The method of claim 1 , wherein the geometric property is characteristic of the size of the particle.
5. The method of claim 1 , comprising generating an image of Raman-shifted radiation scattered from the sample at multiple Raman shift values characteristic of the substance.
6. The method of claim 1 , further comprising comparing the first image and a second image of Raman-shifted radiation scattered from the sample at a Raman shift value characteristic of a compound other than the substance.
7. The method of claim 6 , wherein the first and second images are combined in an aligned manner.
8. The method of claim 6 , comprising determining the geometric properties of the particle of the substance and of a particle of the compound in the sample.
9. The method of claim 1 , further comprising comparing the first image and a second image of the sample generated by a spectroscopic method other than Raman spectroscopy.
10. The method of claim 9 , wherein the first and second images are combined in an aligned manner.
11. The method of claim 1 , wherein the image is a two-dimensional image.
12. The method of claim 11 , wherein the geometric property is selected from the group consisting of the area, the perimeter, a Feret diameter, the maximum chord length, a shape factor, and an aspect ratio of the particle.
13. The method of claim 1 , wherein the image is a three-dimensional image.
14. The method of claim 13 , wherein the geometric property is selected from the group consisting of the volume, the surface area, a Feret diameter, the maximum chord length, a shape factor, and an aspect ratio of the particle.
15. The method of claim 1 , wherein the particle is irradiated with substantially monochromatic light.
16. The method of claim 15 , wherein the light has a wavelength in the range from 220 to 1100 nanometers.
17. The method of claim 15 , wherein the light has a wavelength in the range from 280 to 695 nanometers.
18. The method of claim 15 , wherein the light has a wavelength of about 532 nanometers.
19. The method of claim 1 , wherein the particle is irradiated with laser light.
20. The method of claim 1 , wherein the particle is immobilized prior to generating the image.
21. The method of claim 20 , wherein the particle is immobilized by depositing the particle on a surface.
22. The method of claim 20 , wherein the particle is immobilized by freezing a liquid in which the particle is suspended.
23. The method of claim 20 , wherein the particle is immobilized by suspending the particle in a polymer resin and curing the resin.
24. The method of claim 1 , wherein the particle is obtained from a composition in which particles that comprise the substance are mixed with particles that do not comprise the substance.
25. The method of claim 24 , wherein the substance is a pharmaceutically active agent.
26. The method of claim 25 , wherein the agent is mixed with an excipient.
27. The method of claim 25 , wherein the agent is formulated for aerosol delivery.
28. The method of claim 25 , wherein the agent is formulated for parenteral delivery.
29. The method of claim 25 , wherein the agent is formulated for oral delivery.
30. The method of claim 25 , wherein the agent is formulated for topical delivery.
31. The method of claim 1 , wherein the particle is a solid.
32. The method of claim 1 , wherein the particle is a first liquid dispersed in a second liquid.
33. The method of claim 32 , wherein the particle is selected from the group consisting of an oily liquid droplet in an oil-in-water emulsion and an aqueous liquid droplet in a water-in-oil emulsion.
34. The method of claim 1 , wherein the particle is a micelle.
35. A method of assessing a geometric property of a particle of a substance in a sample including multiple particles, the method comprising irradiating the sample, identifying the particle of the substance by assessing Raman-shifted radiation at a Raman shift value characteristic of the substance, generating an optical image of particles in the field, and determining the geometric property of the particle of the substance from the optical image.
36. A method of assessing particles of a first substance and a second substance in a sample, the method comprising irradiating the sample, generating a first image of Raman-shifted radiation scattered from the sample at a Raman shift value characteristic of the first substance, and comparing the first image with a second image of Raman-shifted radiation scattered from the sample at a Raman shift value characteristic of the second substance.