Analysis of Particle Identification by SEM-EDS (CAT#: STEM-B-0368-CJ)

An SEM is essentially a high magnification microscope, which uses a focussed scanned electron beam to produce images of the sample, both top-down and, with the necessary sample preparation, cross-sections. The primary electron beam interacts with the sample in a number of key ways:-
1. Primary electrons generate low energy secondary electrons, which tend to emphasise the topographic nature of the specimen.
2. Primary electrons can be backscattered which produces images with a high degree of atomic number (Z) contrast.
3. Ionized atoms can relax by electron shell-to-shell transitions, which lead to either X-ray emission or Auger electron ejection. The X-rays emitted are characteristic of the elements in the top few μm of the sample and are measured by the EDX detector.

Biopharmaceutica

1. Cleaning, fixing, drying, attaching to a platform and coating with metal or carbon has to be performed before imaging.
2. Sample preparation.
3. Ionisation of the sample: ejection of electrons from the atoms within the sample (whereby they are converted into excited ions), producing the secondary electrons.
4. Reflection (back-scattering) of the beam electrons from the sample surface, producing the backscattered electrons.
5. relaxation of the excited ions formed in process 3 accompanied by emission of X-rays.
6. EDS detects and identifies the X-rays (as in the XRF method) that are emitted in the course of the above mentioned process by the excited ions formed upon electron bombardment on the surface of the sample.

• Sample: Particle-based APIs (e.g., VLPs, liposomes, polymeric nanoparticles), Virus Particle, Protein Formulations
• Equipment: SEM-EDS

• Advantage: Can provide chemical identity of particles and complex particles, can be automated to provide particle distributions, images and morphology, no interference with water can perform in solution phase.
• Disadvantage: Fluorescence can interfere with signals. Small volume for analysis (~70 µL).
• Sample Size Range: 0.1 nm – cm.