Morphologically Directed Raman Spectroscopy (MDRS)
Morphologically Directed Raman Spectroscopy is a powerful high-resolution technique that combines Static Image Analysis and Raman Spectroscopy. A sample analyzed by Static Image Analysis can have a subset of particles within the particle size distribution targeted for Raman Spectroscopy. This can be used to confirm particles are a specific material, separate populations of materials within a formulation based on Raman spectra, and/or identify unknown particles not exhibiting morphological characteristics expected of the sample. The limitations of the technique are the size of the particle, particle interaction with the instrument’s laser, Raman activity of the particle, and signal of the mounting material (liquid medium, filter, etc.).
As an emerging technology, there is no specific guidance for MDRS, but both Image Analysis and Raman Spectroscopy are recognized by numerous standards and guidance agencies, including the ISO, ASTM, USP, and EP. Moreover, the FDA has increased its requests for companies to evaluate MDRS, specifically in the evaluation of subvisible particles. When a sample is suitable, the information can refine data submitted to the FDA to be more specific to a material of interest, ignoring excipient particles.
The high resolution of Image Analysis combined with the identification capabilities of Raman spectroscopy allows for better refinement of shape categorization of particles within Image Analysis distributions or separation of populations of materials that are morphologically similar. MDRS can be a valuable tool in isolating the size distribution of a specific material within a mixture of materials. Common applications include QA/QC batch testing, general survey screening measurements, and comparative studies.
Due to the complex nature studies relating to identification, PTL recommends reaching out to discuss your testing needs to evaluate the suitability of this analysis for your material.
Advantages
- Ability to potentially speciate particle size distribution within a mixture
- Targeted identification of contaminants or outlier particles
Considerations
- Particulate must be ~2 µm or larger in size, and scatter in the Raman spectra
- Not appropriate for metallic substances, or very dark or black materials
- This technique does not offer full chemical composition analysis
- Lower counts than image analysis
Sample Requirements
Ideal sample amount is up to 1 gram for solid samples.
For liquid samples, the preferred amount is 20 mL.
The above sample quantities are preferred. If sample availability is further limited, please contact us to share specifics about your sample and options for suitable sample quantities.
Detection Range
Particulate must be approximately 2 micrometers (µm) up to approximately 1300 µm in size to obtain Raman Spectroscopy results. Appropriate size range is dependent on Raman scatter of a material. The 2 µm minimum size threshold is based on high scattering materials.
Data Reported
A typical Raman Spectroscopy analysis will include the Raman spectra analysis of representative particles, comparison to the known spectra, and discussion about the results.
For MDRS, the particle size distribution analysis will be reported, counting at max 1,000 particles, based on suitability, as well.
Please contact us to learn more about the various reporting options.
Sample Reports
Instrumentation
Particle Technology Labs uses the Malvern Morphologi 4-ID for our image analysis and MDRS testing.
