SPECTROSCOPY SYSTEMS:
Confocal Raman Spectrometer
Principle:
Raman spectroscopy is based on the inelastic scattering of monochromatic light (laser) by molecules.
- When a laser interacts with a sample, most light undergoes elastic (Rayleigh) scattering with no energy change.
- A small fraction undergoes inelastic (Raman) scattering, where energy is gained or lost due to molecular vibrations.
- The energy shift between incident and scattered light provides a molecular fingerprint.
- This helps identify chemical bonds, functional groups, and structural information.
Key Components:
- Laser source: Provides monochromatic excitation (e.g., 488 nm, 532 nm, 633 nm, 785 nm)
- Confocal microscope: Enables high spatial resolution and depth profiling
- Spectrometer: Disperses scattered light into Raman spectra
- Detector: CCD/PMT for signal detection
- Motorized stage: For precise sample positioning and mapping
Key Features:
- Confocal capability: Depth-resolved (3D) analysis
- Non-destructive technique
- Minimal sample preparation required
- High chemical specificity (molecular fingerprinting)
- 2D and 3D Raman mapping
- Multi-mode analysis: Raman, photoluminescence, and reflection measurements
- High spatial resolution imaging
Specifications:
-
Spectral Range (Raman shift):
Typically 50 – 4000 cm⁻¹ (standard range)
Extended capability up to ~6000–10000 cm⁻¹ (depending on laser and configuration) -
Laser Options:
Multiple excitation wavelengths available:
405 nm, 488 nm, 532 nm, 633 nm, 785 nm
1 to 5 lasers can be integrated (model dependent) -
Spectral Resolution:
Typical: 0.5 – 2 cm⁻¹
High-resolution mode (Echelle grating): up to ~0.25 cm⁻¹
Lower-end systems: up to ~4 cm⁻¹ -
Gratings:
Interchangeable gratings:
600, 1200, 1800, 2400 lines/mm
Optional Echelle grating for ultra-high resolution -
Detector:
Thermoelectrically cooled CCD detector (standard)
Optional: PMT / photosensor modules for high-speed -
Spectrometer:
High-throughput spectrometer
Optical range: ~190 – 1100 nm or 400 – 1100 nm -
Focal Length:
Typically, 200 – 750 mm (depends on configuration) -
Spatial Resolution (Confocal):
Lateral (XY): ~0.3 – 1 µm
Axial (Z): ~0.7 – 2 µm -
Scanning / Mapping:
2D and 3D Raman mapping capability
Minimum step size: ~100 nm
Typical scan range (microscopy): ~200 × 200 µm (or higher with stage movement) -
Repeatability:
Approximately ±0.006 to ±0.03 nm -
Additional Modes (in advanced systems):
Photoluminescence (PL)
Rayleigh imaging
CARS (Coherent Anti-Stokes Raman Scattering)
Applications:
-
Chemical Identification :
Identifies API and excipients in pharmaceutical products using Raman spectra. -
Drug–Excipient Interaction Studies:
Detects interactions between drug and excipients in tablets or formulations. -
Raman Chemical Imaging:
Creates 2D or 3D chemical maps showing the distribution of different components in a sample. -
Polymorph Identification:
Distinguishes different polymorphic forms of APIs, which is important for drug stability and bioavailability. -
Particle Analysis:
Determines particle composition and distribution in powders or mixtures. -
Quality Control in Pharmaceuticals
Used to verify uniformity of tablets, capsules, and injectables. -
Non-destructive Analysis:
Analyzes samples without damaging them. -
Surface and Microstructure Analysis:
Studies coatings, layers, and microstructures in materials
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