From: Substandard and falsified medicine screening technologies
Characteristic | Infrared | Near Infrared | Raman |
---|---|---|---|
Principle | Fundamental absorptions | Overtone and combination absorptions | Emissions |
Chemical sensitivity | Polar bonds | Polar bonds | Nonpolar bonds |
Inherent selectivity | High | Low (modeling often required) | High |
Sampling mode | Diamond ATR | Diffuse reflectance | 180o backscattering |
Sampling configuration | Intimate contact with sample required | Stand-off detection possible but can be challenging | Stand-off |
Excitation source | Broadband IR | Broadband IR | Monochromatic NIR i.e., 785 and 1064 nm |
Interferences | Water and any packaging | Water, particle size/packing variability and opaque packaging | Fluorescence and opaque packaging |
Minimum sample size required | At least 1 mg | ~ 20–50 mg | ~ 1 mg |
Approximate penetration depths for solid dosage forms | ~ 1–5 μm | ~ 1–5 mm | ~ 10–15 μm |