UV-Vis Spectroscopy involves passing electromagnetic energy through a sample. Depending on the concentration of the substance of interest, the UV or visible light will be partially absorbed within a defined spectral range. The remaining light reaches a detector, which produces the sample’s unique absorbance spectrum for the specified wavelength range.
The measured absorbance within the predefined wavelength range is then compared to a calibration curve created using traceable standards. This allows for the identification and quantification of the substance of interest.
For accurate results, the sample must be free of undissolved particles. If undissolved particles are present, they can scatter the incoming light, preventing some of it from reaching the detector.
Practical Challenges in Kinetic Solubility, Dissolution, and Precipitation Experiments:
Kinetic experiments are dynamic assays designed to investigate how active ingredients behave as they change states. The following illustration shows how undissolved particles in a dissolving sample can cause scattering, where some light does not reach the detector. This scattering effect can appear as an absorbance artifact in the spectrum.
The most common way to reduce scattering is to filter the sample, removing undissolved particles. While this works well for endpoint analysis, filtering introduces several analytical and practical challenges in kinetic experiments:
- The sample must be removed from the ongoing kinetic process, and if filtration is not performed precisely at the moment of collection, the dissolution process may continue until proper filtration halts it.
- Some undissolved material may dissolve during the dynamic act of filtration.
- Undissolved material may become trapped in the filter, resulting in both volume and material loss, which must be accounted for in subsequent measurements.
- The time required for sampling and filtering can be significant, making high-frequency sampling difficult.
Rainbow R6: A Unique Solution
The Rainbow R6 is a unique instrument that eliminates these challenges. It allows fiber optic probes to monitor up to 8 kinetic experiments simultaneously, directly within the experiment environment.
Combined with an 8-channel mini bath with individual stirring speed control, the Rainbow R6 supports solubility, dissolution, precipitation, supersaturation, excipient screening, and formulation rank order screening experiments. Optional accessories allow for additional studies, such as flux/permeability and intrinsic dissolution experiments, in a simpler setup than the compendial method described in the USP.
The Rainbow R6 also includes comprehensive baseline correction options, traditional UV-Vis data handling, and 2nd derivative analysis.
