Introduction
The UV-Vis spectrophotometer is the workhorse of the pharmaceutical development and quality control laboratories and is used to qualify and quantify chromophore absorbing materials in solution.
Functionality
UV Vis spectroscopy consists of passing electromagnetic energy through a sample. Depending on the amount of the substance of interest in the sample, the UV or visible energy will be partially absorbed by the substance in a defined spectra range, the remaining light will reach a suitable detector. The detector then produces the sample's unique absorbance spectra for the defined wavelength range.
The measured absorbance value within a predefined wavelength range will then be compared to a known concentration calibration curve made with traceable standards, and presence and quantification of the substance of interest will then be possible.
The functionality described above requires that the sample must be free of any undissolved portion of the substance of interest, as undissolved particles will make some of the incoming light scatter and not reach the detector.
Practical Challenges when doing Kinetic Solubility/Dissolution/Precipitation experiments:
Kinetic experiments are dynamic assays that aim to understand or investigate the different stages of active ingredients behavior during their change to different matter states, the following picture illustrates the effect of undissolved particles in a sample being dissolved, some of the light will not reach the detector, this is effect is defined as scattering and will show as absorbance contribution in a sample spectrum.
The most common way to reduce scattering from a sample is to filter it, that is, to remove the undissolved particles of the sample. This works fine for end point analysis, however when running kinetic experiments filtering brings along a list of analytical and practical challenges:
- Sample must be removed from the kinetic process, if filtration is not done exactly at the time of sample collection, the kinetic dissolution process might continue until correct filtration stops it
- Some of the undissolved material will be dissolved by the dynamic act of filtration
- Undissolved material entrapped in the filtering material and solution are removed from the experiment, both volume and material loss should be corrected for the subsequent samples to be accurate
- The sample and filtering actions consume time and high numbers of sampling collection are challenging to be taken
The Rainbow R6 Dynamic Dissolution Monitor from Pion Inc. is a unique instrument that allows users to eliminate all the above challenges. In short, it will allow fiber optic probes to read up to 8 kinetic experiments simultaneously inside the environment where the experiment is taking place.
Rainbow R6 along with an 8-channel mini bath with individual stirring speed control, offers the capability to perform solubility, dissolution, precipitation, supersaturation, excipient and formulation rank order screening study experiments. Equipped with optional accessories, Rainbow R6 will also allow you to run flux/permeability studies and Intrinsic Dissolution experiments in a simpler setup than the compendial method described in USP.
Rainbow R6 is equipped baseline correction possibilities included in the data handling of traditional UV-Vis Detector plus2nd Derivative analysis.
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