In a personal letter, the student wrote me a question.
I am particularly interested in exploring the application of UV-Vis spectroscopy as a method for assessing drug solubility in oils which serves as a crucial initial step in the selection of suitable oils for nanoemulsion formulation. However, I have encountered challenges regarding the immiscibility of oils with methanol that is used as a solvant, as commonly mentioned in literature. I am hopeful that you could provide guidance or insights into the procedure involved in utilizing UV-Vis spectroscopy for this purpose.
My answer:
1. What kind of emulsion? oil/methanol or oil/methanol,water?
2. The drug is distributed between two phases and must be absorbed in the UV-Vis region. Oil should also absorb in the UV area.
3.Oil/methanol heterogeneous system. It remains so after the formation of a nanoemulsion.
My first reaction would be to check if his oil/methanol emulsion may lead to scattering in the wavelength region he wants to use.
If so, this may well prevent any attempts at measuring anything by absorption.
New student question. This is a water-oil emulsion, my task is to choose a suitable oil phase. To achieve this goal, I intend to evaluate the solubility of the drug in various oils. However, I encountered discrepancies in the methodology outlined in several articles. They suggest diluting oils containing the drug with methanol before analysis by UV-visible spectroscopy. However, oils and methanol are known to be immiscible, raising concerns about the feasibility of this approach. Therefore, I need your expertise to determine the most appropriate approach to determine drug solubility using UV-visible spectroscopy.
My answer. If this is an individual hydrocarbon, then it is necessary to construct a calibration graph of absorption intensity - concentration of your drug in this hydrocarbon and determine its concentration. It is not necessary to use methanol. The problem is that your drug may dissolve in water. To do this, you can determine the partition coefficient of the drug between water and hydrocarbon and make an adjustment for its solubility in water.
I add excess drug to the oil, solubilize it,
filter in a 0.22 um filter and extract the liquid twice with an immiscible solvent, separating the oil from the solvent in a funnel, I mix the two extractions and read the absorbance and calculate
Louhana Moreira Rebouças
It is necessary to determine the solubility of the drug in a microemulsion, and not in oil, as you suggest.
Louhana Moreira Rebouças
immiscible solvent - with water, oil? What solvent?
oil solubility test does not contain water test with methanol if your drug is soluble in it....for testing on the nanoemulsion it is different, remove the water from the nanoemulsion by lyophilization and extract the active ingredient with a solvent that solubilizes the drug and is immiscible with the oil
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