It’s unlikely that there would be a simple separation, unfortunately.
The pKa of metatomidine is 7.2 and the pKa of fentanyl is 8.4. The pKa is the pH where 50% of the molecules are ionized, and 50% aren’t.
At acidic pHs below the pKa (for amine/basic molecules) the molecules will be charged and soluble in polar solvents. Above the pKa and the molecules will be uncharged and soluble in non-polar solvents.
With tight control of pH you can separate compounds that differ in pKa, but for liquid-liquid extractions, which approach the limits of home chemistry, you need at least a difference of 3 pKa units to achieve a safe degree of purification as the closer they are, the more of a mixture it is. Laboratory techniques such as chromatography or counter current extraction could possibly separate these compounds, but these methods require specialized equipment.