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De MPA is geen probleem, het mycofenolzuur komt me al de oren uit. Het probleem is echter de 'variable recovery', en dan eigenlijk vooral de recovery. Ik kan je ook nog de volgende zin geven, maar een voorgaande context is er niet. Volgende zin luidt:
"Furthermore, variable recovery of MPA as a function of the presence of co-administered drugs is substantially reduced or eliminated because competition for binding sites on endogenous non-specific binding substances between MPA and other drugs that bind to such substances is reduced or eliminated".
Misschien maakt het stukje na de 'because' iets duidelijk?
Variable recovery is frequently the result of an extraction step which is only partially effective. Sometimes a small adjustment to the procedure solves the problem. First, determine if the problem is due to variable retention or isolate loss during wash steps.
1. Check to see if a larger elution volume will elute more isolate from the cartridge.
2. >Try a stronger elution solvent or various buffer/solvent combinations to find one that consistently elutes all of the isolate. Again, secondary interactions may be a problem (see inadequate elution).
3. Make sure the isolate does not degrade under the extraction conditions.
4. The matrix may contain various levels of compounds which interfere with the extraction. If salts in the sample cause inconsistent retention, dilute the sample with water. A high level of lipids in the sample can reduce the retention capacity of the sorbent for the isolate. This may require the use of a larger sorbent bed.
5. Adjust the sample pH to suppress ionisation of the isolate. Neutral compounds retain better on non-polar sorbents than ionised compounds.
6. In biological samples, the isolate may be protein-bound. Break this interaction by adjusting the pH, adding denaturing compounds, or precipitating the protein.
7. Ensure that the cartridge is being properly conditioned and that flow rates during sample application and elution steps are not too high.