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The following message was posted to: PharmPK
I am curious as to the viewpoint of the bioanalytical people on this
discussion group on this topic.
If drug is soluble in organic solvent or aqueous how much % of the
drug should be used for spiking in biological matrix for preparation
of the validation samples?
The use of internal standard (IS) to avoid the variation in the
extraction of the analyte from biological matrix.
What is your opinion on the following aspects of IS-
If we will prepare the internal standard final dilution in water
rather than organic solvent then addition of IS to the biological
matrix before extraction of the analyte from the matrix.
Is the IS will extracted in the same manner as of analyte?
Especially in case of plasma I fill it is good to prepare IS in
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Less than 2.5% of organic solvent should generally be used for
spiking the analyte/IS in matrix. Even while using water, you may not
want to dilute the matrix too much.
The extent of extraction of IS/analyte depends on the extraction
method and not the spiking solvent you are using.
It is always better and advisable to use the same solvent for both
analyte and IS (considering that they are structurally similar).
However if you still want to use a different solvent for spiking IS,
be sure of volume you are adding and consistency of extraction.
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