Is there a standard volume that you need to use to reconstitute the residue after extraction of a drug from plasma? Or what should determine the volume of the mobile phase needed to reconstitute the residue?
My thinking is, the larger the volume the lower the concentration of residue and the lower the peak signal.
Initially you should perform a test, then if the concentration is too low we would recommend the method of standard addition.
The other hand, More the volume, you must keep in mind is the concentration. of course, you have a calibration curve, therefore, should worry about getting a good signal.
There's no 'standard volume'. As Daniel Delgado noted, it depends on how much material you have and how much you need in order to get useful data. In our lab, we try to have enough for at least two injections with some left over. If your limit of quantitation, for example, is 100 femtomoles on column, and you think you might have at least 500 femtomoles of analyte, and you want to inject 10 microliters per run, then you might want to reconstitute with, say, 25 microliters. That would give you two injections of at least 200 femtomoles, with 5 micorlilters left over (it's usually not a good idea to use up ALL of your sample). At the beginning of a project, this all has to be worked out experimentally. If you're lucky enough to be working with known compounds, the preliminary work can be done with standards. Also - remember that you should be reconstituting with solvent corresponding to the initial composition of your gradient.
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