"Serial dilution provides a simple means to measure amounts of a substance smaller than the resolution of available measuring techniques would otherwise allow. Most individuals lack a readily available method of determining mg amounts of a substance, and especially amounts less than 100mg.
To get around this limitation, you can create a solution of a given substance with a known, fixed concentration, and then measure the mass of the compound in solution by measuring a given volume of said solution. In the above example, dissolving 100mg of a compound in a quantity sufficient of solvent to achieve 100mL of solution will result in a wt./vol. concentration of 1mg per 1 mL of solution (which concentration may also be stated as 1/10th of 1%). It is much easier, relatively, for a layperson to accurately measure 1 mL of a liquid solution than for the same individual to weigh out 1 mg of the solid itself. Generally, the most accurate means of achieving this concentration will involve diluting the compound in some volume of diluent (solvent) LESS than the desired final volume. For example, dissolve 100mg of solid in 80 mL of solvent, then, upon complete dissolution, bring the final volume to 100mL. If you dissolve 100mg of solid in 100mL of solvent, your final volume of solution will be greater than 100mL (almost always), and this will make your concentration somewhat less than 1mg/mL. Now, for the caveats.
The above method is dependent on several assumptions. The first, and most obvious, would be the original weight of the solid to be dissolved. If you are relying on the stated weight of a compound, as shipped, and the weight was not accurate to begin with, you'll have no idea what the actual final concentration of your solution is. So, even though you don't have to weigh 1mg of your solid, you still absolutely must accurately determine the initial weight of the quantity to be dissolved. If you cannot do this, the serial dilution method is of no use. You are also bound by the assumption that the purity of the compound, as stated, is within acceptable limits of error. If you purchased 100g of a compound with a stated purity of 99.9%, but the compound as supplied is actually only 90% pure, your final concentration will again be less than desired.
A second consideration is the physical stability of the solution, not only microbiologically (as was alluded to above), but chemically. If the compound you are attempting to dissolve isn't stable in the presence of your diluent, and you proceed with the solution anyway, you've just managed to deactivate your compound (e.g. a compound susceptible to acid hydrolysis would not be a good candidate for an aqueous system, so no water as solvent in that case).
In a similar vein, you have to provide for complete dissolution of your compound in your chosen diluent, or again, your final concentration will be skewed. The result will be a supersaturated solution with a lower than desired concentration, and residual solid compound that presents the same potential complications as the dry compound did to begin with (i.e. issues of toxicity). A bit of research beforehand will provide you the absolute solubility of your compound with respect to commonly available diluent.
Supposing all goes well, and you achieve of solution of known concentration that actually contains the desired amount of the compound you had in mind to begin with. Unless you have access to GC/MS, and the associated relevant standards (test compounds for comparison), you still can't vouchsafe your solution for the presence or absence of chemical impurities. And therein lies a tale. There are several well documented instances of trace impurities in compounds subsequently ingested by humans (or other test mammals) that have resulted in catastrophic, irreversible and sometimes fatal toxicities. The thing is, you won't know for sure for another hour or so. Or maybe tomorrow. Or maybe next year.
Lastly, if your solution is the desired concentration, there are no significant impurities, no bacterial contamination, chemical or bacterial degradation and you manage to accurately measure an appropriate quantity of active component, you STILL have no real data pertaining to the potential acute toxicity of the compound in question, nor the potential long term sequale (physiological consequences) of its use intermittently or chronically. "
J'ai eu la chance de discuté avec lui à propos du dosage volumétrique et de la pureté des RC qu'on peut trouver (Il est très ouvert et ne renie pas les questions quand on parle de drogue).
