100.5% Methamphetamine Hydrochloride, How?

[Rasputin]

Hey All: The following is just something that I have been noodleing off and on for about a year now, it might be a stupid question, or maybe not, it might get me flamed, or it might not, in any case I just have to know, its been bothering me for to damn long.

About a year and a half ago someone gave me an old copy of Remington's Pharmaceutical Sciences(Fourteenth Edition), its a pretty neat book, lots of useful imformation and other cool stuff, and I have learned alot, however one part of it puzzles me. When you look up a drug in this book(I will use Meth.HCL as the example, since this is the Stimulants Forum) it gives you all the basic imformation,Preperation,Dose,Solubility,Uses,etc. Now I know what all that stuff means, but at the very top of the drug facts it will say something like, "Methamphetamine Hydrochloride contains 98.5-100.5% of Meth.HCL, calculated on the dried basis", what does this mean?

I thought 100.00% purity was the most you could have of anything, or maybe it doesent mean purity, maybe it means.... ahh fuck, I dont know. What does this mean. Its not just Meth, almost all the drugs say this(sometimes upto 102.00%). Ive asked around, and no one has been able to give me an answer, one guy said it has something to do with recrystalization(but I doubt that)but, the general answer given was "I dont know". So I am going to turn this question over to the most brilliant minds I know of, Hive Bees. I really hope someone can answer my question, its just been bugging the hell out of me for about a year now.

P.S.  If anybody feels like flaming me for asking a stupid question(if this is one), please feel free to do so. Just do be kind and please include the answer(or how to find it)in your flame.

Thank You

[ChemoSabe]

All I can think of is that it could be a comparison of the weight of the freebase form to the HCl form. Just a wild guess.

[cublium]

I've had lots of chemical bottles labeled "assay % 98,5-101,5" for example.I think it means how many percent of net weight compromises pure substance and that way it could also be over 100% since bottle can always contain more than label says.

[ChemoSabe]

I think the topic of percentages is his all time favorite subject.

See this related thread

Post 525008 (missing)

(pink_dust_angel: "what does % mean?", Newbee Forum)

That thread deserved a nomination for "the most stubborn argument of the year" award.

[Chimitant]

Maybe it has to do with the way the purity of said compound is determined. I remember doing quantitative GC analyses. I had to inject solutions with  different concentrations to construct a calibration line (quantity/detector response relation) When using a calibration line it is possible to have a value over 100%, for instance when injecting a sample a second time. The response can be slightly higher, depending on a number of factors that detrmine the outcome of an analysis. Every result of a measurement will have a certain uncertainty which will add to the real value. In this way one can get +100% results. Just a guess...

[Newton]

Chimitant has it right. Every measuring procedure has a certain imprecision, which is also knwon as the 'error bar'.
In the given case, if your equipmnet gives you a reading of '99.5% puritiy', and this device has an imprecision of '+- 1%', yould would quote '98.5%-100.5' as the result of the measurement. The correct value will be in this range.