RogueRose
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What is the standard test for quantitative analysis of compounds?
I've watched videos on GCMS, LCMS, HPLC and some new "raman spectroscopy" technology. It seems that all these tests are great at identifying a
compound, basically it seems by the molecular weight or by it's UV signature (and whatever the raman spectroscopy uses). The thing is that I haven't
seen any of the videos or writeups explain how a sample can be tested for the amount of a compound in a sample.
For example a 500mg APAP pill that is mainly the API but has some binders/fillers. How can it be determined that the pill has the 500mg "as
advertised". Is there one specific test that is best for this and have I missed something in these tests that allows them to do quantitative
analysis?
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DraconicAcid
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Nearly all forms of spectroscopy can be used quantitatively. I'm sure you know how UV-Vis spectroscopy can be used to determine the amount of a
solute, following Beer's Law, right? You can do similar measurements with everything else, particularly if you've run your sample through a column
and separated it from everything else.
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Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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DrP
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Yea, he's right.. most of them can be used quantitatively... you can crudely measure peak heights with a ruler against a known marker in the
compound... or if you know you have an unknown ration of known things you can compare peak heights. I would assume most modern kit has a way you can
integrate under peaks and things and could give you ratios for compositions.
NMR is a powerful technique for quantitative results. For organics I would say NMR is the go to for quantitative analysis of a structure.... again,
it depends on exactly what you are trying to measure. In your example I do not know the chemistry so couldn't say... but comparison of the peak
heights of what you are looking for against the impurities will give you a ratio... you could then take the total mass and split that according to
the ration of the compounds in your mix. Might be hard for an industrial product though.
Raman spec has been about for a while and is Basically IR with opposite selection rules for visibility... so you can do IR spec on things that are
usually not IR visible. iirc it is a surface technique that gets seriously enhanced when you set up a resonance with surface plasmons on little silver
or precious metal islands of the right sizes. You look for the IR absorbed and re-emitted at 90 degrees to the surface... this (very weak signal)
gives the Raman spec.
\"It\'s a man\'s obligation to stick his boneration in a women\'s separation; this sort of penetration will increase the population of the younger
generation\" - Eric Cartman
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Texium
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Thread Moved
27-11-2023 at 12:12 |
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