science(chem)

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What would cause the peaks in a IR analysis to be smaller than they should be? My sample had the right peaks where they should be and they were the right shape but were shorter then they should be.

Something different is what the y axis says on the IR analysis that they gave us so we would know how the IR was supposed to look for our samples. But the y axis on the one they gave us said "percent transmittance" while the IR graph had "percent reflectance". Not sure if it's the same.

If they are though then an example of the difference in peak size is:

my sample of 4-bromo-2-chloroacetaniilide
1 middle sized peak: 3275.24 cm-1
and the intensity was : 69.608 % reflectance

The given IR card showed the peak going all the way down to about 30% percent transmitance ( I don't have the exact value)

Thank you.

  • science(chem) -

    Something different is what the y axis says on the IR analysis that they gave us so we would know how the IR was supposed to look for our samples. But the y axis on the one they gave us said "percent transmittance" while the IR graph Ihad "percent reflectance". Not sure if it's the same.

  • science(chem) -

    The only explanation I might offer is that you may have performed an ATR (attenuated total reflectance) but I haven't had experience with that instrument. .

  • science(chem) -

    Oh..yes I did perform an ATR. I didn't think it was that different from a normal IR but I guess it is from what your saying.

  • science(chem) -

    Thank you Dr.Bob

  • science(chem) -

    I don't know that it's different. I've not used one.

  • science(chem) -

    Well, you don't need solvent and you just use the sample as is.

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