[freeze0912]

I got 2 questions of the IR analysis
Thanks for answering me the below questions:

1. If there is moisture presents in the sample of KBr, what is the effect of the IR spectrum?
I found in some books that the moisture will exhibit the peak in 3450 - 1640 cm-1, but how do the moisture effect and the degree of the effect?

2. Why KBr and sample need to be grinded when performing the KBr pellets prepartion for IR analysis?
My tutor said that KBr acts as the solid solvent, but what is the effect if I don't add it and just perform the IR analysis with sample only.
And I found that KBris used for making the glasslike transparent disk and absorb the moisture, does there any other reasons?

Thanks again to all of us that think and answer my stupid questions

[marquis]

1.  You learn to recognize moisture peaks in the IR very quickly.  The peaks are present in the range you mentioned.  But, unlike normal peaks, moisture peaks are very broad. 

You can look up the spectrum of water in most IR books.  If you can't find the spectrum, put a very small amount of water on salt plates (NaCl, not KBr) and run an IR.  Most professors do not like this approach, because the water will dissolve the salt plates.  So only use a very small amount of water. 

2. You need some method for putting the sample in the IR beam.  You will find a number of those, including plastic support films, nujol mull on salt plates (KBr or NaCl), etc.  The usual problem-there is way too much sample (sometimes you will be told the sample is too thick).  This gives a very poor (and very hard to interpret ) IR spectrum. The answer, in your case, is to dilute the sample with KBr and then run the sample.

Hope this helps... 

[freeze0912]

For the answer1, I will try when have chance to use the FTIR again

For answer2, can I say KBr is the solid solvent in this method?

[Train]

Regarding grinding the sample during preparation: in addition to serving to mix the sample with whatever medium (eg KBr or Nujol) you're using, it also serves to ensure a small particle size so that scattering of the IR beam is minimized.

I don't think solvent is the right term for the KBr (or Nujol) because what you're creating is more like a mixture or suspension than a solution.