Cary 630 FT-IR Library matching algorithm

Question

I have recently ran two standards on the Cary 630 FT-IR using the ATR module - qualitative search. One is Heptanes and the other is N-Heptane. 
 I then ran four samples - three were N-Heptane, the other was Heptanes and compared them to the two standards in my library. 
 
 The results: 
 The Heptanes sample gave a 95% match to the N-Heptane standard and only an 88% match to the Heptanes standard. The spectra's look different - extra peak at 700wn/ Intensity of peaks etc. The solvents are not the same - this result would have passed specifications however it should have failed! 
 
 Does anyone use the library matching algorithm as part of routine analysis and have any information on how to avoid false positives/ false negatives ? 
 Is the search algorithm reliable / capable? 
 Is ATR module appropriate for the analysis of liquids?

soccerdad · Accepted Answer

Hi LauraT 
 ATR should work for liquids. You will get less absorbance than if you were running transmission and if you have a very volatile liquid then there is the chance that the liquid will evaporate before the measurement is completed. I think Agilent sells an attachment for their ATRs to help reduce that issue. 
 re. the library search. Someone from Agilent should know better than I here but you may be able to select search ranges in the library search that would help reduce errors. Also depending on which ATR crystal you are using, the default lower value for the search range could be higher than the peak you are seeing around 700 cm-1 
 Kevin

Cary 630 FT-IR Library matching algorithm

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