Hi,
We run Infra red for a Sample with reference to the Reference Standard of the sample.
Then we found % matching between sample and standard.
The results indicates the sample is matching at 40% to the standard.
Is there any limit for the matching % in IR?
Example: Not less than 80%, Not less than 90%, Not less than 90% etc?
Whether IR can be used for quantitative measurement or its only qualitative.
In my experience FTIR is used for a qualitative match. We compare the sample with the reference standard. They are usually prepared the same day using the same procedure. The comparison uses the actual peak maxima. You should have the same major peak maxima. The peak size and shape should be similar, but not necessarily identical due to minor differences in sample preparation.
Sometimes you may be using FTIR to identify an unknown. When looking at an unknown versus a library the match percentage is your only approach. Generally, a match at 90% or greater is a comfirmation. The difficulty arises if you sample is not a pure substance.
Dear Stephan,
Thanks for your reply. The IR profile matches to only 40% but the same material complies to Assay by HPLC method 99% and this method is validated.
Can we say the material complies?
This material is not official in monograph also
I would not use % match. Compare peak maxima. Your software should give you this for the sample and standard (separately ).
Mr. Ponnuraj ,
Yes this is quantitative analysis of macrocomponents, but at a significantly low level of reliability, applicable mostly for monocomponent mixture an dpractically unaplicable to mixtures with components more than 5 (even 2 depending on the complexity of the IR pattern)
So you used the same method for both the standard and the unknown? You may need to do some chemometrics (PLS, etc) to make a good calibration for your sample. It would be a lot of up-front work, but in the long run it would work as a quick screening process for quality control. I definitely agree that you need 90%+ for a positive match in IR and that more than a small number of constituents will be very difficult to do.
So if this is the case even if the material complies to Assay by HPLC method (More than 95%) we cannot say the material complies since it did not match IR with standard (Less than 60%)?
You may need to isolate the active ingredient from the matrix with solvent, evaporate the solvent , then run the ftir to get a better match. With you present approach, this is not considered to be a positive ID.
This discussion actually needs spectra to continue. Remember that vibrational spectroscopy can detect differences in Form (polymorphic, salt, hydrate, solvate) that are not possible with chromatographic methods. Both your hplc and IR data are probably correct - you need to understand your sample to make sense of the data set you have.
Don has the correct response. Relying on percentage figures for identification is potentially dangerous. Looking at the spectra will show if you have a good match. With thin films water vapour and CO2 inbalance can affect the score. With a halide disc, unless you weigh it out, a large amount of impurity in the sample such as salt can still respond with a high percentage match.
Don and Geoffrey are right: first, show the spectra. Then, try to subtract the IR spectra of the vapour(s), CO2, solvents, matrix, pollutants, etc. before you try to subject your sectra to any software that tries to make a decision. Unlike UV-VIS, IR deals with narrow lines - even in proteins the FWHM is about 10 cm-1, and you should be able to use your eyes to separate the spectral region where "unwanted" contributions are minimized - let's say COOH, Amide, finger-print, HOOP, methyl and methylene, etc., and then focus on this region.
Good luck,
Andrei
You cannot compare the %match of IR analysis with HPLC result. HPLC analysis gives you the % assay, i.e. the actual content of the sample against a reference standard. The % match you get in IR analysis is only the spectral match against a std spectrum. There are many factors which can cause some deviations in both the sample and standard spectra. So you have to go by HPLC analysis result for assay. Coming to second part of your question: Yes, IR can be used for quantitative analysis. Moderen FTIRs have excellent quantification capabilities.Here, you require a reference standard for making different concentration standard solutions. The most critical part is to identify a certain band in your sample which is clearly separated from others. You can then fix the start and end wavenumber limits for this band . Once this is done, you have to scan all your std preparations and sample solution within this range. The s/w will then create a calibration curve and from the calibration curve the sample concentration will be automatically calculated by the s/w.
Hi, Mahmood can you share the details of Pharmacopoeia which is stating this?
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