suppose i am looking for a Raman peak 1450 per cm in my spectra data obtained from biological sample. However, in spite of applying the same instrumental optimal parameters (e.g. exposure times, power, room temperature ) i obtain Raman peaks e.g. 1446 per cm, 1456 per cm, 1452 per cm and perhaps 1458 per cm. What range / shift is generally acceptable vis a vis what is mentioned in literature? i.e. is it (+5 per cm or -5 per cm), (+10 per cm or 10 per cm) and so on?,...
It would in part depend on the instrument in question. If both use FT-Raman, then your frequencies should be almost exactly the same. (Within 1 cm^-1 or better if the conditions and samples are exactly the same). If one used dispersive Raman (if your detector is CCD, it's most likely dispersive Raman), and internal standard near your peak is not provided, then the deviation can be a few cm^-1. I've found that a dispersive Raman is quite sensitive to temperature of the room throughput the day, probably because it's sensitive to thermal expansion of various elements including the diffraction grating, the detector, and all the optics. FT-Raman doesn't suffer from this problem.
Mr. Githaiga,
This depends on the resolution of your instrument. If the resolution is +/- 0.5 cm-1, then the shifting within X-0.5 to X+0.5 cm-1 is teh acceptable range.
Hello Mr. John
Usually for chemical samples the difference ~2 cm-1 has no matter.
Before each measurenment you have to calibrate the scale of your instrument by recording a standart sample, for example benzene (992 cm-1) or diamand (1332 cm-1). Then you callibrate your instrument or use increment (deviation from standart). Only after this procedure the accuracy of your measurenments can be 1 cm-1.
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