Vijai:

Before I can provide you with more information, I would like to know more about the biomass samples that you are trying get the Raman spectra of. Also, what are their chemical compositions - extractives and lignin amounts in particular. How colored are they, on a scale of 1 to 10, with 10 being cotton (or bleached chemical pulp) and 1 being unbleached wood pulp.

Umesh

Further to the response of Unesh - if your sample doesn't absorb at 785nm, it doesn't fluoresce. Your backgrpound could be due to scattering, in which case see this for suggestions on ways to reduce the background

"In vitro analysis of immersed human tissues by Raman microspectroscopy",

F. Bonnier, A.Mehmood, P. Knief, A. Meade, W. Hornebeck, H. Lambkin, K. Flynn, V. McDonagh, C. Healy,T.C. Lee, F.M. Lyng, H.J. Byrne,

Journal of Raman Spectroscopy, 42, 888–896(2011)

Thanks all.

Umesh, they are crushed feed stock of cotton plants.

Wesley, i checked the sample but no burning observed.I used 10x with 10% 785nm laser.

Huge, i will check and get back if i have problems.

This is what I think is happening.

Cotton straw (CS) has about 60 % carbohydrates, 18% lignin, 9% protein, 7% other organic matter, and 3% extractives. The fluorescence is likely to come from every thing except carbohydrates and that is the fraction you want for Raman, to be able to calculate crystallinity. We have reported crystallinity (by 380-Raman) of a lots of lignocelluloses but CS is not one of them. Corn stalk is the one that comes close. See the link  below for more details.  Your best bet would to 1) extract the sample and then 2) delignify the sample by methods outlined in this paper. If you still see fluorescence interference then try NaBH4 treatment (also in the same paper). I have not used 785 nm Raman for Raman but have used 1064 nm Raman and these treatments usually work for such samples. Let me know what happened.

Umesh

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