Trouble taking Raman spectra in solution.

[Pills07]

Hello everyone!
I´m new to the forum and to start participating and being part of it I have the following problem and question:

I began using a dispersive Raman system and I got spectra of Rhodamine B and heparin sodium (and anticoagulant and glycosaminoglycan) in solid form and the spectra are good,but when I take the following:
1.Rhodamine B dissolved in ethanol and deionized water.
2.Heparin dissolved in deionized water and benzyl alcohol.

I get the solvents spectra,which to me is kinda weird because at least water is supposed to be a weak Raman scatterer.To prove that I got the wrong spectra to say it somehow I took spectra of the solvents alone and what I tried to do was subtracting the spectra (as done in UV-Vis spectroscopy) still I couldn´t see any of the peaks typical for heparin nor Rhodamine.
The system used is a Renishaw InVia Raman microscope,the spectra are taken at standard and ambient conditions,we have three lasers 457 nm,515 nm and 785 nm,I used the last one.I put the samples on an eppendorf cover (in an upside down position so the liquid sample can be poured in it) because we have no sample holders nor cells available for now.
So what am I doing wrong?,is it the way the I prepare the sample,would I have to do anything regarding the laser handling? what do you think?

 

[Pills07]

I correct,sorry:
actually they are 4 solutions,if someone reads it as I have it in the original post then it can be thought it´s a mixture,so the four solutions I am having trouble with are:
1.Rhodamine B in ethanol.
2.Rhodamine B in deionized water.
3.Heparin in deionized water.
4.Heparin in benzyl alcohol.

 

[Claude Bile]

I will suggest the obvious first; perhaps the solution is too dilute?

Claude.