Dear Sir. Regarding your issue about how to prepare liquid sample for Raman spectrometer to get good spectrum . Raman spectroscopy is a powerful technique which can have many advantages over other common analytical techniques, depending on the purpose of the analysis. Unlike many analytical techniques which require sample preparation (such as dissolution, grinding, glass formation, or pressing) in order to achieve results, Raman analysis can be made on ‘as received’ samples with no preparation. But  on other  hand you can do preparation for liquid sample. Once a liquid sample has been obtained, either from an original liquid object or from the dissolution of a solid object, the various species of interest must be isolated for analysis. In the case of a liquid suspension, filtration or centrifugation is often performed prior to analysis to remove any solid particles. In the case of a solution, there are many methods available for isolating analytes, including complexation, separation, or extraction. These procedures are performed prior to analysis, for many reasons. Most often, these procedures are performed either to remove any species that may cause interferences in the particular analysis or to provide a means of concentrating the analyte prior to analysis  This is true whether a sample is a solid, liquid, powder, slurry or gas. Place a small drop of the compound on one of the KBr plates. Place the second plate on top and make a quarter turn to obtain a nice even film. Place the plates into the sample holder and run a spectrum. If the sample is too concentrated, separate the plates and wipe one side clean before putting them back together. The KBr plates must be thoroughly cleaned after this procedure to prevent contamination of future samples. Wipe the windows with a tissue, then wash several times with methylene chloride (or another solvent that will take off you sample), then ethanol. Use the polishing kit in the lab to polish the window surface. Wear gloves to prevent fogging. The cleaned surface should be clear and free from scratches. I think the following below links and the attached file may help you in your analysis:

http://www.niu.edu/ANALYTICALLAB/ftir/samplepreparation.shtml

https://application.wiley-vch.de/books/sample/3527321500_c01.pdf

Thanks

Dear Isam, your answer is influenced by FTIR techniques.

Dear Mohammad,

regarding Raman, the signal intensity is heavily influenced by nature of analyte. It would be better to start with an active Raman scatterers like aromatics (say, benzene or toluene). The sample should be preferably placed at the substrate as a thin film (of course, it should be either hermetically closed or placed under fume hood in case of aromatics). The substrate should not give spurious signal; aluminum is usually fine. Sample can be covered by glass or quartz. Excitation laser should be focused at the thin film, preferably, as though it won't excite the cover glass. It is better to use short focal length Raman probe as intensity of Raman-scattered light decreases as R^-2.

Take a look at: https://www.researchgate.net/publication/235410387_Modern_Raman_Spectroscopy_A_Practical_Approach?ev=prf_pub

Book Modern Raman Spectroscopy: A Practical Approach

This question is perfect for being answered by Bruker customer support, isn't it?

Dear Dr. Friedrich, we contacted them and they suggested us something which didn't quiet work. So, i was trying to get others suggestions.

Thanks.

Dear Mohammad, the question is not very clear if you do not precise which kind of liquid - or compound within the liquid - you are trying to analyse.

If you say the transparent liquid gives no results, I think first of an issue of detection due to the optical setup or experimental conditions. Did you check that the laser excitation wavelenght, and power was adapted for the liquid you are trying to analyse? How about the spectral resolution of your optical setup? Did you checked that the pinhole of the spectrophotometer is closed enough to ensure maximum spectral resolution? What is the NA value of the objective you use? Also, what is the container for the liquid? Do you put the liquid on a slide? I suggest 0.1 thin microglass or even better, silica slide which yield lower background.

Then, I would suggest you to use a known liquid such as 100% ethanol, which has a strong Raman signal, to setup and calibrate (x axis) the system.  Then it may be useful to make a "calibration" of the detection limit of the system using solutions of a compound prepared at various concentrations, in fact spontaneous Raman is not good for concentration below mM. This is probably your issue if you expect lower concentrations in your liquid.