Hi Mithra,

I think you can use either Isopropyl alcohol (2-propanol) or absolute ethanol. 

If they are quartz-cuvette means, Frist  clean with Potassium permanganate  then cleans with any alcohol or acetone solvent or any solvent   

The idea is to remove adsorbed impurity at the glass surface or they could be released in the solution later (even if the cuvette is sealed). A long time ago, I was using sulfochromic (during 24 hours) but it is now forbidden (in France). I think people uses strong bases or strong acids to clean glass cuvettes (for example piranha solutions). Have a look on google with piranha+solution. Then rinse them with filtered water and filtered ethanol or acetone and dry them under a hood (laminar flux) with a clean gas. Finally nothing easy but very effective ;). With that technique, a cuvette filled with pure filtered water stays clean (dust free) for at least several weeks.

Regards

The best cleaning methods starts with identifying the best solvent for the impurities you want to remove. Notoriously difficult to clean are cuvettes that contained proteins. Flushing with warm SDS solution can be helpful. Very strong and corrosive solvents ultimately dissolve the glue used (if any). I used a setup that sprayed distilled acetone in the cuvette that was turned upside down as ultimate cleaing step. Using acetone from a bottle often introduces residues of material that dissolves in acetone.

In the end one realizes that cleaning is basically flushing with enormous amounts of very pure solvents. My favorite sequence (for biophysical studies) was warm SDS -> MilliQ water -> methanol -> toluene -> methanol -> MilliQ water. The sulfochromic method mentioned by Jean-Cristophe worked very well but is forbidden now (in the Netherlands). Take the normal lab precautions when using warm SDS, methanol and toluene!

There are a several ways to clean cuvettes, and the most convenient (if your samples allow this) may be to just use disposable polystyrene... For quartz cuvettes there is a commercial solution [Hellmanex] just make sure you rinse with copious amounts of water. For many samples, a simple series of NaOH + acetic acid + H2O rinses may be enough. The best way to test the cleanliness of your cuvette is to measure the scattering intensity of your solvent, ensuring that your solvent is clean to begin with (might have to filter through low pore size like a 20nm Anotop filter).

http://www.materials-talks.com/blog/2015/09/15/how-to-clean-a-quartz-flow-cell/