Well. You may use the cyclic voltammetry and check the peak potential and its intensity.

Do I understand correctly that you are working in aqueous solutions?

Thank you for the kind replies dear sirs, @VolodymyrTkach and @YuriiVGeletii.

Yes, sir, my planning is to work on aqueous electrolytes for the conversion of NaBO2 to NaBH4.

might be helpfull

http://fsl.npre.illinois.edu/Project%20Presentation/fuel%20cell%20project_files/July%20workshop%20presentations/uiuc-talk-25July2005.pdf

thanks for the kind reply dear sir, @YuriiVGeletii

IR. Peaks around 2300-2400 cm-1 can't be confused with much else. not the best technique for aqueous solution though, you;d have to isolate and dry. Raman better for aqueous solution, A1 totally symmetric BH4 str breathing mode at 2310 cm-1. such peaks provide positive fully diagnostic evidence. Also note: if attempting to make Borohydrides in aqueous solutions, ensure your pH is well higher than 7, otherwise you risk evolving significant boranes and hydrogen, possible explosion or fire. (nice green flames though, see my profile pic!)

Thank you Dear sir @Francis Mair for the kind reply