CH2Cl2 is strong organic solvent may this colour from contaminated bottle.
you can wash the bottle using chromic acid ( 1 L H2SO4 + 5 g KCrO4) and if your bottle contaminated with any organic compound the washing solution changing from pale yellow to pale green)
Thank you so much for your answers. Finally, It was not a problem of degradation, but the molecule was being mixed with the previous molecule that I mesured before, benzoquinone which is very sticky.