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Ruthenium Red - solubility, purity and optical density (molar extinction coeffic - (Sep/11/2013 )

We bought a new batch of Ruthenium Red  from Tocris (Cat.No.: 1439, 100 mg powder). Based on literature RR(=Ruthenium Red) has a molar extinction coefficient around 61000-68000 /M/cm at 533-538 nm. However, this newly bought product gives only about 4500-7000  /M/cm (533 nm) in spite of the sonication/stirring/or warming and stirring (60 C, waterbath) of the stock solution (3mM, 5mM and 10 mM, in distilled water). So we have also problems with solubility, but this huge difference at mol.ext. coefficient can not be explained by the less serious problem on solubility. The biological effect of this new RR is also much less than that of the previous stock (rather old from another firm). 
Thank you very much for your kind help in advance!
Gabriella Braun
PhD student


the apparently lower extinction coefficient may be due to impurities. have you taken % purity into account?