0
$\begingroup$

I have an aqueous solution of methylene blue. How do I determine the concentration of this solution, so I can duplicate it?

$\endgroup$
2
  • 3
    $\begingroup$ Do you have access to a UV-VIS spectrometer? $\endgroup$ Feb 13 '15 at 20:04
  • $\begingroup$ As @KlausWarzecha said, what kind of equipment/instruments do you have access to? $\endgroup$
    – wes3449
    Feb 13 '15 at 20:38
3
$\begingroup$

The concentration of an aqueous solution of methylene blue can be determined using a UV-VIS spectrometer.

Measure the absorption at $\lambda = 664\, \mathrm{nm}$, use the molar extiction coefficient of $95000\, \mathrm{dm^{3}\cdot mol^{-1}\cdot cm^{-1}}$ (Reference) and calculate the concentration using the Lambert-Beer equation.

$\endgroup$
2
$\begingroup$

If in addition to a UV-VIS spectrometer you also have access to a fluorimeter, I would recommend using fluorescence instead of absorbance. It will be more sensitive and less prone to interference. However, fluorimeters are more expensive and harder to come by than UV-VIS spectrometers which measure absorbance only.

When I measured methylene blue by fluorescence, I used 630 nm for excitation and 700 nm for emission. I found fluorescence to be much better than absorbance at 670 nm for the same samples, but the absorbance measurement also worked. The fluorescence properties of methylene blue are less well-known than the absorbance. Other papers often use different values for excitation/emission than what I used, but if you have a fluorimeter you can determine what's best for you.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.