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Topic: Please help me with this methylene blue calculation.  (Read 7001 times)

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Offline dingleberry

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Please help me with this methylene blue calculation.
« on: January 26, 2011, 11:53:19 AM »
Okay. I have a 1% liquid methylene blue. I assume this means 10 mg of methylene blue per ml. Please correct me if I'm wrong.

Okay. Lets say I take 1 ml of this and mix it with 100 ml of water. This will give me ~100mcg of methylene blue per ml, yes?

So, starting with a 1% methylene blue solution, how many ml of water do I need to mix one ml with to get 60mcg of methylene blue per ml?

Thanks.

Offline DevaDevil

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Re: Please help me with this methylene blue calculation.
« Reply #1 on: January 26, 2011, 12:24:39 PM »
Okay. I have a 1% liquid methylene blue. I assume this means 10 mg of methylene blue per ml. Please correct me if I'm wrong.

a % is always mass/mass, or volume/volume (in case of water your assumption is almost correct as water has a density of close to 1 g/ml)
so 1% solution means either 1ml of methylene blue per 100ml water, or 1 mg methylene blue per 100mg water, depending on if it is mass% or vol%

Offline Vidya

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Re: Please help me with this methylene blue calculation.
« Reply #2 on: January 26, 2011, 12:26:42 PM »
your first two steps are perfectly right
now you can work for the last part in the same manner

Offline dingleberry

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Re: Please help me with this methylene blue calculation.
« Reply #3 on: January 26, 2011, 12:59:20 PM »
I'm 39, and exhausted.  Please help.

Offline DevaDevil

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Re: Please help me with this methylene blue calculation.
« Reply #4 on: January 26, 2011, 01:17:02 PM »
1 ml of your solution added to 100 ml of water will have a concentration of 10mg / 0.101 l is about 100 mg / l, or 100 microg. / l.

in formula:
you start with 10 mg = 10000 microg.
you need to add Vw volume of water to reach 60 microg per milliliter;
Cend = 60 microg/ml = 10000 / Vtotal
Vtotal = Vw + 1 ml (starting volume of your methylene blue)

so:
60 microg/ml = 10000 / Vtotal ==> Vt = 10000/60 = 167 ml
and
Vw = Vt - 1 = 166 ml.


Offline dingleberry

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Re: Please help me with this methylene blue calculation.
« Reply #5 on: January 26, 2011, 01:57:16 PM »
God bless you, DevaDevil.

Offline JGK

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Re: Please help me with this methylene blue calculation.
« Reply #6 on: January 26, 2011, 02:07:53 PM »
A % is always mass/mass, or volume/volume

Have to disagree there, % units can be w/w, v/v or w/v.

In Analytical chemisty the latter two ar more common than %w/w
Experience is something you don't get until just after you need it.

Offline DevaDevil

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Re: Please help me with this methylene blue calculation.
« Reply #7 on: January 26, 2011, 02:23:09 PM »
so what is the convention for %w/v (essentially a mass concentration)
[g/m3]?

I have not encountered it in my field I have to admit, and the dimensionlessness of a % would not be observed in w/v, so it must be well-defined.

Offline rabolisk

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Re: Please help me with this methylene blue calculation.
« Reply #8 on: January 26, 2011, 04:44:43 PM »
Typically it's g/mL. Mathematically, this is flawed since % have to be dimensionless, and since it is possible for a solution to be >100% concentrated. Nevertheless, I have also seen w/v used rather often.

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