# Probe dilution for FISH - (Jul/11/2011 )

Hello,

I need to dilute fluorescent probes for FISH.I need a final concentration of 200ng/ml Probe nmol = 13.8 Probe MW = 17672.00

As what I know is to how to make a 100 uM stock solution by adding 138 ul of TE or water .

Could anyone help me in this.

Thanks in advance.

200ng/ml is 200mg/l (I've changed to litres because it's easier to compare to molar concentrations that way)

17672g of probe would be 1 mole so:

0.2g (200mg) of probe would be 0.2/17672 moles = 1.13173 x 10^-5 moles

so you want your probe concentration to be 1.13173 x 10^-5 M (as this^ is the number of moles you need in 1 litre)

1.13173 x 10^-5 M = __11.3173uM__

If you are making the 100uM stock solution, then you would dilute this further to get the above concentration.

If you are wanting to make this concentration instead of the 100uM solution, you would dilute the the pellet in 1.219ml. (see below)

You have: 13.8 nmol and need to find volume to dilute.

You want: 1.13173 x 10^-5 moles per 1 litre.

13.8 nmol = 1.38 x 10^-8 moles

1.38 x 10^-8 divided by 1.13173 x 10^-5 = 0.001219368 (this is therefore the fraction of 1 litre you need)

0.001219368 x 1 litre = 0.001219368 litres

0.001219368 litres = __1.219... ml__

_______

You don't need to use as many steps as that, but I tried to explain where the numbers came from... Hopefully I didn't confuse things further as I have a habit of explaining maths badly....

Also, there are many ways of working these kinds of things out, so someone else may suggest a different method that suits you more.

Sorry, there is a mistake right at the start of this.

200ng/ml is 200**ug**/l, __not__ 200**mg**/l

This alters everything by a factor of 1000.

How embarrassing.