Dilutions questions

Nov 2013
I have an issue where I think I'm just confusing myself with a simple question. Here are the directions I'm following :
"Apply 200 ul of 1 nM Fluorescein(375g/mol) in 0.01 M NaOH solution to wells."

Assuming total volume is 1L - 10mL NaOH with 990mL H20 should give .01M NaOH
I can't figure out the 2nd part. Thinking of it logically, 1M fluorescein would be achieved by adding 375g of it, so I assume .000000375g / L would be 1nM.

This doesnt seem to make any sense since it's not practical to weight out that small amount so it can't be what the instructions are asking.
Any help on this is greatly appreciated. Thanks!


CHF Hall of Fame
May 2010
You can achieve such small concentrations/amounts per litre by serial dilution.

Let's take an example. If you have 0.01 M of NaOH and put 10 mL in 990 mL, you'd end up with 1 L of 0.0001 M NaOH.

Repeating with 10 mL of 0.001 M of NaOH, you get 0.000001 M NaOH.

And if you use 1 mL of NaOH and 999 mL of water each time, you get the dilution even faster!

1 mL 0.01 M NaOH + 999 mL H2O => 1 L 0.00001 M NaOH