# dilutions again!please check - molar dilution (Nov/29/2008 )

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[quote name='Alejandro' date='Dec 3 2008, 08:26 PM' post='159396']
Dear Alejandro
Thanks very much indeed you cleared up many thinks in my mind. Really appreciated.

Kindest regards,

-DElizabeth-

QUOTE (merlav @ Dec 4 2008, 12:35 PM)
For any solution preparation go to: http://www.graphpad.com/quickcalcs/Molarityform.cfm

Cheers, I have this website. I really needed someone to double check what I am doing and read a lot since then about calculations. I can say calculations are really no problem for me now:)

Best wishes

-DElizabeth-

[quote name='Alejandro' date='Dec 4 2008, 01:26 PM' post='159499']
Hi, itÂ´s a wonderful page, but it might be better to leave it for double checking.
I jus think that learning how to prepare solutions is part of the basic training. And asking someone to check on your calculations actually leads to learning new ways to do stuff. Examples? Did you know that it is a LOT easier to dissolve high concentrations of BSA (Albumin) by putting your solution in the fridge? You can go to 20% in minutes ( and I learned by asking someone to check my calculations because I could not dissolve).

A.

Preperation of PMA (above) given by you was a good example. I didnt know that so very usefull for me to ask.

-DElizabeth-

QUOTE (Gat @ Nov 30 2008, 03:03 AM)
Hi Elizabeth,

The first part of your calculation is correct - you need 0.61683mg powder in 1ml in order to achieve a final C of 0.001M.
As for the rest of the calculation - I didn't completely understand... what I would do, is simply weigh 0.61683mg, and add 1ml of fluid. True - this method considers the powder V as negligable.

Good Luck...

QUOTE (DElizabeth @ Nov 30 2008, 12:22 AM)
Hi there, I am new to calculations and need help! I am trying to make PAF (PHORBOL 12-MYRISTATE 13-ACETATE) solution whose MW is 616.8. PAF is supplies as 1mg powder. How can I make 0.001M solution? Is the following calculation correct?

616830mg(616.8gr)=1M in 1000ml
0.61683 =0.001M in 1ml

1:0.61683= 1.62 so I add 1.62 ml to 1mg of PAF. Then this final conc. is 0.001M in 1ml.

If I take out 50microlitres of final conc. does it become 5x10^-5M. As I saw someone elses calculation like this 5microlitres of 10^-3M stock +495microlitres would make 10^-5 M. So this final 10^-5 is in 500microlitres isnt it?

Please expalin this to me thoroughly as it is ruining my lab life!!

cheers,

First of all you should NEVER try and weigh 1mg or less....it's almost impossible to do. If the company supplies 1mg of chemical then BELIEVE THEIR QC/QA...it's more than their "jobs worth" to get it wrong.

The first cheat I ever learnt in the lab was the following:

MW =100

Then 1mg in 10 mls = 1mM ( 1000uM)

MW=600

Then 6mg in 10mls = 1mM ( 1000uM)

and so on and so on.

Most compounds I have ever used in drug discovery are less than 1mM

Therefore your compound has a MW of 616.8

6.168 mg in 10mls = 1mM

Therefore 0.6168 mg in 1ml = 1mM

Therefore 1mg in 1.62ml = 1mM

easy really

Kindest regards

Rhombus

p.s It is always good to have a table of the different ways of expressing concentrations:

0.001M = 1mM = 1000uM =10-3M

Always have fun in the lab

Rhombus

-Rhombus-

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