Dilution help - (May/22/2016 )

Hello,

I need help determining dilution factor. I add 2uL of substance X into 58uL of Buffer A (total 60uL) for a 1/30 dilution of substance X.

I then add 60uL of Buffer B into the mix for total of 120uL volume now. I take 50ul of this and read it twice on a quantification machine for ng/ul. The readings are 12ng/ul and 13ng/ul, average 12.5ng/ul.

What is the concentration of substance X? Is it still 12.5ng/ul or is there a dilution factor to multiply it with?

Hello, I have an answer of 1/60 as the final dilution of the substance X.

Should I multiply 12.5ng/ul by 60 = 750ng/ul ?

When doing calculations you should look at the steps you took and work from those. Treat it like a word problem you did for maths at school.

Your sample when measured had a concentration of 12.5 ng/ul

This was diluted 1:2 in buffer B, so 12.5 x 2 =25 ng/ul, however...

you also diluted in buffer A 1:30 therefore 25 x 30 = 750.  So multiplying by 60 was correct, but if you show your working, then it is easier to see why and will lead to fewer mistakes.

Hello
Yes thanks. I calculated it out as you wrote it to obtain the 1/60 answer I got. But I got stuck in the end if it was 1/60 or was it a 1/2 dilution and it is why I posted, to confirm my answer. Thank you.

SUbstance X concentration = k
First dilution = 1/30
Second dilution = 1/2
Total dilution = 1/30*(1/2) which is 1/60 (as you described)
concentration of 1/60 of substance x is on average 12.5 ng/ul
what is the concentration of substance x?

If converted to equation:
1/60*k = 12.5 ng
determine k value.

Hope this helps.