dilution dilemma - lost with calculations (Sep/13/2010 )

I am constantly finding myself lost when doing serial dilutions and calculations...can someone plz shed some light on these problems:

10 microliters added to 1000 microliters----what is the dilution factor? is it 10/1000 = 0.01?

100 microliters added to 900 micorliters is a dilution 1:10, the dilution factor is 0.1?

50 microliters added to 1000 microliters----Dilution factor is 50/1000 = 0.05?

250 microliters in 9ml----Df = ?

Finally is 1:10 the same dilution as 1/10 in calculations???

Thx so much in advance for any help

Hola, all your developments are corrects. 250 ul in 9 ml is 250/9000, 900/25= 36 so your dilution is 1/36.Another way, 250/9000= 25/900 = 5/ 180 = 1/36 Good luck

maryjo on Mon Sep 13 19:17:19 2010 said:

Hiya, just being picky here but need to point something out. Your calculations are fine as long as you are talking about final volumes. Reading it the way you say it will be slightly different, minor differences but might be important.

10ul added to 1000ul, would actually be a 10/1010 dilution, ie: 1/101 or a 0.0099 dilution factor.
The same for 50ul added to 1000ul, would be 50/1050 or 5/105 a 0.0476 dilution factor.
As for 250ul in 9ml, it will end up being 250/9250=5/185=1/37 or a dilution factor of 0.027.

These examples result in small differences, but is very important with dilutions to take the final volume in account as it can change your concentrations. A 1/10 dilution is addition of 1ul to 9ul.

Sorry if I sound a bit pedantic, I've learnt from my own mistakes in the past

oh, and yes 1/10=1:10

i m a bit confused here..
adding 50 microliters to say 950 microliters i.e final volume being 1 ml, wont the dilution factor be 1000/50 = 20 and not 50/1000 = 0.05???!!!!!

wat i mean is wen u get a result from the diluted sample, u generally multiply with the dilution factor to get the final value and which in this case will be 20 and not 0.05!!!
correct me if i understood this wrong!!

thankx!!!

Prep! on Tue Sep 14 09:02:38 2010 said:

Prep, you are totally right, but we are not completely wrong either

Apparently we are getting DILUTION factors with CONCENTRATION factors mixed up, see here: http://biology.clc.uc.edu/fankhauser/Labs/Microbiology/Dilutions.htm

Final volume/Aliquot volume = dilution factor
Aliquot volume/Final volume = concentration factor

So, in your example to get the final value you will either multiply by 20 or divide by 0.05, which is the same.

I've never really thought about it in terms of dilution or concentration factors, but if is 50ul in a final 1000ul, si a 1:20 dilution = 1/20 which si 0.05.

Hopefully I've not ended up confusing people more.


reason for editing: wrongly posted before finishing writing the post

haha
okiee dokiee!!!
atleast my mind is at the right place!!!

Great...thx for all the help! Im glad to see that im not the only one that finds these things confusing

maryjo on Tue Sep 14 16:42:10 2010 said:

why wud anyone be glad cause others are confused too!!!

Hahaha its a releif to know that the defect isnt in my brain, but in the numbers