1:1 Dilution an Oxymoron? - (Oct/10/2007 )
Please help me clear up a misunderstanding between coworkers. Sorry for the long post. Here goes:
Is saying "make a 1:1 dilution" an oxymoron? I realize when people say this they probably mean mix 1 part "X" with 1 part diluent, but shouldn't this actually be called a "1:2" dilution? A 1:10 dilution doesn't mean mix 1 part "X" with 10 parts diluent; it means mix 1 part "X" with 9 parts diluent to make 10 parts total, correct? So following the same logic, a 1:2 dilution means mix 1 part "X" with 1 part diluent to make 2 parts total, right? A 1:1 dilution would then mean mix 1 part "X" with 0 parts diluent to make 1 part total - not a dilution at all!
The reason I ask is that a coworker asked me to prepare a 1:2 dilution of a stock, so I mixed 1 ml of the stock with 1 ml diluent (PBS) to make 2 mls total. She claims she meant mix 1 part of the stock with 2 parts diluent to make 3 mls whole. I argue this is actually a 1:3 dilution, so that's what she should have asked me to do. She says I am wrong, that I actually made a 1:1 dilution, and that her way is a "true" 1:2 dilution.
Who's right? Seems less important the more something is diluted (i.e., for a 1:1000 dilution, 1ul + 999ul may as well be 1ul + 1000ul), but at the low end it really makes a difference.
Sorry if this seems obvious to some but I have been trying unsuccessfully to clear this up. "1:1 dilution" dilution seems commonly used, but what's the difference between this and a "1:2 dilution"?
I think it is very ambiguous to say 1:x. Much better is to say simpy "dilute it 20-times, or 3-times". Then it is completely obvious. I think for most people:
1:1 means 2x dil.
1:2 means 3x dil.
1:10 means 10x dil.
I guess in case of 1:3 50% of people would say 3x and the rest would say 4x.
Your co-worker will learn to specify it as 3x dilution.
I guess I am one of those stranger people. And perhaps I am wrong but to me
1:1 means undiluted stock
1:2 means half concentration.
1:3 means 1/3 concentration
1:10 mean 1/10 concentration
And why should 1:1 dilution be an oxymoron? How ever will you specify an undiluted solution? 1:0? which to me means infinite concentration.
perneseblue: At least your way of thinking is consistent, which is not a disadvantage in research 
But what would you say, if somebody told you: "diute your stock 1:1 in PBS"? I guess that person means 1 part stock and 1 part PBS, not 1 part stock and 0 part PBS. Why else would he say PBS, if he could as well say "molten led", which sounds much cooler anyway 
yeah, much cooler.
I guess my reaction would be 
Fatal Error.
I would have to ask for clearer instructions. 
As you have mentioned, it is probably better to write things long hand.
hmmm...
1:1 means one to another one (1+1)
1:10 means one to another ten (1+10)
1/1 means one in one total (1+0)
1/10 means one in ten total (1+9)
so lac1278 you are wrong i'm afraid
its the difference between a ratio and a fraction (come on people this is GCSE stuff)
btw 1/10 in this case refers to one in ten not one tenth (same thing really but it'll just confuse)
dom
Hi,
I agree with Kupac on the intepretation of 1:1 to 1:10 ratio (NOTE: don't prefer to call it "dilution") but I think there's an error in 1:10, shouldn't that be a 11X dilution since the final volume is 11 "parts"?
Cheers
P.s. Totally agreed with Dominic.
There's no error there. What I meant was that I think there is a fine transition between the two "systems". I.e. 1:10 is 10X, while 1:2 is 3x, and I have the feeling that the transition happens somewhere around 1:3 or 1:4. Those are the ratios where 50% of the people would do according to the "small number" system, and the other 50% according to the "large number" system. Just imagine: 1:100 means 100x, nobody would do 101x
Anyway, it is not about what you think, because I'm sure that everybody has his/her totally consistent system. But it is about how people interpret 1:2 in general. And that is not consistent. Therefore it is totally wrong to use the "x:y" style in protocols. The meaning of X-times dilution or x/y is clear for everybody, so those are preferred. And if somebody uses the x:y system, then he/she should not be surprised if another person gets it wrong. So I guess lac did the right thing (in his system ofcoz).
?? How is it that people don't remember (or never learned in elementary school) what the colon( means?
http://en.wikipedia.org/wiki/Ratio
It's standard mathematical notation. 2:3 means 2 parts + 3 parts. 2:3:1 means 2 parts + 3 parts + 1 part.
Even if many people get this wrong it's no reason to do away with the notation. People should ask a 3rd grader and learn what it means. It's like saying we shouldn't use Normality because too many people don't understand it? Or we shouldn't use English because too many people don't understand it.
That said - I always get confused with the ratios, lets never dilute anything ever again!