Buffer help - Another buffer question, with a different approach (Dec/15/2009 )
I see quite a lot of buffer questions, but this one has a bit different approach, I think. Ok, I'm supposed to make a buffer consisting of:
10 mM Na2HPO4, pH 7.2
20 mM NaCl
5 mM EDTA
25% (w/v) sucrose
I will be needing really small amounts of this, I'm thinking around 20 mL and will only use it once if everything goes as planned.
So I was thinking I'd do 100 mL in case I would need some more. This means I'd need:
0.117 g NaH2PO4*H2O
0.163 g Na2HPO4
0.0117 g NaCl
0.146 g EDTA
25 g sucrose
And to me, those amounts seem way to small for me to handle and to get close to anything accurate. But if I'd simply bring it up a factor 10 and dilute it later, I'd need alot of sucrose so I wouldn't want to do that either. If I'd save the sucrose, I wouldn't know how much water to use in the first place. Any tips?
I just realised that sucrose is normal sugar. Then it's really no problem to use 2,5 dL sugar, because it doesn't really cost anything. Dang, just by being in that packaging everything seem so much more expensive.. Well, I'm getting used to it. I'm using alot of IPTG though, because I can't seem to wrap my head around that 2 mL of that stuff is quite costly..
What I like to do is mass out small stuff inside an ependorff on a scale (a sensitive one - to the nearest 0.0001 g), then dissolve it in water and pour it into a falcon tube, then add more water to the eppendorf and repeat until I'm satisfied it's all been transferred.
I guess you could freeze whatever you're not using at -20 until needed.
You can perhaps make stock solutions of the constituents seperately. Then dilute them when making the final buffer. Stock solutions of EDTA especially can be used for loads of other buffers.