0.2 M Sodium Acetate Buffer - (Aug/27/2019 )

I have a bit of confusion. I need to make 0.2M NaOAc buffer (as per the papers I am following). Now there are 2 different recipes of "sodium acetate buffer" available and that has got me confused. One is straight forward, following CSHL protocols

Now that is perfectly fine for me (except that I need pH 3.5-4.0 so all I need to do is to add a bit of extra acetic acid)

But here's another recipe

"Acetate buffer pH 3.6–5.6 Stock solutions A: 0.2 M solution of acetic acid (11.55 mL in 1 L distilled water) B: 0.2 M solution of sodium acetate (16.4 g of C2H2Na or 27.2 g of C2H3O2Na.3H2O in 1 L distilled water) x mL of A plus y mL of B, dilute to a total of 100 mL with distilled water."

Ref: https://link.springer.com/content/pdf/bbm%3A978-1-59745-425-4%2F1.pdf

(have found the same recipe in one of the old book on buffers available in print in our lab)

Apparently, people in my lab who have worked previously on similar experiments have used this later recipe while calling it 0.2M NaOAc buffer. In my opinion this (later) recipe cannot make a 0.2M buffer solution, it's something else. Papers other than our own group have usually used the specific term "0.2M NaOAc buffer (pH xyz)". Wondering what these other people are calling as NaOAc buffer?

Can someone explain what am I missing here?

The people in your lab are wrong - if you take a 0.2 mol/l solution and then dilute it with water, you always end up with a less concentrated solution.

The paper you linked has this to say, right above the acetate buffers section:

 

The accuracy of the following tables is within ±0.05 pH at 23°C. The molarity of the buffer described is between 0.05 M and 0.1 M

  Note the bolded part...

If you want an easy buffer calculator try here: https://www.cusabio.com/m-296.html#a01

bob1 on Tue Aug 27 12:20:40 2019 said:

The people in your lab are wrong - if you take a 0.2 mol/l solution and then dilute it with water, you always end up with a less concentrated solution 

 

 

I agree with you, the final concentration of NaOAc in this case is 0.07M.

My worry is actually a bit more than just the 0.2M NaOAc buffer. I am trying to do enzyme mimicking experiment with a few nanoparticles and the NaOAc buffer I make based on the CSHL protocol always turns the TMB/H2O2 solution blue without nanoparticles. This is clear cut indication of contamination.

When I use the other recipe (0.07M one), it doesn't show any color in the absence of nanoparticles (haven't yet tested with the nanoparticles though so it may actually be that due to low molarity of the buffer the reaction isn't happening at all).

Ah - in that case, while they are incorrect about the concentration, they are correct about the use!

It's been a while, but I think last time I used TMB in an acetate system, that the concentration of the acetate was around 0.1 mol/l, though I see that the original paper used 0.2 mol/l. If the system is working in the lab as-is, I wouldn't change it, even if they are mistaken in their nomenclature (other than to get them to change how they refer to the buffer perhaps). This is the sort of information that gets lost when you move on to another lab and someone tries to repeat your experiments, only to find that because you were using proper 0.2 mol/l and they used 0.07 mol/l that the results are different!